How many stars are there in the sky

Once Khoja Nasreddin was asked how many stars there are in the sky. He replied: This question has been of interest to me for a long time. But I think that it can only be solved by going up to the sky and counting the stars ...

The sage was right, albeit partially. Modern satellites and telescopes discover more and more distant galaxies, full of new and countless stars, and it seems that there will be no end to this ... But despite this, the answer to the question: How many stars are there in the sky? is not easy to give even to specialists.

Indeed, stars are not distributed throughout the Universe by a uniform "suspension", they are collected in vast groups - galaxies. For example, our Sun is located in the Milky Way galaxy, and only there are about 100 billion stars in it. But there are trillions of galaxies alone in the universe!

The ancient sage said that trying to count the stars is tantamount to counting all the grains of sand on all the shores on the whole earth. But if we do not need an exact number, but a rough estimate is enough, then we can take satellite images, establish an approximate total area of ​​a suitable coastline, find out the average thickness of the sand layer and, knowing the volume of all sand on Earth, divide it by the average volume of a grain of sand. It is not easy to get a rough figure, but it is possible.

If we return to heaven, then galaxies can act as such "beaches" for us: it is approximately established that in our galaxy 1011-1012

stars, and in the Universe there are 1011-1012 galaxies. A simple calculation shows that there should be 1022-1024 stars in the universe.

This is, of course, a rough figure, suggesting that our galaxy is quite average, that there are few deviations from the average, and that we have correctly estimated the number of galaxies in the universe. And the latter may turn out to be a very deceptive value, because for a long time it was believed that there are about 50 billion galaxies, and only the work of the Hubble orbiting telescope increased this figure by 2.5 times!

And even Hubble does not see everything. Apart from particularly distant or faint galaxies, many of them are simply invisible to a telescope operating in the optical range: they are obscured by a dense cloud of gas and dust that accompanies the process of active star formation. The Herschel infrared probe, which is preparing for launch this spring, will allow you to look into these distances (we talked about how it will work in the article "Glazasty").

It should be borne in mind that no one has ever actually undertaken to count the number of stars in a galaxy: usually some generalizing characteristic is measured, in particular, the luminosity of the galaxy. Then we can, roughly speaking, divide the luminosity of a galaxy by the average luminosity of a star at the same distance - and estimate the number of stars in it. This is how Herschel will work, "counting" galaxies and measuring their luminosity in the infrared range.

So you just have to wait - until you can say that the stars are not less than the above magnitude: 1, 000, 000, 000, 000, 000, 000, 000, 000, that is, a trillion trillion.