The blogger took a fantastic photo, but it was not without Photoshop.
The Andromeda Nebula in our sky looks six times the size of the full moon. The user of Reddit (the most popular social network in the West) illustrated this paradox in a much more obvious way: he published a photo in which, in fact, everything is visible. The long axis of the nebula has an angular size of 3.2 degrees. And the angular diameter of the moon is only half a degree. The difference is obvious. Why can everyone find the moon, but not everyone has seen the Andromeda nebula?
The answer is obvious: the moon is bright and the Andromeda nebula is dim. In fact, it is quite visible even with binoculars, and people with good eyesight will notice it with simple eyes, but visually you see only the brightest part of the nebula, its core. To make it appear in all its glory, you need to take a photo with a very long exposure. The camera sensor (or film emulsion) accumulates photons and displays the true picture. True, this photo was not without Photoshop. If you “just shoot”, the moon will fill the whole picture with its light. Two photos are taken, a long one with a nebula, and a fast one with the Moon, then the photos are combined.
Celestial objects are usually deceiving, what is actually huge appears to us tiny and inconspicuous, and vice versa. But here everything is fair: the Andromeda nebula is actually larger than the Moon (there is nothing to compare), and looks bigger. Actually, the Andromeda nebula is the most distant object in the sky that a person can see with simple eyes. The light from it goes to us 2.5 million years (from the Moon - a second). The Andromeda Nebula is actually a grand galaxy like ours, it has about a trillion stars, and that's even much more than our galaxy. Why is it called "nebula"? Traditionally.
People noticed her in antiquity, but had no idea that she was like our Milky Way. They called it "little cloud". Telescopes, photography, sophisticated instruments appeared, and people still did not understand what the Andromeda nebula was. And in 1923, special stars were noticed in it, which are called Cepheids. These stars change their brilliance. The beauty of these stars is that the timing of the change in brightness is very closely related to the true luminosity of the star. You can tell how big a Cepheid is by simply measuring how many days and hours it takes to change its brightness. And, knowing how it looks from the Earth, you will immediately calculate the distance. They began to study the Cepheids of the Andromeda nebula, and on those, it turned out, this "nebula" is so far away, outside our Galaxy! So it was discovered that the universe consists of galaxies. Recently, a hundred years have not passed.
The Andromeda Nebula is flying towards us, and in four billion years will collide with our galaxy. "Small cloud" will eventually occupy our entire sky. What will happen? The question is a bit idle, because the Sun will be gone. However, we can see how the collision occurs in other galaxies - no good. Stars fly apart, black holes in the centers of galaxies explode. How the aliens feel with this - we do not know, so far nothing has sent an SOS signal from such galaxies.
EVGENY ARSYUKHIN