When in 1957 the USSR launched the world's first artificial satellite into Earth orbit,
there was a panic in the USA, because it was believed that the USSR was a technologically backward country.
What is space optics capable of? Is it true that from a satellite you can see car numbers, stars on shoulder straps and headlines in newspapers - as the townsfolk frightened each other in times Cold war? Cosmoblogger ZELENYIKOT on specific examples talks about the capabilities of modern satellites.
To begin with, a small discovery for many: in Google map no satellite imagery with a resolution higher than 50 cm per pixel. Until recently, commercial distribution of more detailed satellite imagery was prohibited in the United States. Therefore, if you find pictures in any city where people walking and other details are visible - this is an aerial photography, you can publish it.
Such a contradiction did not suit space privateers for a long time, and they nevertheless lobbied for a relaxation of the law, and now it is possible to sell images with a resolution of up to 25 cm per pixel. Today, this is the limit of commercial satellite imagery.
But even such shots require the most sophisticated technique. For example, DigitalGlobe's WorldView-3 satellite has a resolution of 31 cm, a telescope mirror diameter of 1.1 m, and a cost of $ 650 million.
For example, DigitalGlobe posted pictures of Madrid.
As you can see, you can consider many details: Cars easy to distinguish from cargo, even, it seems, people swimming in pools can be seen in the form of dots. But Madrid was not chosen by chance: the closer to the equator, the less cloudiness. Also, to demonstrate the capabilities of satellites, Dubai is often chosen - there are many all sorts of colorful objects, and the desert weather facilitates observation.
The colossal costs of creating private satellites capable of such quality of imaging raise a natural question: how do they pay off? This is no secret: more than 50% of DigitalGlobe's orders come from the Pentagon. The rest is from Google and individual customers.
But these are still commercial satellites, so what can the military and the CIA do?
Everything is more complicated here, but on the whole it is quite predictable. The legendary and most powerful American spy satellite belongs to the Keyhole-11 series. Reliably little is known about it, even the appearance is not fully clarified, although amateur astronomers periodically "intercept" it.
But it is known that the Hubble space telescope was created on a production line from which spy satellites previously descended, and a couple of years ago, the American spy department (National Reconnaissance Office) donated two telescopes with a diameter of 2.4 meters to NASA, which were lying around in a warehouse.
Therefore, most likely, KH-11 has a mirror with a diameter of 2.4 meters, like the famous Hubble space telescope.
By simple comparison with WorldView-3, which has a 1.1 meter mirror, we find that the quality of spy shots should be about 2.3 times better. But there is a difference: WorldView-3 flies at an altitude of 617 km, and the youngest KH-11 (called USA-245) at an altitude of 270 to 970 km.
The Hubble Space Telescope from an altitude of 700 km could photograph the Earth with a resolution of up to 10-15 cm, in ideal conditions, if it were allowed technical capabilities... Accordingly, the KH-11 at the lowest point of its orbit is capable of giving a resolution of up to 5 cm. But, again, this is in ideal conditions, in the absence of clouds, smog, fog and just dust over the subject. In addition, the higher the resolution, and the closer the satellite is to the Earth's surface, the narrower its capture bandwidth and the less opportunity to look around. That is, it is advisable to use such a survey only for previously explored objects, in clear weather, and only during the time that is due to the orbit of the vehicle.
Because the American military and the American commerce technical means not enough, and it's easier to buy the images you want than to create a bunch of satellites, each costing the size of an aircraft carrier.
And to present the quality of the images in different resolution, I prepared an example scheme based on aerial photography data.
Thus, in ideal conditions, in theory, just one spy satellite is able to see the license plate bar on a car as a few white pixels. But to read the issue, not to mention the shoulder straps and newspapers, is simply physically impossible.
Many believe that the International Space Station (ISS) flies somewhere very far, and in order to see it (and even more so to photograph it) you need special equipment... However, this is not at all the case. The ISS flies over our heads several times every day and it is no more difficult to see it than an ordinary passenger plane. You just need to know when and where to look. In terms of brightness, the ISS can even compete with Jupiter and Venus, and its rapid movement across the sky attracts even more attention. In this article I want to tell you how and when you can see the ISS tonight in Moscow, I will tell you how to find out the time of flight of the ISS for any other place and date, as well as touch on the topic of photo and video filming of the ISS.
What is required for observations?
Telescopes and binoculars will not help us, even more likely to harm. The fact is that the ISS is moving very quickly, catch and track it optical instrument With high magnification hard. This GIF gives some idea of its speed.
And we need a clear sky (tonight this is all right):
… and open area With good overview to the southwest, south and southeast (for example, supermarket parking, sports ground, building roof, etc.). The proximity of bright lanterns will not hurt us, since the ISS is a very bright object. If you are too lazy to go outside, you can get by with a balcony or window facing south.
You also need a clock synchronized with exact time, and a compass (in case you do not know at least the approximate directions to the cardinal points at the selected point for observation).
When and where to look?
The ISS makes one orbit in about an hour and a half. This means that if the Earth did not rotate, we would see the ISS passing along the same trajectory every hour and a half. Since the Earth still rotates, the "track" from the ISS on the Earth's surface is shifted to the west with each revolution. In addition, the ISS is visible only when it is itself illuminated by the Sun, while it has already become dark at the observer's location (you can contrive, but this is more difficult). To calculate the current visible passages of the ISS over Moscow, I used the heavens-above.com online service (residents of other cities can easily get visibility conditions of the ISS there on their own). The most favorable flight for observation is expected. today at about 22:47.
The stars on the map will not help us much, since they are not very visible in the city. It's easier to navigate to the cardinal points using a compass. If there is no compass, look for the direction where the evening dawn dies down, there will be northwest.
ISS will ascend in 22:42:30 , but it is too early to start looking for it at this time. Near the horizon, it is not yet bright enough, besides, trees, buildings and haze can interfere with the view. Better to wait until it rises at least 10 degrees above the horizon. This will happen in 22:44:38 , The ISS will be somewhere between west and southwest. You will notice a dim, unblinking star moving slowly to the left and up. This star is the ISS flying somewhere over France at a distance of one and a half thousand kilometers. Do not rush to get upset if you did not manage to notice it at that moment - you could have been hindered by light clouds near the horizon or you yourself were a little misled with the direction. The asterisk will move faster and faster, flare up more and more, and in a minute it will be much easier to find it. The station will reach a maximum altitude of 40 degrees in 22:47:43 being practically in the south in azimuth. At this moment, the ISS will be just below the star Altair, in terms of brightness it will be comparable to Venus, and in terms of angular velocity - with a jet plane. The distance to it will be about 600 km. Then the ISS will descend, moving to the east, and in 22:48:52 will enter the shadow of the Earth. Due to the presence of the atmosphere, the brightness of the station will not drop instantly. It will fade out smoothly for ten seconds. Particularly attentive observers will notice that the ISS will turn red before extinguishing. Indeed, at this moment the astronauts on board will see the sunset, and at sunset the sun's rays turn red. When the station is finally out of sight, look east and, as a bonus, you will see the moon rising.
Note: The times indicated above will be correct with a second precision for an observer on Red Square. If you are far from the center, there will be a few seconds difference. For example, in Reutov maximum height will be reached 2 seconds later. Entering the shadow, of course, will occur simultaneously for all observers.
Another flight less convenient for observations will occur in a loop earlier, in 21:11 ... You can try to observe it first, but at 9 pm it is still quite light and the ISS will be difficult to notice against the background of a bright sky. In addition, the station will rise by only 28 degrees.
How to take a photo of the ISS or film it?
If you are going to observe the ISS for the first time, then I recommend not to be distracted by the photo for now. Better look with your eyes, get an idea of the brightness and speed. Next time, for example tomorrow, you can already go out with a camera. Set a long exposure of 10-30 seconds. Adjust the aperture and sensitivity so as not to overexpose the sky, but at the same time to see the stars. Mount the camera on a tripod and point it towards the area of the sky where the flight is expected. A few minutes earlier, you can take a test shot in order to be guided by the stars to make sure that the desired area of the sky falls into the frame. As a result, you can get a frame like this (the photo is not mine, I found it on Google Images).
If a flight is expected near the moon, then you can catch an interesting shot. For example, I got this:
In the dynamics it looked like this (filmed with a compact Panasonic HDC-SD90 camcorder).
What about the Moon and Sun transits shown at the beginning of the article?
Recently news portals the news spread that NASA published unique images of the ISS against the background of the moon. Even on Giktimes about it. In fact, there is nothing unusual in that photo, you can make sure of this by searching for keywords "iss transit"in Google Images. I was able to take a similar photo and video on my first attempt with rather modest equipment (the same as I used in the article):
It is better to watch the video in full screen mode:
The main problem here is that the shadow (or rather penumbra) thrown by the ISS from the Sun or the Moon has dimensions of only a few kilometers. In an arbitrary place, such a phenomenon happens extremely rarely, so you have to wait for the right moment, get into the car and drive several tens of kilometers. To find out when and where to go, you can use the calsky.com service. There you can get a map showing where the shadow of the ISS will run in the next couple of days. For example, here is a fragment of the map of the nearest transit on the Moon.
Conclusion
Hopefully, thanks to this article, many readers will go outside tonight and look up at the sky. I suggest you share your impressions in the comments!
It is easier to see the sun during the day, but you should not look at it directly - you can seriously damage your eyes. During eclipses, the danger increases many times over. However, it is also easy to protect yourself from this - with special light filters or by observing the projection.
The moon is also by no means a rare guest in the daytime sky, it appears from different frequency and brightness depending on its own phases. The easiest way to find it is on the new moon.
Venus, also called the "morning star" and "evening star", reflects the light of the Sun so well that it is relatively easy to see it during the day, especially if you know its location. It appears as a tiny blinking white point.
Satellites. At night, satellites look like "moving stars" and require attention and patience to see them. But during the day, you can also see at least one kind of satellites - "Iridium". Their antennas periodically reflect light so brightly that this effect is called the "Iridium flash" and is visible even in the daytime sky.
Jupiter in the daytime sky is extremely difficult to see. Sharp eyesight and excellent atmospheric conditions are required. The best time for observation - when Jupiter is at 90 degrees from the Sun during the first and last quarter of the Moon.
Mars. If Jupiter is difficult to see during the day, Mars is almost impossible. But precisely that "almost" - under rare conditions, similar to those when observing Jupiter, the red planet can be seen in the daytime sky.
The stars can actually be seen during the day during a solar eclipse, although this is a dishonest move. Nevertheless, such observations were of great historical importance, at one time confirming Einstein's theory of relativity. With perfect vision and incredible luck, you can see the most bright stars like Sirius in the daytime sky, but it's better to use a telescope anyway.
Comets flying near the Earth are easy to see in the daytime - the main thing is to wait the right moment... For example, Comet McNaught in 2007 was clearly visible during the day, as was Comet Halley in 1910.
Meteors are rare and unpredictable, but the brightest of them are clearly visible in the daytime sky. They are even filmed, as was the case in one of the most famous sightings in the United States in 1972.
Supernova explosions can be seen from Earth with the naked eye at irregular intervals from 20 to 300 years. The last evidence that a similar phenomenon was observed during the day dates back to 1572. The first candidate for a new explosion is the star Betelgeuse. Of course, its supernova will be visible during the day, but it is not known whether the explosion will occur tomorrow or thousands of years later.
Of course, the Sun is at the top of this list - as the most obvious candidate, but the rest of the objects may surprise. For some, you will have to properly strain your eyes or use binoculars, for others - wait for the right moment. What kind of bodies from space are visible on Earth during the day?
As part of the review of the features of observation of artificial Earth satellites, in the previous article we stopped at the review of the advanced artificial Earth satellite - the ISS; in the previous article, we stopped at the review of the advanced artificial Earth satellite - the ISS - the International Space Station, we learned how to observe the flight of the ISS.
The main thing that is needed to observe artificial satellites is good vision and a forecast indicating their passage over various points of the planet. Of course, with binoculars or a telescope, you can see details and objects that are inaccessible to the naked eye. With 7x50 binoculars (that is, binoculars with 50 mm objectives that provide 7x magnification), you can already observe objects of magnitude 8 to 9 in a stationary atmosphere in a very dark sky.
For owners of a 114 mm telescope, even artificial satellites 10-11 magnitude, that is, much lower brightness. With some experience, you can learn to "track" a satellite manually, but things get easier with a clock motor connected to a computer where the coordinates of the satellite are entered. There are excellent programs on the market in which you can find data on hundreds of artificial satellites in low orbit; Thanks to these programs, the telescope's clock motor follows them easily automatically.
How many artificial satellites are available for observation?
Regardless of the place of observation, at any hour of the day, hundreds of artificial satellites are located above the horizon. However, only a few dozen are readily available for observation at favorable conditions lighting.
The Russian Soyuz spacecraft (or their cargo version Progress) are also among the man-made objects potentially available for observation from Earth. "Soyuz" and "Progress" under favorable lighting conditions reach magnitude 1, and under normal conditions they exceed magnitude 3. Thus, they can be seen with the naked eye, however, only as luminous points. To get some details, you can first check the Soyuz visibility conditions in the days immediately after launch, and then use your telescope.
Typically, one or two objects can be seen with the naked eye every half hour; when using a telescope like yours, their number increases to 10. The brightest artificial satellites are listed on the website n2yo.com/satellites/7cH... This site contains mainly technical information on the English language, but with some experience you will be able to mine the most important information and navigate among the data relating to different satellites.
About photogenicity. Like other celestial objects, artificial satellites can be photographed through a telescope. Some astronomy lovers, for example, have excellent photographs of the Mir station, taken before its death in the atmosphere, and the International Space Station. In these pictures, you can even see the various laboratories of the stations.
And there is "rubbish" too. With the help of a telescope, you can see over 10,000 objects of space debris flying in near-earth orbit. Typically, these are parts of the rockets used to launch a satellite or space station that remain in orbit after use. There are also fragments of exploded missiles or decommissioned satellites. Calculating the orbits of these objects and their location is very difficult. Nevertheless, the largest space agencies have this information and use it in order to avoid collisions with active satellites or the International Space Station.
What and how can you see in search of satellites?
Usually an artificial satellite looks like a slowly moving star in the sky. There are many exceptions to this rule, however. Some artificial satellites, for example, change their brightness just at the moment they pass over the observation point. This is usually caused by changing lighting conditions, sometimes producing very spectacular effects. Again, everything depends on the satellite's height above the Earth, on its size and on the characteristics of its surface (in particular, reflectivity).
Distance. The brightest satellites visible to the naked eye are most often the fastest moving satellites, since they are in low orbits and, therefore, are located closer to the observer. For monitoring much more distant geostationary satellites on the contrary, a telescope is almost always necessary. During the passage through the sky, most of the satellites change their brightness by more than one stellar magnitude (with the exception of the Iridium satellites, but some of them can disappear completely, falling into the cone of the earth's shadow, and then reappear. The distance from the satellite to the observer is called "Range" and is measured in kilometers or miles. Typically, the higher the range value, the fainter the satellite is visible. Range depends on the height of the orbit above the Earth, as well as its inclination to the Earth's horizon. A satellite with a very high orbit passing through the zenith (then overhead) may have a range less than a satellite in a lower but more inclined orbit, which brought it to a position low above the horizon.In this case, a satellite in a higher orbit will be brighter than a satellite. located at a lower height.
The determining factor for the brightness of a satellite is its size. The larger the satellite, the brighter it shines, since the larger the surface is capable of reflecting sunlight. This surface is denoted by the term "Radar Cross Section".
Surface characteristics. Artificial with a traveler with a highly reflective surface will obviously appear brighter. Over time, its surface will become cloudy, and this satellite will change its brightness value, perhaps even by one stellar magnitude. Conversely, a low-reflective surface, when destroyed, can become brighter and reflect light better. Others important parameter is the presence of some functional parts of the satellite, such as solar panels or cylindrical antennas, often acting as mirrors. These add-ons can cause a "flash" effect lasting several seconds (sometimes predictable in advance), sharply increasing the brightness of an object by several magnitudes.
The last factor that must be borne in mind when determining the brightness of an artificial satellite is the angle of incidence of the sun's rays. As with the Moon, they can illuminate an object more or less directly and fully.
Flash in space. In 1997, the first satellites of the Iridium series designed for a new type cellular... It was originally planned that there will be 77 of them, this explains the name Iridium (a chemical element with an atomic number of 77). But as a result, 95 were launched, of which 72 are still in operation. Satellites placed in polar orbits were supposed to guarantee communication from any point the globe from anywhere in the world. Today there are tens of thousands of subscribers to this network, but this service has not achieved the planned success.
Super-aerials. The dimensions of the satellites of the Iridium series are relatively small. They reach 4 m in length and, in addition to solar panels, have three main antennas, 188 cm long and 86 cm wide. These antennas have excellent reflectivity. It is they who give the Iridium satellites a unique characteristic, which makes it possible to single out these satellites in a special category, attracting thousands of fans astronomical observations... The fact is that they appear in the sky at a relatively low brightness, but, unlike other satellites, within a few seconds they can become 50 or more times brighter than Venus for a short time. Then their brightness decreases to normal at the same rate with which they were previously so bright.
Iridiums are the only ones artificial satellites that can be observed during the day. It is not very easy, but if the sky is clear of clouds and is colored bright blue, flashes of at least -6 magnitude can sometimes be seen. To find them in the daytime sky, you need to know exactly the points at which these flashes should appear.
Heavenly sparkle. The characteristic sparkling of the Iridium is easily explained: to fulfill the set technical challenge these satellites are positioned in space in such a way that most often one of the antennas reflects the sun's rays directly to the Earth, and this causes a bright flash.
Such flares can be calculated in advance with absolute accuracy, and therefore they are not difficult to observe from Earth. It is only important to know exact coordinates observation points: a difference of a few kilometers is enough for the brightness to change by several magnitudes. The brightest flares reach values up to -8 and are available for observation from an area of several square kilometers. The transition from brightness +6 (at the limit of visibility to the naked eye) to -8 means that the object increases its brightness 400,000 times.
© Collect your telescope # 20, 2015
Now the topic of satellite images is often raised in conversations far from space. At the same time, ancient myths of the Cold War, about "reading the license plate" and "counting the stars on the shoulder straps" or even "reading the newspaper", are washed from discussion to discussion.
Today, with specific examples, we will look at what space optics is capable of, and whether everything is visible from above.
For starters, a small revelation for many: Google Map does not have satellite images with a resolution higher than 50 cm per pixel. Until recently, commercial distribution of more detailed satellite imagery was prohibited in the United States. Therefore, if you find pictures in any city where people walking and other details are visible - this is an aerial photography, you can publish it.
Such a contradiction did not suit space privateers for a long time, and they nevertheless lobbied for a relaxation of the law, and now it is possible to sell images with a resolution of up to 25 cm per pixel. Today, this is the limit of commercial satellite imagery.
But even such shots require the most sophisticated technique. For example, DigitalGlobe's WorldView-3 satellite has a resolution of 31 cm, a telescope mirror diameter of 1.1 m, and a cost of $ 650 million.
For example, DigitalGlobe posted pictures of Madrid.
As you can see, many details can be considered: passenger cars can be easily distinguished from trucks, even, it seems, people swimming in pools can be viewed as dots. But Madrid was not chosen by chance: the closer to the equator, the less cloudiness. Also, to demonstrate the capabilities of satellites, Dubai is often chosen - there are many all sorts of colorful objects, and the desert weather facilitates observation.
The colossal costs of creating private satellites capable of such quality of imaging raise a natural question: how do they pay off? This is no secret: more than 50% of DigitalGlobe's orders come from the Pentagon. The rest is from Google and individual customers.
But these are still commercial satellites, so what can the military and the CIA do?
Everything is more complicated here, but on the whole it is quite predictable. The legendary and most powerful American spy satellite belongs to the Keyhole-11 series. Reliably little is known about it, even the appearance is not fully clarified, although amateur astronomers periodically "intercept" it.
But it is known that the Hubble space telescope was created on a production line from which spy satellites previously descended, and a couple of years ago, the American spy department (National Reconnaissance Office) donated two telescopes with a diameter of 2.4 meters to NASA, which were lying around in a warehouse.
Therefore, most likely, KH-11 has a mirror with a diameter of 2.4 meters, like the famous Hubble space telescope.
By simple comparison with WorldView-3, which has a 1.1 meter mirror, we find that the quality of spy shots should be about 2.3 times better. But there is a difference: WorldView-3 flies at an altitude of 617 km, and the youngest KH-11 (called USA-245) at an altitude of 270 to 970 km.
The Hubble Space Telescope from an altitude of 700 km could photograph the Earth with a resolution of up to 10-15 cm, in ideal conditions, if technical capabilities allowed it. Accordingly, the KH-11 at the lowest point of its orbit is capable of giving a resolution of up to 5 cm. But, again, this is in ideal conditions, in the absence of clouds, smog, fog and just dust over the subject. In addition, the higher the resolution and the closer the satellite is to the Earth's surface, the at the same swath of his shooting and less opportunity to look around. Those. it is advisable to use such a survey only for previously explored objects, in clear weather, and only at a time that is determined by the orbit of the vehicle.
Because the American military pays the American commerce, that their technical means are not enough, and it is easier to buy the necessary images than to create a bunch of satellites, each costing the same as an aircraft carrier.
And in order to represent the quality of images in different resolutions, I have prepared an approximate diagram based on aerial photography data.
Thus, in ideal conditions, theoretically, only one spy satellite is able to see the license plate bar on a car in the form of several white pixels. But to read the issue, not to mention the shoulder straps and newspapers, is simply physically impossible.
