Passing through the earth's atmosphere, light rays change their straight direction. Due to the increase in atmospheric density, the refraction of light rays increases as they approach the Earth's surface. As a result, the observer sees the celestial bodies as if raised above the horizon by an angle called astronomical refraction.
Refraction is one of the main sources of both systematic and random observation errors. In 1906 Newcomb wrote that there is no branch of practical astronomy that has been written about so much as refraction, and which would be in such an unsatisfactory state. Until the mid-20th century, astronomers reduced their observations using refraction tables compiled in the 19th century. The main drawback of all old theories was an inaccurate understanding of the structure of the earth's atmosphere.
Let us take the surface of the Earth AB as a sphere of radius OA=R, and imagine the Earth’s atmosphere in the form of layers concentric with it aw, a 1 in 1, and 2 in 2...with densities increasing as the layers approach the earth's surface (Fig. 2.7). Then a ray SA from some very distant body, refracted in the atmosphere, will arrive at point A in the direction S¢A, deviating from its initial position SA or from the direction S²A parallel to it by a certain angle S¢AS²= r, called astronomical refraction. All elements of the curved ray SA and its final apparent direction AS¢ will lie in the same vertical plane ZAOS. Consequently, astronomical refraction only increases the true direction to the luminary in the vertical plane passing through it.
The angular elevation of a star above the horizon in astronomy is called the height of the star. Angle S¢AH = h¢ will be the apparent height of the star, and the angle S²AH = h = h¢ - r is its true height. Corner z is the true zenith distance of the luminary, and z¢ is its visible value.
The amount of refraction depends on many factors and can change in every place on Earth, even within a day. For average conditions, an approximate refraction formula was obtained:
Dh=-0.9666ctg h¢. (2.1)
The coefficient 0.9666 corresponds to the density of the atmosphere at a temperature of +10°C and a pressure of 760 mm Hg. If the characteristics of the atmosphere are different, then the correction for refraction, calculated according to formula (2.1), must be corrected by corrections for temperature and pressure.
Fig. 2.7. Astronomical refraction
To take into account astronomical refraction in zenithal methods of astronomical determinations, temperature and air pressure are measured during observation of the zenith distances of luminaries. In precise methods of astronomical determinations, the zenith distances of luminaries are measured in the range from 10° to 60°. The upper limit is due to instrumental errors, the lower limit is due to errors in the refraction tables.
The zenith distance of the luminary, corrected by the refraction correction, is calculated by the formula:
Average (normal at a temperature of +10°C and a pressure of 760 mm Hg) refraction, calculated by z¢;
A coefficient that takes into account air temperature, calculated from the temperature value;
B– coefficient taking into account air pressure.
Many scientists studied the theory of refraction. Initially, the initial assumption was that the density of various layers of the atmosphere decreases with increasing height of these layers in an arithmetic progression (Bouguer). But this assumption was soon recognized as unsatisfactory in all respects, since it led to too small a value of refraction and to a too rapid decrease in temperature with height above the Earth's surface.
Newton hypothesized that the density of the atmosphere decreases with height according to the law of geometric progression. And this hypothesis turned out to be unsatisfactory. According to this hypothesis, it turned out that the temperature in all layers of the atmosphere should remain constant and equal to the temperature on the surface of the Earth.
The most ingenious was Laplace's hypothesis, intermediate between the two above. The refraction tables that were published annually in the French astronomical calendar were based on this Laplace hypothesis.
The Earth's atmosphere with its instability (turbulence, refractive variations) places a limit on the accuracy of astronomical observations from Earth.
When choosing a site for installing large astronomical instruments, the astroclimate of the area is first comprehensively studied, which is understood as a set of factors that distort the shape of the wave front of radiation from celestial objects passing through the atmosphere. If the wave front reaches the device undistorted, then the device in this case can operate with maximum efficiency (with a resolution approaching the theoretical one).
As it turned out, the quality of the telescopic image is reduced mainly due to interference introduced by the ground layer of the atmosphere. The earth, due to its own thermal radiation at night, cools significantly and cools the adjacent layer of air. A change in air temperature by 1°C changes its refractive index by 10 -6. On isolated mountain peaks, the thickness of the ground layer of air with a significant temperature difference (gradient) can reach several tens of meters. In valleys and flat areas at night, this layer is much thicker and can be hundreds of meters. This explains the choice of sites for astronomical observatories on the spurs of ridges and on isolated peaks, from where denser cold air can flow into the valleys. The height of the telescope tower is chosen such that the instrument is located above the main region of temperature inhomogeneities.
An important factor in astroclimate is the wind in the surface layer of the atmosphere. By mixing layers of cold and warm air, it causes the appearance of density inhomogeneities in the air column above the device. Inhomogeneities whose dimensions are smaller than the diameter of the telescope lead to defocusing of the image. Larger density fluctuations (several meters or larger) do not cause sharp distortions of the wave front and lead mainly to displacement rather than defocusing of the image.
In the upper layers of the atmosphere (at the tropopause), fluctuations in the density and refractive index of air are also observed. But disturbances in the tropopause do not noticeably affect the quality of images produced by optical instruments, since temperature gradients there are much smaller than in the surface layer. These layers do not cause trembling, but the twinkling of stars.
In astroclimatic studies, a connection is established between the number of clear days recorded by the weather service and the number of nights suitable for astronomical observations. The most advantageous areas, according to astroclimatic analysis of the territory of the former USSR, are some mountainous regions of the Central Asian states.
Terrestrial refraction
Rays from ground objects, if they travel a long enough path in the atmosphere, also experience refraction. The trajectory of rays is bent under the influence of refraction, and we see them in the wrong places or in the wrong direction where they actually are. Under certain conditions, as a result of terrestrial refraction, mirages appear - false images of distant objects.
The angle of terrestrial refraction a is the angle between the direction to the apparent and actual position of the observed object (Fig. 2.8). The value of the angle a depends on the distance to the observed object and on the vertical temperature gradient in the surface layer of the atmosphere, in which the propagation of rays from ground objects occurs.
Fig.2.8. Manifestation of terrestrial refraction during sighting:
a) – from bottom to top, b) – from top to bottom, a – angle of terrestrial refraction
The geodetic (geometric) visibility range is associated with terrestrial refraction (Fig. 2.9). Let us assume that the observer is at point A at a certain height hH above the earth's surface and observes the horizon in the direction of point B. The NAN plane is a horizontal plane passing through point A perpendicular to the radius of the globe, called the plane of the mathematical horizon. If rays of light propagated rectilinearly in the atmosphere, then the farthest point on Earth that an observer from point A could see would be point B. The distance to this point (tangent AB to the globe) is the geodetic (or geometric) visibility range D 0 . A circular line on the earth's surface explosive is the geodetic (or geometric) horizon of the observer. The value of D 0 is determined only by geometric parameters: the radius of the Earth R and the height h H of the observer and is equal to D o ≈ √ 2Rh H = 3.57√ h H, which follows from Fig. 2.9.
Fig.2.9. Terrestrial refraction: mathematical (NN) and geodetic (BB) horizons, geodetic visibility range (AB=D 0)
If an observer observes an object located at a height h above the Earth's surface, then the geodetic range will be the distance AC = 3.57(√ h H + √ h pr). These statements would be true if light traveled in a straight line through the atmosphere. But that's not true. With a normal distribution of temperature and air density in the ground layer, the curved line depicting the trajectory of the light beam faces the Earth with its concave side. Therefore, the farthest point that an observer from A will see will not be B, but B¢. The geodetic visibility range AB¢, taking into account refraction, will be on average 6-7% greater and instead of the coefficient of 3.57 in the formulas there will be a coefficient of 3.82. Geodetic range is calculated using the formulas
, h - in m, D - in km, R - 6378 km
Where h n and h pr – in meters, D – in kilometers.
For a person of average height, the horizon distance on Earth is about 5 km. For cosmonauts V.A. Shatalov and A.S. Eliseev, who flew on the Soyuz-8 spacecraft, the horizon range at perigee (altitude 205 km) was 1730 km, and at apogee (altitude 223 km) – 1800 km.
For radio waves, refraction is almost independent of wavelength, but in addition to temperature and pressure, it also depends on the water vapor content in the air. Under the same conditions of temperature and pressure changes, radio waves are refracted more strongly than light ones, especially with high humidity.
Therefore, in the formulas for determining the range of the horizon or detecting an object by a radar beam in front of the root there will be a coefficient of 4.08. Consequently, the horizon of the radar system is approximately 11% further away.
Radio waves are well reflected from the earth's surface and from the lower boundary of the inversion or layer of low humidity. In such a unique waveguide formed by the earth's surface and the base of the inversion, radio waves can propagate over very long distances. These features of radio wave propagation are successfully used in radar.
The air temperature in the ground layer, especially in its lower part, does not always fall with height. It can decrease at different rates, it may not change with height (isothermia) and it can increase with height (inversion). Depending on the magnitude and sign of the temperature gradient, refraction can have different effects on the range of the visible horizon.
The vertical temperature gradient in a homogeneous atmosphere in which the air density does not change with height, g 0 = 3.42°C/100m. Let's consider what the ray trajectory will be AB at different temperature gradients at the Earth's surface.
Let , i.e. air temperature decreases with altitude. Under this condition, the refractive index also decreases with height. The trajectory of the light beam in this case will be facing the earth's surface with its concave side (in Fig. 2.9 the trajectory AB¢). This refraction is called positive. Farthest point IN¢ the observer will see in the direction of the last tangent to the ray path. This tangent, i.e. the horizon visible due to refraction is equal to the mathematical horizon NAS angle D, less than angle d. Corner d is the angle between the mathematical and geometric horizon without refraction. Thus, the visible horizon has risen by an angle ( d- D) and expanded because D > D0.
Now let's imagine that g gradually decreases, i.e. Temperature decreases more and more slowly with altitude. There will come a moment when the temperature gradient becomes zero (isothermia), and then the temperature gradient becomes negative. The temperature no longer decreases, but increases with altitude, i.e. temperature inversion is observed. As the temperature gradient decreases and passes through zero, the visible horizon will rise higher and higher and a moment will come when D becomes equal to zero. The visible geodetic horizon will rise to the mathematical one. The earth's surface seemed to straighten out and become flat. The geodetic visibility range is infinitely large. The radius of curvature of the beam became equal to the radius of the globe.
With an even stronger temperature inversion, D becomes negative. The visible horizon has risen above the mathematical one. It will seem to the observer at point A that he is at the bottom of a huge basin. Because of the horizon, objects located far beyond the geodetic horizon rise and become visible (as if floating in the air) (Fig. 2.10).
Such phenomena can be observed in polar countries. So, from the Canadian coast of America through Smith Strait you can sometimes see the coast of Greenland with all the buildings on it. The distance to the Greenland coast is about 70 km, while the geodetic visibility range is no more than 20 km. Another example. From Hastings, on the English side of the Pas-de-Calais Strait, I could see the French coast, lying across the Strait at a distance of about 75 km.
Fig.2.10. The phenomenon of unusual refraction in polar countries
Now let's assume that g=g 0, therefore, the air density does not change with height (homogeneous atmosphere), there is no refraction and D=D 0 .
At g > g 0 the refractive index and air density increase with altitude. In this case, the trajectory of light rays faces the earth's surface with its convex side. This refraction is called negative. The last point on Earth that an observer at A will see will be B². The visible horizon AB² narrowed and dropped to an angle (D - d).
From what has been discussed, we can formulate the following rule: if along the propagation of a light beam in the atmosphere the air density (and, therefore, the refractive index) changes, then the light beam will bend so that its trajectory is always convex in the direction of decreasing the density (and refractive index) of the air .
Refraction and mirages
The word mirage is of French origin and has two meanings: “reflection” and “deceptive vision.” Both meanings of this word well reflect the essence of the phenomenon. A mirage is an image of an object that actually exists on Earth, often enlarged and greatly distorted. There are several types of mirages depending on where the image is located in relation to the object: upper, lower, lateral and complex. The most commonly observed are superior and inferior mirages, which occur when there is an unusual distribution of density (and, therefore, refractive index) in height, when at a certain height or near the surface of the Earth there is a relatively thin layer of very warm air (with a low refractive index), in which Rays coming from ground objects experience total internal reflection. This occurs when rays fall on this layer at an angle greater than the angle of total internal reflection. This warmer layer of air plays the role of an air mirror, reflecting the rays falling into it.
Superior mirages (Fig. 2.11) occur in the presence of strong temperature inversions, when air density and refractive index rapidly decrease with height. In superior mirages, the image is located above the object.
Fig.2.11. Superior Mirage
The trajectories of light rays are shown in Figure (2.11). Let us assume that the earth's surface is flat and layers of equal density are located parallel to it. Since density decreases with height, then . The warm layer, which acts as a mirror, lies at a height. In this layer, when the angle of incidence of the rays becomes equal to the refractive index (), the rays rotate back to the earth's surface. The observer can simultaneously see the object itself (if it is not beyond the horizon) and one or more images above it - upright and inverted.
Fig.2.12. Complex superior mirage
In Fig. Figure 2.12 shows a diagram of the occurrence of a complex upper mirage. The object itself is visible ab, above him there is a direct image of him a¢b¢, inverted in²b² and again direct a²¢b²¢. Such a mirage can occur if the air density decreases with altitude, first slowly, then quickly, and again slowly. The image turns out upside down if the rays coming from the extreme points of the object intersect. If an object is far away (beyond the horizon), then the object itself may not be visible, but its images, raised high in the air, are visible from great distances.
The city of Lomonosov is located on the shores of the Gulf of Finland, 40 km from St. Petersburg. Usually from Lomonosov St. Petersburg is not visible at all or is visible very poorly. Sometimes St. Petersburg is visible “at a glance.” This is one example of superior mirages.
Apparently, the number of upper mirages should include at least part of the so-called ghostly Lands, which were searched for decades in the Arctic and were never found. They searched for Sannikov Land for a particularly long time.
Yakov Sannikov was a hunter and was involved in the fur trade. In 1811 He set off on dogs across the ice to the group of New Siberian Islands and from the northern tip of Kotelny Island saw an unknown island in the ocean. He was unable to reach it, but reported the discovery of a new island to the government. In August 1886 E.V. Tol, during his expedition to the New Siberian Islands, also saw Sannikov Island and wrote in his diary: “The horizon is completely clear. In the direction to the northeast, 14-18 degrees, the contours of four mesas were clearly visible, which connected to the low-lying land in the east. Thus, Sannikov’s message was completely confirmed. We have the right, therefore, to draw a dotted line in the appropriate place on the map and write on it: “Sannikov Land.”
Tol gave 16 years of his life to the search for Sannikov Land. He organized and conducted three expeditions to the New Siberian Islands area. During the last expedition on the schooner “Zarya” (1900-1902), Tolya’s expedition died without finding Sannikov Land. No one saw Sannikov Land again. Perhaps it was a mirage that appears in the same place at certain times of the year. Both Sannikov and Tol saw a mirage of the same island located in this direction, only much further in the ocean. Perhaps it was one of the De Long Islands. Perhaps it was a huge iceberg - an entire ice island. Such ice mountains, with an area of up to 100 km2, travel across the ocean for several decades.
The mirage did not always deceive people. English polar explorer Robert Scott in 1902. in Antarctica I saw mountains as if hanging in the air. Scott suggested that there was a mountain range further beyond the horizon. And, indeed, the mountain range was discovered later by the Norwegian polar explorer Raoul Amundsen exactly where Scott expected it to be located.
Fig.2.13. Inferior Mirage
Inferior mirages (Fig. 2.13) occur with a very rapid decrease in temperature with height, i.e. at very large temperature gradients. The role of an air mirror is played by the thin surface warmest layer of air. A mirage is called an inferior mirage because the image of an object is placed under the object. In lower mirages, it seems as if there is a surface of water under the object and all objects are reflected in it.
In calm water, all objects standing on the shore are clearly reflected. Reflection in a thin layer of air heated from the earth's surface is completely similar to reflection in water, only the role of a mirror is played by the air itself. The air condition in which inferior mirages occur is extremely unstable. After all, below, near the ground, lies highly heated, and therefore lighter, air, and above it lies colder and heavier air. Jets of hot air rising from the ground penetrate layers of cold air. Due to this, the mirage changes before our eyes, the surface of the “water” seems to be agitated. A small gust of wind or a shock is enough and a collapse will occur, i.e. turning over air layers. Heavy air will rush down, destroying the air mirror, and the mirage will disappear. Favorable conditions for the occurrence of inferior mirages are a homogeneous, flat underlying surface of the Earth, which occurs in steppes and deserts, and sunny, windless weather.
If a mirage is an image of a really existing object, then the question arises: what kind of water surface do travelers in the desert see? After all, there is no water in the desert. The fact is that the apparent water surface or lake visible in a mirage is in fact an image not of the water surface, but of the sky. Parts of the sky are reflected in the air mirror and create the complete illusion of a shiny water surface. Such a mirage can be seen not only in the desert or steppe. They even appear in St. Petersburg and its environs on sunny days over asphalt roads or a flat sandy beach.
Fig.2.14. Side mirage
Side mirages occur in cases where layers of air of the same density are located in the atmosphere not horizontally, as usual, but obliquely and even vertically (Fig. 2.14). Such conditions are created in the summer, in the morning shortly after sunrise, on the rocky shores of the sea or lake, when the shore is already illuminated by the Sun, and the surface of the water and the air above it are still cold. Lateral mirages have been repeatedly observed on Lake Geneva. A side mirage can appear near a stone wall of a house heated by the Sun, and even on the side of a heated stove.
Complex types of mirages, or Fata Morgana, occur when there are simultaneously conditions for the appearance of both an upper and lower mirage, for example, during a significant temperature inversion at a certain altitude above a relatively warm sea. Air density first increases with height (air temperature decreases), and then also quickly decreases (air temperature rises). With such a distribution of air density, the state of the atmosphere is very unstable and subject to sudden changes. Therefore, the appearance of the mirage changes before our eyes. The most ordinary rocks and houses, due to repeated distortions and magnification, turn into the wonderful castles of the fairy Morgana before our eyes. Fata Morgana is observed off the coast of Italy and Sicily. But it can also occur at high latitudes. This is how the famous Siberian explorer F.P. Wrangel described the Fata Morgana he saw in Nizhnekolymsk: “The action of horizontal refraction produced a kind of Fata Morgana. The mountains lying to the south seemed to us in various distorted forms and hanging in the air. The distant mountains seemed to have their peaks overturned. The river narrowed to the point that the opposite bank seemed to be almost at our huts.”
Have you ever wondered why the stars are not visible in the sky during the daytime? After all, the air is as transparent during the day as it is at night. The whole point here is that during the daytime the atmosphere scatters sunlight.
Imagine that you are in a well-lit room in the evening. Through the window glass, bright lights located outside are visible quite clearly. But dimly lit objects are almost impossible to see. However, as soon as you turn off the light in the room, the glass ceases to serve as an obstacle to our vision.
Something similar happens when observing the sky: during the day, the atmosphere above us is brightly illuminated and the Sun is visible through it, but the weak light of distant stars cannot penetrate. But after the Sun sinks below the horizon and the sunlight (and with it the light scattered by the air) “turns off,” the atmosphere becomes “transparent” and the stars can be observed.
It's a different matter in space. As the spacecraft rises to altitude, dense layers of the atmosphere remain below and the sky gradually darkens.
At an altitude of about 200-300 km, where manned spacecraft usually fly, the sky is completely black. It is always black, even if the Sun is currently on the visible part of it.
“The sky is completely black. The stars in this sky look somewhat brighter and are more clearly visible against the background of the black sky,” this is how the first cosmonaut Yu. A. Gagarin described his space impressions.
But still, even from the spacecraft on the day side of the sky, not all the stars are visible, but only the brightest. The eye is disturbed by the blinding light of the Sun and the light of the Earth.
If we look at the sky from Earth, we will clearly see that all the stars are twinkling. They seem to fade, then flare up, shimmering with different colors. And the lower the star is located above the horizon, the stronger the flickering.
The twinkling of stars is also explained by the presence of an atmosphere. Before reaching our eyes, the light emitted by a star passes through the atmosphere. In the atmosphere there are always masses of warmer and colder air. Its Density depends on the temperature of the air in a particular area. Passing from one area to another, light rays experience refraction. The direction of their propagation changes. Due to this, in some places above the earth's surface they are concentrated, in others they are relatively rare. As a result of the constant movement of air masses, these zones are constantly shifting, and the observer sees either an increase or decrease in the brightness of the stars. But since different colored rays are not refracted equally, the moments of intensification and weakening of different colors do not occur simultaneously.
In addition, other, more complex optical effects can play a certain role in the twinkling of stars.
The presence of warm and cold layers of air and intense movements of air masses also affect the quality of telescopic images.
Where are the best conditions for astronomical observations: in the mountains or on the plains, on the seashore or inland, in the forest or in the desert? And in general, what is better for astronomers - ten cloudless nights over the course of a month or just one clear night, but one when the air is perfectly clear and calm?
This is only a small part of the issues that have to be resolved when choosing a location for the construction of observatories and the installation of large telescopes. A special field of science deals with such problems - astro-climatology.
Of course, the best conditions for astronomical observations are outside the dense layers of the atmosphere, in space. By the way, the stars here do not twinkle, but burn with a cold, calm light.
Familiar constellations look exactly the same in space as they do on Earth. The stars are at enormous distances from us, and moving away from the earth's surface by a few hundred kilometers cannot change anything in their apparent relative position. Even when observed from Pluto, the outlines of the constellations would be exactly the same.
During one orbit from a spacecraft moving in low-Earth orbit, in principle, you can see all the constellations of the earth's sky. Observing stars from space is of dual interest: astronomical and navigational. In particular, it is very important to observe starlight unmodified by the atmosphere.
Navigation by the stars is no less important in space. By observing pre-selected “reference” stars, you can not only orient the ship, but also determine its position in space.
For a long time, astronomers have dreamed of future observatories on the surface of the Moon. It seemed that the complete absence of an atmosphere should create ideal conditions on the Earth’s natural satellite for astronomical observations both during the lunar night and during the lunar day.
There is a lot of interesting things in the world. The twinkling of stars is one of the most amazing phenomena. How many different beliefs are associated with this phenomenon! The unknown always frightens and attracts at the same time. What is the nature of this phenomenon?
Influence of the atmosphere
Astronomers have made an interesting discovery: the twinkling of stars has nothing to do with their changes. Then why do stars twinkle in the night sky? It's all about the atmospheric movement of cold and hot air flows. Where warm layers pass over cold ones, air vortices are formed. Under the influence of these vortices, the rays of light are distorted. This is how light rays bend, changing the apparent position of stars.
An interesting fact is that the stars do not twinkle at all. This vision is created on earth. Observers' eyes perceive light coming from a star after it passes through the atmosphere. Therefore, to the question of why stars twinkle, we can answer that stars do not twinkle, but the phenomenon that we observe on earth is a distortion of light that has passed from a star through the atmospheric layers of air. If such air movements did not occur, then flickering would not be observed, even from the most distant star in space.
Scientific explanation
If we expand on the question of why stars twinkle in more detail, it is worth noting that this process is observed when light from a star moves from a denser atmospheric layer to a less dense one. In addition, as mentioned above, these layers are constantly moving relative to each other. From the laws of physics we know that warm air rises, and cold air, on the contrary, sinks. It is when light passes this layer boundary that we observe flickering.
Passing through layers of air of different density, the light of the stars begins to flicker, and their outlines blur and the image increases. At the same time, the radiation intensity and, accordingly, brightness also change. Thus, by studying and observing the processes described above, scientists understood why stars twinkle, and their flickering varies in intensity. In science, this change in light intensity is called scintillation.
Planets and stars: what's the difference?
Another interesting fact is that not every luminous cosmic object produces light emanating from the phenomenon of scintillation. Let's take the planets. They also reflect sunlight, but do not flicker. It is by the nature of radiation that a planet is distinguished from a star. Yes, the light of a star flickers, but the light of a planet does not.
Since ancient times, humanity has learned to navigate in space using the stars. In those days when precision instruments were not invented, the sky helped to find the right path. And today this knowledge has not lost its significance. Astronomy as a science began in the 16th century, when the telescope was first invented. That’s when they began to closely observe the light of the stars and study the laws by which they twinkle. Word astronomy translated from Greek it is “the law of the stars.”
Star Science
Astronomy studies the Universe and celestial bodies, their movement, location, structure and origin. Thanks to the development of science, astronomers have explained how a twinkling star in the sky differs from a planet, how the development of celestial bodies, their systems, and satellites occurs. This science has looked far beyond the boundaries of the solar system. Pulsars, quasars, nebulae, asteroids, galaxies, black holes, interstellar and interplanetary matter, comets, meteorites and everything related to outer space are studied by the science of astronomy.
The intensity and color of the twinkling starlight is also influenced by the altitude of the atmosphere and proximity to the horizon. It is easy to notice that stars located close to it shine brighter and shimmer in different colors. This sight becomes especially beautiful on frosty nights or immediately after rain. At these moments the sky is cloudless, which contributes to a brighter flicker. Sirius has a special radiance.
Atmosphere and starlight
If you want to observe the twinkling of stars, you should understand that with a calm atmosphere at the zenith, this is only possible occasionally. The brightness of the light flux is constantly changing. This is again due to the deflection of light rays, which are unevenly concentrated above the earth's surface. The wind also influences the starscape. In this case, the observer of the star panorama constantly finds himself alternately in a darkened or illuminated area.
When observing stars located at an altitude of more than 50°, the color change will not be noticeable. But stars that are below 35° will twinkle and change color quite often. Very intense flickering indicates atmospheric heterogeneity, which is directly related to meteorology. While observing stellar twinkling, it was noticed that it tends to intensify at low atmospheric pressure and temperature. An increase in flicker can also be noticed with increasing humidity. However, it is impossible to predict the weather using scintillation. The state of the atmosphere depends on a large number of different factors, which makes it impossible to draw conclusions about the weather based solely on stellar twinkling. Of course, some things work, but this phenomenon still has its own ambiguities and mysteries.
THE GOVERNMENT OF MOSCOW
MOSCOW DEPARTMENT OF EDUCATION
EASTERN DISTRICT DEPARTMENT
STATE BUDGET EDUCATIONAL INSTITUTION
SECONDARY SCHOOL No. 000
111141 Moscow st. Perovskaya building 44-a, building 1,2 Telephone
Lesson No. 5 (02/28/13)
"Work with text"
Examination materials in physics include tasks that test students’ ability to master information that is new to them, work with this information, and answer questions, the answers to which follow from the text proposed for study. After studying the text, three tasks are offered (No. 16,17 - basic level, No. 18 - advanced level).
Gilbert's experiments on magnetism.
Gilbert cut a ball out of a natural magnet so that it had poles at two diametrically opposite points. He called this spherical magnet a terella (Fig. 1), that is, a small Earth. By bringing a moving magnetic needle closer to it, you can clearly show the various positions of the magnetic needle that it takes at different points on the earth's surface: at the equator, the needle is located parallel to the horizon plane, at the pole - perpendicular to the horizon plane.
Let us consider an experiment that reveals “magnetism through influence.” Let's hang two iron strips parallel to each other on threads and slowly bring a large permanent magnet towards them. In this case, the lower ends of the strips diverge, since they are magnetized equally (Fig. 2a). As the magnet approaches further, the lower ends of the strips converge somewhat, since the pole of the magnet itself begins to act on them with greater force (Fig. 2b).
Task 16
How does the angle of inclination of the magnetic needle change as it moves across the globe along the meridian from the equator to the pole?
1) increases all the time
2) decreases all the time
3) first increases, then decreases
4) first decreases, then increases
Correct answer: 1
Task 17
At what points are the magnetic poles of the terella located (Fig. 1)?
Correct answer: 2
Task 18
In an experiment revealing "magnetism through influence", both iron strips are magnetized. In Figures 2a and 2b, the poles of the left strip are indicated for both cases.
At the lower end of the right stripe
1) in both cases the south pole appears
2) in both cases the north pole appears
3) in the first case the northern one arises, and in the second the southern one arises
4) in the first case the southern one arises, and in the second the northern one arises
Correct answer: 2
Ptolemy's experiments on the refraction of light.
Greek astronomer Claudius Ptolemy (c. 130 AD) is the author of a remarkable book that served as the primary textbook on astronomy for nearly 15 centuries. However, in addition to the astronomical textbook, Ptolemy also wrote the book “Optics”, in which he outlined the theory of vision, the theory of flat and spherical mirrors and a study of the phenomenon of light refraction.
Ptolemy encountered the phenomenon of light refraction while observing the stars. He noticed that a ray of light, moving from one medium to another, “breaks.” Therefore, a star ray, passing through the earth’s atmosphere, reaches the earth’s surface not in a straight line, but along a curved line, that is, refraction occurs. The curvature of the beam occurs due to the fact that the air density changes with altitude.
To study the law of refraction, Ptolemy conducted the following experiment..gif" width="13" height="24 src="> (see figure). The rulers could rotate around the center of the circle on a common axis O.
Ptolemy immersed this circle in water to the diameter AB and, turning the lower ruler, ensured that the rulers lay on the same straight line for the eye (if you look along the upper ruler). After that, he took the circle out of the water and compared the angles of incidence α and refraction β . It measured angles with an accuracy of 0.5°. The numbers obtained by Ptolemy are presented in the table.
Angle of incidence α , hail | ||||||||
Angle of refraction β , hail |
Ptolemy did not find a “formula” for the relationship between these two series of numbers. However, if we determine the sines of these angles, it turns out that the ratio of the sines is expressed by almost the same number, even with such a rough measurement of angles, which Ptolemy resorted to.
Task 16
In the text, refraction refers to the phenomenon
1) changes in the direction of propagation of the light beam due to reflection at the boundary of the atmosphere
2) changes in the direction of propagation of a light beam due to refraction in the Earth’s atmosphere
3) absorption of light as it propagates in the Earth’s atmosphere
4) bending of the light beam around obstacles and, thereby, deviation from rectilinear propagation
Correct answer: 2
Task 17
Which of the following conclusions contradicts Ptolemy's experiments?
1) the angle of refraction is less than the angle of incidence when the beam passes from air to water
2) with increasing angle of incidence, the angle of refraction increases linearly
3) the ratio of the sine of the angle of incidence to the sine of the angle of refraction does not change
4) the sine of the angle of refraction depends linearly on the sine of the angle of incidence
Correct answer: 2
Task 18
Due to the refraction of light in a calm atmosphere, the apparent position of stars in the sky relative to the horizon
1) above the actual position
2) below the actual position
3) shifted to one side or another vertically relative to the actual position
4) coincides with the actual position
Correct answer: 1
Thomson's experiments and the discovery of the electron
At the end of the 19th century, many experiments were carried out to study electric discharge in rarefied gases. The discharge was excited between the cathode and anode, sealed inside a glass tube from which the air was evacuated. What came from the cathode was called cathode rays.
To determine the nature of cathode rays, the English physicist Joseph John Thomson (1856 - 1940) conducted the following experiment. His experimental setup was a vacuum cathode ray tube (see figure). The heated cathode K was a source of cathode rays, which were accelerated by the electric field existing between anode A and cathode K. There was a hole in the center of the anode. The cathode rays passing through this hole hit point G on the wall of the tube S opposite the hole in the anode. If wall S is covered with a fluorescent substance, then the rays hitting point G will appear as a luminous spot. On the way from A to G, the rays passed between the plates of a capacitor CD, to which voltage from a battery could be applied.
If you turn on this battery, the rays are deflected by the electric field of the capacitor and a spot appears on the screen S at position . Thomson proposed that cathode rays behave like negatively charged particles. By creating in the area between the capacitor plates a uniform magnetic field perpendicular to the plane of the picture (it is depicted by dots), you can cause the speck to deflect in the same or opposite direction.
Experiments have shown that the charge of the particle is equal in magnitude to the charge of the hydrogen ion (C), and its mass turns out to be almost 1840 times less than the mass of the hydrogen ion.
Later it received the name electron. The day April 30, 1897, when Joseph John Thomson reported on his research, is considered the “birthday” of the electron.
Task 16
What are cathode rays?
1) X-rays
2) gamma rays
3) electron flow
4) ion flow
Correct answer: 3
Task 17
A. Cathode rays interact with the electric field.
B. Cathode rays interact with a magnetic field.
1) only A
2) only B
4) neither A nor B
Correct answer: 3
Task 18
The cathode rays (see figure) will hit point G provided that between the plates of the capacitor CD
1) only the electric field acts
2) only the magnetic field acts
3) the action of forces from the electric and magnetic fields is compensated
4) the effect of forces from the magnetic field is negligible
Correct answer: 3
Experimental discovery of the law of equivalence of heat and work.
In 1807, the physicist J. Gay-Lussac, who studied the properties of gases, performed a simple experiment. It has long been known that compressed gas, expanding, cools. Gay-Lussac forced the gas to expand into emptiness - into a vessel from which the air had previously been pumped out. To his surprise, no decrease in temperature occurred; the temperature of the gas did not change. The researcher could not explain the result: why does the same gas, equally compressed, expand, cool if it is released directly outside into the atmosphere, and not cool if it is released into an empty vessel where the pressure is zero?
The German doctor Robert Mayer was able to explain the experience. Mayer had the idea that work and heat could be transformed into one another. This wonderful idea immediately made it possible for Mayer to make clear the mysterious result in the Gay-Lussac experiment: if heat and work are mutually converted, then when a gas expands into emptiness, when it does not do any work, since there is no force (pressure) opposing its increase volume, the gas should not be cooled. If, when a gas expands, it has to do work against external pressure, its temperature should decrease. You can't get a job for nothing! Mayer's remarkable result has been confirmed many times by direct measurements; Of particular importance were the experiments of Joule, who measured the amount of heat required to heat a liquid by rotating a stirrer in it. At the same time, both the work expended on rotating the mixer and the amount of heat received by the liquid were measured. No matter how the experimental conditions changed, different liquids, different vessels and mixers were taken, the result was the same: the same amount of heat was always obtained from the same work.
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Melting curve (p - pressure, T - temperature)
According to modern ideas, most of the earth's interior remains solid. However, the substance of the asthenosphere (the shell of the Earth from 100 km to 300 km in depth) is in an almost molten state. This is the name for a solid state that easily turns into a liquid (molten) with a slight increase in temperature (process 1) or decrease in pressure (process 2).
The source of primary magma melts is the asthenosphere. If pressure decreases in some area (for example, when sections of the lithosphere are displaced), then the solid matter of the asthenosphere immediately turns into a liquid melt, i.e., into magma.
But what physical reasons set in motion the mechanism of a volcanic eruption?
Magma, along with water vapor, contains various gases (carbon dioxide, hydrogen chloride and fluoride, sulfur oxides, methane and others). The concentration of dissolved gases corresponds to external pressure. In physics, Henry's law is known: the concentration of a gas dissolved in a liquid is proportional to its pressure above the liquid. Now imagine that the pressure at depth has decreased. Gases dissolved in magma become gaseous. The magma increases in volume, foams and begins to rise upward. As the magma rises, the pressure drops even more, so the process of gas release intensifies, which, in turn, leads to an acceleration of the rise.
Task 16
In what states of aggregation is the asthenosphere matter in regions I and II on the diagram (see figure)?
1) I – in liquid, II – in solid
2) I – in solid, II – in liquid
3) I – in liquid, II – in liquid
4) I – in solid, II – in solid
Correct answer: 2
Task 17
What force causes molten, foaming magma to rise upward?
1) gravity
2) elastic force
3) Archimedes' force
4) friction force
Correct answer: 3
Task 18
Caisson sickness is a disease that occurs when a diver quickly rises from great depths. Caisson disease occurs in humans when there is a rapid change in external pressure. When working under conditions of increased pressure, human tissues absorb additional amounts of nitrogen. Therefore, scuba divers must ascend slowly so that the blood has time to carry the resulting gas bubbles into the lungs.
Which statements are true?
A. The concentration of nitrogen dissolved in the blood increases the deeper the diver dives.
B. During an excessively rapid transition from a high-pressure environment to a low-pressure environment, excess nitrogen dissolved in the tissues is released, forming gas bubbles.
1) only A
2) only B
4) neither A nor B
Correct answer: 3
Geysers
Geysers are located near active or recently dormant volcanoes. Geysers require heat from volcanoes to erupt.
To understand the physics of geysers, recall that the boiling point of water depends on pressure (see figure).
Dependence of the boiling point of water on pressure https://pandia.ru/text/78/089/images/image013_71.gif" width="25" height="21"> Pa. In this case, the water in the tube
1) will move downward under the influence of atmospheric pressure
2) will remain in equilibrium, since its temperature is below the boiling point
3) will cool quickly, since its temperature is below the boiling point at a depth of 10 m
4) will boil, since its temperature is higher than the boiling point at external pressure Pa
Correct answer: 4
Fog
Under certain conditions, water vapor in the air partially condenses, resulting in water droplets of fog. Water droplets have a diameter from 0.5 microns to 100 microns.
Take a vessel, fill it halfway with water and close the lid. The fastest water molecules, overcoming the attraction from other molecules, jump out of the water and form steam above the surface of the water. This process is called water evaporation. On the other hand, water vapor molecules, colliding with each other and with other air molecules, can randomly end up at the surface of the water and turn back into liquid. This is steam condensation. Ultimately, at a given temperature, the processes of evaporation and condensation are mutually compensated, that is, a state of thermodynamic equilibrium is established. The water vapor located in this case above the surface of the liquid is called saturated.
If the temperature is increased, the rate of evaporation increases and equilibrium is established at a higher density of water vapor. Thus, the density of saturated vapor increases with increasing temperature (see figure).
Dependence of saturated water vapor density on temperature
For fog to occur, the steam must become not just saturated, but supersaturated. Water vapor becomes saturated (and supersaturated) with sufficient cooling (AB process) or during additional evaporation of water (AC process). Accordingly, the falling fog is called cooling fog and evaporation fog.
The second condition necessary for the formation of fog is the presence of condensation nuclei (centers). The role of nuclei can be played by ions, tiny droplets of water, dust particles, soot particles and other small contaminants. The more air pollution, the denser the fog.
Task 16
The graph in the figure shows that at a temperature of 20 °C the density of saturated water vapor is 17.3 g/m3. This means that at 20 °C
5) in 1 m the mass of saturated water vapor is 17.3 g
6) 17.3 m of air contains 1 g of saturated water vapor
8) air density is 17.3 g/m
Correct answer: 1
Task 17
In which process shown on the graph can evaporation fog be observed?
1) AB only
2) only AC
4) neither AB nor AC
Correct answer: 2
Task 18
Which statements are true?
A. Urban fogs, compared to fogs in mountainous areas, are characterized by a higher density.
B. Fogs are observed when the air temperature rises sharply.
1) only A
2) only B
4) neither A nor B
Correct answer: 1
The color of the sky and the setting sun
Why is the sky blue? Why does the setting Sun turn red? It turns out that in both cases the reason is the same - the scattering of sunlight in the earth's atmosphere.
In 1869, the English physicist J. Tyndall performed the following experiment: a weakly diverging narrow beam of light was passed through a rectangular aquarium filled with water. It was noted that if you look at the light beam in the aquarium from the side, it appears bluish. And if you look at the beam from the output end, the light takes on a reddish tint. This can be explained by assuming that blue (blue) light is scattered more than red light. Therefore, when a white light beam passes through a scattering medium, mainly blue light is scattered from it, so that red light begins to predominate in the beam emerging from the medium. The further a white beam travels in a scattering medium, the redder it appears at the exit.
In 1871, J. Strett (Rayleigh) developed a theory of scattering of light waves by small particles. The law established by Rayleigh states: the intensity of scattered light is proportional to the fourth power of the frequency of light or, in other words, inversely proportional to the fourth power of the light wavelength.
Rayleigh put forward a hypothesis according to which the centers that scatter light are air molecules. Later, already in the first half of the 20th century, it was established that the main role in light scattering is played by air density fluctuations - microscopic condensations and rarefactions of air that arise as a result of the chaotic thermal movement of air molecules.
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The disc on which the sound is recorded is made of a special soft wax material. A copper copy (cliché) is removed from this wax disk using a galvanoplastic method. This involves the deposition of pure copper on an electrode when an electric current passes through a solution of its salts. The copper copy is then imprinted onto plastic discs. This is how gramophone records are made.
When playing sound, a gramophone record is placed under a needle connected to the gramophone membrane, and the record is rotated. Moving along the wavy groove of the record, the end of the needle vibrates, and the membrane vibrates along with it, and these vibrations quite accurately reproduce the recorded sound.
Task 16
What vibrations does the horn membrane make under the influence of a sound wave?
5) free
6) fading
7) forced
8) self-oscillations
Correct answer: 3
Task 17
What current action is used to obtain a cliché from a wax disk?
1) magnetic
2) thermal
3) light
4) chemical
Correct answer: 4
Task 18
When recording sound mechanically, a tuning fork is used. By increasing the playing time of the tuning fork by 2 times
5) the length of the sound groove will increase by 2 times
6) the length of the sound groove will decrease by 2 times
7) the depth of the sound groove will increase by 2 times
8) the depth of the sound groove will decrease by 2 times
Correct answer: 1
Magnetic suspension
The average speed of trains on railways does not exceed
150 km/h. Designing a train that can match the speed of an airplane is not easy. At high speeds, train wheels cannot withstand the load. There is only one way out: to abandon the wheels, making the train fly. One way to "suspend" a train above the tracks is to use magnetic repulsion.
In 1910, the Belgian E. Bachelet built the world's first model of a flying train and tested it. The 50-kilogram cigar-shaped carriage of the flying train accelerated to speeds of over 500 km/h! Bachelet's magnetic road was a chain of metal posts with coils attached to their tops. After turning on the current, the trailer with built-in magnets was raised above the coils and accelerated by the same magnetic field over which it was suspended.
Almost simultaneously with Bachelet in 1911, professor of the Tomsk Institute of Technology B. Weinberg developed a much more economical suspension for a flying train. Weinberg proposed not to push the road and the cars away from each other, which is fraught with enormous energy costs, but to attract them with ordinary electromagnets. The electromagnets of the road were located above the train in order to compensate for the gravity of the train with their attraction. The iron car was initially located not exactly under the electromagnet, but behind it. In this case, electromagnets were mounted along the entire length of the road. When the current in the first electromagnet was turned on, the trailer rose and moved forward, towards the magnet. But a moment before the trailer was supposed to stick to the electromagnet, the current was turned off. The train continued to fly by inertia, reducing its altitude. The next electromagnet turned on, the train rose again and accelerated. By placing his car in a copper pipe from which the air was pumped out, Weinberg accelerated the car to a speed of 800 km/h!
Task 16
Which magnetic interaction can be used for maglev?
A. Attraction of opposite poles.
B. Repulsion of like poles.
1) only A
2) only B
3) neither A nor B
Correct answer: 4
Task 17
When a maglev train moves
1) there are no friction forces between the train and the road
2) air resistance forces are negligible
3) electrostatic repulsion forces are used
4) the attractive forces of magnetic poles of the same name are used
Correct answer: 1
Task 18
In B. Weinberg's model of a magnetic train, it was necessary to use a trailer with a larger mass. In order for the new trailer to move as before, it is necessary
5) replace the copper pipe with an iron one
6) do not turn off the current in the electromagnets until the trailer “sticks”
7) increase the current in the electromagnets
8) install electromagnets along the length of the road at large intervals
Correct answer: 3
Piezoelectricity
In 1880, French scientists brothers Pierre and Paul Curie investigated the properties of crystals. They noticed that if a quartz crystal is compressed from both sides, then electric charges appear on its faces perpendicular to the direction of compression: positive on one face, negative on the other. Crystals of tourmaline, Rochelle salt, and even sugar have the same property. Charges on the crystal faces also arise when it is stretched. Moreover, if during compression a positive charge accumulated on the face, then during tension a negative charge will accumulate on this face, and vice versa. This phenomenon was called piezoelectricity (from the Greek word "piezo" - press). A crystal with this property is called a piezoelectric. Later, the Curie brothers discovered that the piezoelectric effect is reversible: if opposite electric charges are created on the faces of a crystal, it will either shrink or stretch, depending on which face a positive and negative charge is applied to.
The action of widespread piezoelectric lighters is based on the phenomenon of piezoelectricity. The main part of such a lighter is a piezoelectric element - a ceramic piezoelectric cylinder with metal electrodes on the bases. Using a mechanical device, a short-term shock is applied to the piezoelectric element. In this case, opposite electric charges appear on its two sides, located perpendicular to the direction of action of the deforming force. The voltage between these sides can reach several thousand volts. The voltage is supplied via insulated wires to two electrodes located in the tip of the lighter at a distance of 3 - 4 mm from each other. The spark discharge that occurs between the electrodes ignites the mixture of gas and air.
Despite the very high voltages (~10 kV), experiments with a piezo lighter are completely safe, since even with a short circuit the current strength turns out to be negligible and safe for human health, as with electrostatic discharges when removing woolen or synthetic clothing in dry weather.
Task 16
Piezoelectricity is a phenomenon
1) the appearance of electric charges on the surface of crystals during their deformation
2) the occurrence of tensile and compressive deformation in crystals
3) passing electric current through the crystals
4) passage of a spark discharge during crystal deformation
Correct answer: 1
Task 17
Using a piezo lighter doesn't represent dangers because
7) the current strength is negligible
8) a current of 1 A is safe for humans
Correct answer: 3
Task 18
At the beginning of the 20th century, French scientist Paul Langevin invented an ultrasonic wave emitter. By charging the faces of a quartz crystal with electricity from a high-frequency alternating current generator, he found that the crystal oscillates at the frequency of the voltage change. The action of the emitter is based on
1) direct piezoelectric effect
2) inverse piezoelectric effect
3) the phenomenon of electrification under the influence of an external electric field
4) the phenomenon of electrification upon impact
Correct answer: 2
Construction of the Egyptian pyramids
The Pyramid of Cheops is one of the Seven Wonders of the World. There are still many questions about how exactly the pyramid was built.
Transporting, lifting and installing stones weighing tens and hundreds of tons was not an easy task.
In order to lift the stone blocks up, they came up with a very cunning method. Earthen ramps were erected around the construction site. As the pyramid grew, the ramps rose higher and higher, as if encircling the entire future building. Stones were dragged along the ramp on sleds in the same way as on the ground, helping themselves with levers. The angle of inclination of the ramp was very small - 5 or 6 degrees, because of this the length of the ramp grew to hundreds of meters. Thus, during the construction of the Pyramid of Khafre, the ramp connecting the upper temple with the lower one, with a difference in levels of more than 45 m, had a length of 494 m and a width of 4.5 m.
In 2007, French architect Jean-Pierre Houdin suggested that during the construction of the Cheops pyramid, ancient Egyptian engineers used a system of both external and internal ramps and tunnels. Houdin believes that only the lower one was built with the help of external ramps,
43-meter part (the total height of the Cheops pyramid is 146 meters). To lift and install the remaining blocks, a system of internal ramps arranged in a spiral was used. To do this, the Egyptians dismantled the external ramps and moved them inside. The architect is confident that the cavities discovered in 1986 in the thickness of the Cheops pyramid are tunnels into which ramps gradually turned.
Task 16
What type of simple mechanisms is a ramp?
5) moving block
6) fixed block
8) inclined plane
Correct answer: 4
Task 17
Ramps include
5) freight elevator in residential buildings
6) crane boom
7) gate for raising water from the well
8) an inclined platform for vehicles to enter
Correct answer: 4
Task 18
If we neglect friction, then the ramp that connected the upper temple with the lower one during the construction of the Pyramid of Khafre made it possible to obtain a gain
5) about 11 times stronger
6) More than 100 times strength
7) in operation approximately 11 times
8) at a distance of approximately 11 times
Correct answer: 1
Albedo of the Earth
The temperature at the Earth's surface depends on the reflectivity of the planet - albedo. Surface albedo is the ratio of the energy flux of reflected solar rays to the energy flux of solar rays incident on the surface, expressed as a percentage or fraction of a unit. The Earth's albedo in the visible part of the spectrum is about 40%. In the absence of clouds it would be about 15%.
Albedo depends on many factors: the presence and condition of cloudiness, changes in glaciers, time of year, and, accordingly, precipitation. In the 90s of the 20th century, the significant role of aerosols - the smallest solid and liquid particles in the atmosphere - became obvious. When fuel is burned, gaseous sulfur and nitrogen oxides are released into the air; combining in the atmosphere with water droplets, they form sulfuric, nitric acids and ammonia, which then turn into sulfate and nitrate aerosols. Aerosols not only reflect sunlight, preventing it from reaching the Earth's surface. Aerosol particles serve as condensation nuclei for atmospheric moisture during cloud formation and thereby contribute to an increase in cloudiness. And this, in turn, reduces the flow of solar heat to the earth's surface.
Transparency to sunlight in the lower layers of the earth's atmosphere also depends on fires. Due to fires, dust and soot rise into the atmosphere, which cover the Earth with a dense screen and increase the albedo of the surface.
Task 16
Surface albedo refers to
1) the total flux of solar rays incident on the Earth’s surface
2) the ratio of the energy flux of reflected radiation to the flux of absorbed radiation
3) the ratio of the energy flux of reflected radiation to the flux of incident radiation
4) the difference between the incident and reflected radiation energy
Correct answer: 3
Task 17
Which statements are true?
A. Aerosols reflect sunlight and thereby help reduce the Earth's albedo.
B. Volcanic eruptions increase the Earth's albedo.
1) only A
2) only B
4) neither A nor B
Correct answer: 2
Task 18
The table shows some characteristics for the planets of the solar system - Venus and Mars. It is known that the albedo of Venus is A = 0.76, and the albedo of Mars is A = 0.15. Which of the characteristics mainly influenced the difference in the albedo of the planets?
Characteristics | Venus | Mars |
A. Average distance from the Sun, in radii of the Earth's orbit | ||
B. Average radius of the planet, km | ||
IN. Number of satellites | ||
G. Presence of atmosphere | very dense | sparse |
Correct answer: 4
Greenhouse effect
To determine the temperature of an object heated by the Sun, it is important to know its distance from the Sun. The closer a planet in the solar system is to the Sun, the higher its average temperature. For an object as distant from the Sun as the Earth, a numerical estimate of the average surface temperature gives the following result: T Å ≈ –15°C.
In reality, the Earth's climate is much milder. Its average surface temperature is about 18 °C due to the so-called greenhouse effect - heating of the lower part of the atmosphere by radiation from the Earth's surface.
The lower layers of the atmosphere are dominated by nitrogen (78%) and oxygen (21%). The remaining components account for only 1%. But it is precisely this percentage that determines the optical properties of the atmosphere, since nitrogen and oxygen almost do not interact with radiation.
The “greenhouse” effect is known to everyone who has dealt with this simple garden structure. In the atmosphere it looks like this. Part of the solar radiation that is not reflected from the clouds passes through the atmosphere, which acts as glass or film, and heats the earth's surface. The heated surface cools down, emitting thermal radiation, but this is a different radiation - infrared. The average wavelength of such radiation is much longer than that coming from the Sun, and therefore the atmosphere, almost transparent to visible light, transmits infrared radiation much less well.
Water vapor absorbs about 62% of infrared radiation, which contributes to heating of the lower layers of the atmosphere. Following water vapor on the list of greenhouse gases is carbon dioxide (CO2), which absorbs 22% of the Earth's infrared radiation in clear air.
The atmosphere absorbs the flow of long-wave radiation rising from the planet's surface, heats up and, in turn, heats the Earth's surface. The maximum in the solar radiation spectrum occurs at a wavelength of about 550 nm. The maximum in the Earth's radiation spectrum occurs at a wavelength of approximately 10 microns. The role of the greenhouse effect is illustrated in Figure 1.
Fig.1(a). Curve 1 - calculated spectrum of solar radiation (with a photosphere temperature of 6000°C); curve 2 - calculated spectrum of the Earth's radiation (with a surface temperature of 25°C)
Fig.1 (b). Absorption (in percentage terms) of radiation at different wavelengths by the earth's atmosphere. In the spectral region from 10 to 20 µm there are absorption bands of CO2, H2O, O3, CH4 molecules. They absorb radiation coming from the surface of the Earth
Task 16
Which gas plays the largest role in the greenhouse effect of the Earth's atmosphere?
10) oxygen
11) carbon dioxide
12) water vapor
Correct answer: 4
Task 17
Which of the following statements corresponds to the curve in Figure 1(b)?
A. Visible radiation, corresponding to the maximum of the solar spectrum, passes through the atmosphere almost unimpeded.
B. Infrared radiation with a wavelength exceeding 10 microns practically does not pass beyond the Earth's atmosphere.
5) only A
6) only B
8) neither A nor B
Correct answer: 3
Task 18
Thanks to the greenhouse effect
1) in cold cloudy weather, woolen clothing protects the human body from hypothermia
2) tea in a thermos remains hot for a long time
3) the sun's rays passing through the glass windows heat the air in the room
4) on a sunny summer day, the water temperature in reservoirs is lower than the temperature of the sand on the shore
Correct answer: 3
Human hearing
The lowest tone perceived by a person with normal hearing has a frequency of about 20 Hz. The upper limit of auditory perception varies greatly between individuals. Age is of particular importance here. At the age of eighteen, with perfect hearing, you can hear sound up to 20 kHz, but on average the limits of audibility for any age lie in the range of 18 - 16 kHz. With age, the sensitivity of the human ear to high-frequency sounds gradually decreases. The figure shows a graph of the level of sound perception versus frequency for people of different ages.
Soreness" href="/text/category/boleznennostmz/" rel="bookmark">painful reactions. Transport or industrial noise has a depressing effect on a person - it tires, irritates, interferes with concentration. As soon as such noise stops, a person experiences a feeling of relief and peace .
A noise level of 20–30 decibels (dB) is practically harmless to humans. This is a natural background noise, without which human life is impossible. For “loud sounds” the maximum permissible limit is approximately 80–90 decibels. A sound of 120–130 decibels already causes pain in a person, and at 150 it becomes unbearable for him. The effect of noise on the body depends on age, hearing sensitivity, and duration of action.
Long periods of continuous exposure to high-intensity noise are most harmful to hearing. After exposure to strong noise, the normal threshold of auditory perception noticeably increases, that is, the lowest level (loudness) at which a given person can still hear a sound of a particular frequency. Measurements of auditory perception thresholds are carried out in specially equipped rooms with a very low level of ambient noise, using sound signals through headphones. This technique is called audiometry; it allows you to obtain a curve of individual hearing sensitivity, or audiogram. Typically, audiograms show deviations from normal hearing sensitivity (see figure).
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Noise source
Noise level (dB)
A. working vacuum cleaner
B. noise in the subway car
IN. pop music orchestra
G. automobile
D. whisper at a distance of 1 m
8) B, B, D and A
Correct answer: 1
Greek astronomer Claudius Ptolemy (c. 130 AD) is the author of a remarkable book that served as the primary textbook on astronomy for nearly 15 centuries. However, in addition to the astronomical textbook, Ptolemy also wrote the book “Optics”, in which he outlined the theory of vision, the theory of flat and spherical mirrors and the study of the phenomenon of light refraction. Ptolemy encountered the phenomenon of light refraction while observing the stars. He noticed that a ray of light, moving from one medium to another, “breaks.” Therefore, a star ray, passing through the earth’s atmosphere, reaches the earth’s surface not in a straight line, but along a curved line, that is, refraction occurs. The curvature of the beam occurs due to the fact that the air density changes with altitude.
To study the law of refraction, Ptolemy conducted the following experiment. He took a circle and fixed the rulers l1 and l2 on the axis so that they could rotate freely around it (see figure). Ptolemy immersed this circle in water to the diameter AB and, turning the lower ruler, ensured that the rulers lay on the same straight line for the eye (if you look along the upper ruler). After this, he took the circle out of the water and compared the angles of incidence α and refraction β. It measured angles with an accuracy of 0.5°. The numbers obtained by Ptolemy are presented in the table.
Ptolemy did not find a “formula” for the relationship between these two series of numbers. However, if we determine the sines of these angles, it turns out that the ratio of the sines is expressed by almost the same number, even with such a rough measurement of angles, which Ptolemy resorted to.
Due to the refraction of light in a calm atmosphere, the apparent position of stars in the sky relative to the horizon
1) higher than actual position
2) below actual position
3) shifted to one side or another vertically relative to the actual position
4) matches the actual position
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In a calm atmosphere, the position of stars that are not perpendicular to the Earth’s surface at the point where the observer is located is observed. What is the apparent position of the stars - above or below their actual position relative to the horizon? Explain your answer.
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In the text, refraction refers to the phenomenon
1) changes in the direction of propagation of a light beam due to reflection at the boundary of the atmosphere
2) changes in the direction of propagation of a light beam due to refraction in the Earth's atmosphere
3) absorption of light as it propagates through the Earth's atmosphere
4) bending of a light beam around obstacles and thereby deviation from rectilinear propagation
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Which of the following conclusions contradicts Ptolemy's experiments?
1) the angle of refraction is less than the angle of incidence when the beam passes from air to water
2) As the angle of incidence increases, the angle of refraction increases linearly
3) the ratio of the sine of the angle of incidence to the sine of the angle of refraction does not change
4) the sine of the angle of refraction depends linearly on the sine of the angle of incidence
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Photoluminescence
Some substances themselves begin to glow when illuminated by electromagnetic radiation. This glow, or luminescence, has an important feature: the luminescent light has a different spectral composition than the light that caused the glow. Observations show that luminescence light has a longer wavelength than the exciting light. For example, if a beam of violet light is directed at a cone containing a fluorescein solution, the illuminated liquid begins to luminesce brightly with green-yellow light.
Some bodies retain the ability to glow for some time after their illumination has ceased. This afterglow can have different durations: from a fraction of a second to many hours. It is customary to call a glow that stops with illumination fluorescence, and a glow that has a noticeable duration is phosphorescence.
Phosphorescent crystalline powders are used to coat special screens that retain their glow for two to three minutes after illumination. Such screens also glow when exposed to X-rays.
Phosphorescent powders have found very important use in the manufacture of fluorescent lamps. In gas-discharge lamps filled with mercury vapor, ultraviolet radiation occurs when an electric current passes. Soviet physicist S.I. Vavilov proposed covering the inner surface of such lamps with a specially prepared phosphorescent composition, which produces visible light when irradiated with ultraviolet light. By selecting the composition of the phosphorescent substance, it is possible to obtain the spectral composition of the emitted light as close as possible to the spectral composition of daylight.
The phenomenon of luminescence is characterized by extremely high sensitivity: sometimes 10 – 10 g of a luminous substance, for example in a solution, is enough to detect this substance by its characteristic glow. This property is the basis of luminescent analysis, which makes it possible to detect negligible impurities and judge about contaminants or processes leading to changes in the original substance.
Human tissues contain a large number of diverse natural fluorophores, which have different fluorescence spectral regions. The figure shows the emission spectra of the main fluorophores of biological tissues and the scale of electromagnetic waves.
According to the data presented, pyroxidine glows
1) red light
2) yellow light
3) green light
4) purple light
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Two identical crystals, which have the property of phosphorescent in the yellow part of the spectrum, were preliminarily illuminated: the first with red rays, the second with blue rays. For which of the crystals can the afterglow be observed? Explain your answer.
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When examining food products, the luminescent method can be used to identify spoilage and falsification of products.
The table shows the luminescence indicators of fats.
The luminescence color of the butter changed from yellow-green to blue. This means that the butter may have been added
1) only creamy margarine
2) only “Extra” margarine
3) only vegetable lard
4) any of the following fats
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Albedo of the Earth
The temperature at the Earth's surface depends on the reflectivity of the planet - albedo. Surface albedo is the ratio of the energy flux of reflected solar rays to the energy flux of solar rays incident on the surface, expressed as a percentage or fraction of a unit. The Earth's albedo in the visible part of the spectrum is about 40%. In the absence of clouds it would be about 15%.
Albedo depends on many factors: the presence and condition of cloudiness, changes in glaciers, time of year, and, accordingly, precipitation.
In the 90s of the 20th century, the significant role of aerosols—“clouds” of tiny solid and liquid particles in the atmosphere—became obvious. When fuel is burned, gaseous sulfur and nitrogen oxides are released into the air; combining in the atmosphere with water droplets, they form sulfuric, nitric acids and ammonia, which then turn into sulfate and nitrate aerosols. Aerosols not only reflect sunlight, preventing it from reaching the Earth's surface. Aerosol particles serve as condensation nuclei for atmospheric moisture during cloud formation and thereby contribute to an increase in cloudiness. And this, in turn, reduces the flow of solar heat to the earth's surface.
Transparency to sunlight in the lower layers of the earth's atmosphere also depends on fires. Due to fires, dust and soot rise into the atmosphere, which cover the Earth with a dense screen and increase the albedo of the surface.
Which statements are true?
A. Aerosols reflect sunlight and thereby help reduce the Earth's albedo.
B. Volcanic eruptions increase the Earth's albedo.
1) only A
2) only B
3) both A and B
4) neither A nor B
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The table shows some characteristics for the planets of the solar system - Venus and Mars. It is known that the albedo of Venus A 1= 0.76, and the albedo of Mars A 2= 0.15. Which of the characteristics mainly influenced the difference in the albedo of the planets?
1) A 2) B 3) IN 4) G
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Does the Earth's albedo increase or decrease during volcanic eruptions? Explain your answer.
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Surface albedo refers to
1) total flux of solar rays incident on the Earth's surface
2) ratio of reflected radiation energy flux to absorbed radiation flux
3) ratio of reflected radiation energy flux to incident radiation flux
4) difference between incident and reflected radiation energy
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Study of spectra
All heated bodies emit electromagnetic waves. To experimentally study the dependence of radiation intensity on wavelength, it is necessary:
1) decompose the radiation into a spectrum;
2) measure the energy distribution in the spectrum.
Spectral devices - spectrographs - are used to obtain and study spectra. The diagram of the prism spectrograph is shown in the figure. The radiation under study first enters a tube, at one end of which there is a screen with a narrow slit, and at the other - a collecting lens L 1 . The slit is at the focal point of the lens. Therefore, a diverging light beam incident on the lens from the slit emerges from it as a parallel beam and falls on the prism R.
Since different frequencies correspond to different refractive indices, parallel beams of different colors come out of the prism, but do not coincide in direction. They fall on the lens L 2. At the focal length of this lens there is a screen, ground glass or photographic plate. Lens L 2 focuses parallel beams of rays on the screen, and instead of a single image of the slit, a whole series of images is obtained. Each frequency (more precisely, a narrow spectral interval) has its own image in the form of a colored stripe. All these images together
and form a spectrum.
Radiation energy causes the body to heat up, so it is enough to measure the body temperature and use it to judge the amount of energy absorbed per unit time. As a sensitive element, you can take a thin metal plate coated with a thin layer of soot, and by heating the plate, judge the radiation energy in a given part of the spectrum.
The decomposition of light into a spectrum in the apparatus shown in the figure is based on
1) phenomenon of light dispersion
2) phenomenon of light reflection
3) phenomenon of light absorption
4) properties of a thin lens
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In a prism spectrograph device, the lens L 2 (see figure) is used for
1) decomposition of light into spectrum
2) focusing rays of a certain frequency into a narrow strip on the screen
3) determination of radiation intensity in different parts of the spectrum
4) converting a diverging light beam into parallel rays
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Is it necessary to cover the metal plate of a thermometer used in a spectrograph with a layer of soot? Explain your answer.
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