“P” out of the starry sky

Astronomical telescopes are the main tools for observing celestial bodies and capturing information about celestial bodies. Since Galileo made the first telescope in 1609, the telescope has been developing continuously. From the optical band to the full band, from the ground to the space, the telescope’s observation ability has become stronger and stronger, and more and more celestial body information can be captured. Human expectations More discoveries with astronomical telescopes.

  On July 12, 2022, NASA officially released a batch of full-color images of the universe taken by the James Webb Space Telescope on its official website. They are the first images released more than half a year after the Webb Space Telescope took off. The first five sets of space pictures released by the “successor” of the Hubble Space Telescope are clear, detailed and extremely shocking. No wonder some people say: This $10 billion space telescope is worth the money! Previously, Webb Space Telescope predecessors “Hubble” and “Spitzer” have shown us extremely beautiful space photos, whether it is the Large Magellanic Cloud like an exploding fireball, or the Helix Nebula like a huge green eye; Whether it is the Orion Nebula that blooms like fire or the Carina Nebula that blooms like a rose, many people are interested in astronomy because of these magnificent pictures of the starry sky.
  But in fact, these pictures are all made by computers. In the current Internet language, these astronomical photos are all “p”. Of course, making these astronomical pictures is not a fake, nor is it simply a matter of applying a few filters to the PS software. Making these astronomical pictures requires a lot of observational data, professional astronomical knowledge and superb artistic attainments. So, what did these beautiful starry sky pictures originally look like? And what made it look what we see?
hard-earned cosmic photos

  Taking pictures with a space telescope is not like taking a picture with a camera, aiming at the thing to be photographed, adjusting the focal length and pressing the shutter. For space telescopes, it is already a big problem to be able to photograph the target. After all, the universe is too big, and many of the targets are a few light-years or even thousands of light-years away from us, and many of the targets are the size of the entire Milky Way, and the space telescope is constantly moving… So, Most of the shooting of space telescopes is to take hundreds or even thousands of photos in the same area, and then compare and stitch them together to “patch” the celestial objects that you want to shoot. This is only the first step. Next, it is necessary to “grind” the astronomical pictures. It is said to be “dermabrasion”, but it is actually to remove the interference information and invalid information in the photo. If you take a picture of the night sky with an ordinary camera, you will know that when the sensitivity is increased at night, there will be a lot of noise, making it difficult to distinguish which stars are. , Which are the satellites and which are the noise of the camera. To get a clear night sky photo, you need to take a few more photos at the same angle, and then use the photo editing software to superimpose these photos to determine which are stars and which are interference, remove them After the interference, a relatively pure starry sky photo can be obtained.
  For space telescopes, the technology of image stacking is much more complicated than what we take with ordinary cameras. For example, the Hubble telescope takes an extremely dim celestial object, except for a few Milky Way stars in the foreground, more than 3,000 can be seen. The celestial bodies are almost all distant galaxies, reaching tens of billions of light-years away. Such a distant and dim starlight forced the Hubble telescope to circle the earth 150 times in 10 days, accumulating 141 hours of exposure to the same sky area. In the end, 342 photos were selected to be superimposed to remove the interference of cosmic rays and scattered light from the earth, and to enhance the real signal, in order to synthesize a real astronomical photo. Don’t worry, if you see this photo at this time, you must not know what the photo was taken, because what you see at this time is just a black and white photo full of blurred spots. That’s right, the photos taken by the space telescope are all black and white, and the astronomical photos we see are all colorized later.
  Why do you still need to take black and white photos when the technology is so advanced? In fact, this is not to blame for the space telescope, but to blame people’s eyes “too unsatisfactory”. Electromagnetic waves in the universe are very broad, and only a very narrow band of them can be perceived by human eyes. This part is called visible light. But if we use visible light to observe space, then what we can see is only a drop in the universe. Scientists get the initial photos, marked with black and white photos such as x-ray band, infrared band, microwave band, let alone ordinary people, even experts can only imagine what it looks like by looking at these photos through data, after all, scientists’ eyes are also Just like normal people, so the next step is to colorize these black and white photos.
  Coloring astronomical photos is a massive project that combines authenticity, science, and artistry. Take the classic astrophotography work “Pillars of Creation” as an example. The “Pillars of Creation” is located in the Eagle Nebula, about 7,000 light-years away from Earth. In the photo, a huge “pillar” runs vertically through the entire starry sky. On the upper part of the “pillar”, three stalagmite-like spires emerge from the green haze, just like the towers in the castles in fairy tales. The top ejects a blue band of light. Bright stars shine through the gaseous gaps, and the outlines of these stars are like bright yellow borders used to decorate objects, which are particularly dazzling. It is difficult for people to imagine how huge these “pillars” are in reality. Each “pillar” is several light years long, which means that even light takes years to travel from the bottom of the “pillar” to the top. . Through the data, scientists speculate that the three “pillars” are a mixture of interstellar hydrogen and dust. The surface and interior of the “pillars” contain evaporative gas spheres, which means that new stars will be born in these “pillars” continuously , is like a huge stellar “nursery”, so it is named “Pillars of Creation”.
  The “Pillars of Creation” is considered to be one of the most successful pictures taken by the Hubble Space Telescope, and this magnificent and beautiful picture has been widely printed on various household items. However, if one day people can make interstellar travel, even if they fly to the most suitable observation site, people will not be able to see this beautiful “pillar of creation”, because under the observation of human eyes, the “pillar of creation” is only A cloud of red, fuzzy dust. This is because only a small part of the “Pillar of Creation” is in the visible light range, so people can never appreciate its beauty with the naked eye alone, but in the lens of a wider-band space telescope, the “Pillar of Creation” can be displayed. original appearance.

  The original image of the “Pillars of Creation” is a black-and-white photo of 3 bands, 502nm blue-green glow of oxygen, 657nm red glow of hydrogen and nitrogen, and 673nm deep red glow of sulfur. These 3 photos are superimposed. Together, we get a picture of blood red and black, which is the closest to its real appearance under electromagnetic waves, but such a picture is completely meaningless, because this appearance is neither what people can see, in science There is no amount of information on the level either. Therefore, scientists also need to make these information into their best appearance, so they get the “pillar of creation” we see today, not only the color of the picture is more gorgeous, but also more beautiful and spectacular, and it is more convenient The scientific information of the constituent elements is conveyed.
The Milky Way “You Thought”

  Some people think that although the pictures of distant galaxies can only be made by scientists’ guesses, the Milky Way we are in can be seen by looking up. The pictures of the Milky Way that people see are always real, right? In fact, all the pictures of the Milky Way we have seen are also conjectured by scientists. At present, there is only one panoramic photo of the Milky Way part, which was synthesized by the Spitzer Telescope in 10 years and took 2 million photos, and this 20 billion pixel photo, if printed out, is enough to have a stadium So big. However, this photo is only composed of some blurred light spots, which is far from the photos of the Milky Way we usually see. If we do not explain in advance, people may not be able to see that this is our Milky Way.

The Milky Way refers to a bright, milky band across the starry sky. These stellar views are a feast for the eyes and mind, but taking a photo of the Milky Way is not easy.

  Why is it so hard to take a photo of the Milky Way? Can’t you just look up and see? In fact, what we see is only one side of the Milky Way. After hundreds of years of observations and calculations by countless scientists, we now know that the Milky Way is a spiral-shaped dish-shaped celestial body, while our solar system is on a cantilever on the opposite edge of the Milky Way. Just like we are in a room of a huge skyscraper, we can only see one side of the building as far as we can by sticking our head out the window, we have no idea what the whole building looks like. So, how big is the “skyscraper” of the Milky Way? If the solar system is a soccer ball and the nearest star to us is another soccer ball, then the two soccer balls are miles apart, and the Milky Way is made up of more than 200 billion soccer balls. If we want to take pictures of the entire Milky Way, even if we can reach the speed of light, it will take tens of thousands or even hundreds of thousands of years to find the right angle.
  In order to paint a panorama of the Milky Way, people have used satellites to measure the positions of about 1.14 billion stars. Because of the earth’s revolution, satellites take 360-degree views. Scientists make inferences about the size of these stars based on information such as their brightness and band data, thus creating the most detailed 3D model of the Milky Way ever built, of course, only a partial model. And according to this model, scientists began to speculate what other parts of the Milky Way looked like. For example, the structure of the Milky Way means that there may be a very massive black hole in the middle, and the gravity of this black hole makes the center of the Milky Way have more stars or Star clusters, so people use the number of star clusters to infer where the center of the Milky Way is, and so on.
  Of course, the real situation is much more complicated than this, because there are various interference factors in the Milky Way, a large number of crowded stars, dust and gas. After the electromagnetic waves emitted by these celestial bodies are partially absorbed and scattered by the gas and dust, the Interstellar matting effect that reduces luminosity. Scientists have to remove these obstacles one by one through various means. In the end, it is possible to infer what the entire Milky Way should look like based on what is known, and finally to become the Milky Way we see in the photos now. It’s really not easy! Therefore, if you see a beautiful space picture in the future, you must silently thank countless scientists for their hard work, because before you can appreciate this beautiful and gorgeous space picture, it must have gone through countless “makeup and hair styling”.