How Many Stars Are There?

On a clear night how many stars can be seen in the night sky? Well, that will depend on a number of different things. Are you in the Northern or Southern Hemisphere? How clear is the night sky, is the atmosphere crystal clear? Is there any light pollution from nearby city lights, and if so how much? At what altitude are you viewing the night sky, at a lower altitude near sea level or over 5000 feet above sea level? What is the temperature of the atmosphere, are you viewing the stars in the summer or winter? We will look at these questions and try to answer them as best we can.

First, on a given night there will probably be a small difference depending on whether you are in the Northern or Southern Hemisphere, but since the Earth revolves around the Sun changing its position in space relative to the galactic star field, along with the tilting of the Earths axis, these differences will tend to cancel out. So we will assume that one will see roughly an equal number of stars in the night sky in the Northern and Southern Hemispheres.

How clear is the night sky? Of course the clearer the sky the more stars that will be visible; we will make the assumption here that the sky is crystal clear, as clear as possible. Any degradation in the atmosphere will lower the number of stars that are visible. Going right along with this we will make the assumption that there is no light pollution, for the same reason.

What about the altitude that one is viewing the night sky from? Most people probably live at an altitude no higher than about 1000 feet, or thereabouts. Of course for the lucky people living at higher altitudes, such as the Denver area, more stars will be visible through a marginally thinner atmosphere.

Although the difference may only be slight, I think that there could be a marginally greater number of stars visible on a cold winter night with a calmer and more stable atmosphere overhead.

So now making these assumptions, how many stars can you expect to see on a given night? This will also vary according to the vision of any given person, but for most people about 2000 stars, more or less, can be easily seen on a given night. Since a magnitude of about 6.5 is considered to be the faintest star visible to the unaided eye, given this criteria there will probably be an upper limit of around 4500 stars that could possibly be visible in the night sky – either the Northern or Southern Hemisphere.

One final comment here which is, of course, rather obvious. This discussion has been about the number of stars visible with the unaided eye, with any optical aid the number of stars visible will increase – drastically so with more powerful telescopes.

The Milky Way Galaxy, its stellar disk about 100000 light-years across, is estimated to have a range of around 100 to 400 billion stars. This number has a high level of uncertainty for the simple reason that we are trying to estimate the number of stars from within the galaxy. That is since we live within the Milky Way Galaxy itself it is not really possible to accurately count the number of stars with our current technology. Perhaps we could get a more accurate assessment if we could view the galaxy from a distance outside of it, but that is not the case, so this range is our best estimate at the current time.

The Large Magellanic Cloud is the largest satellite galaxy of the Milky Way at a distance of about 163000 light-years, visible mainly in the Southern Hemisphere, or very close to the equator in the Northern Hemisphere, and is estimated to have about 30 billion stars. The Large Magellanic Cloud is about 14000 light-years across.

The Small Magellanic Cloud is orbiting the Milky Way Galaxy at a distance of about 200000 light-years and is about 7000 light-years across. It is estimated that the Small Magellanic Cloud contains approximately several hundred million stars, although I think this estimate is rather low. With a mass of about 7 billion times that of our Sun, I think the Small Magellanic Cloud could contain over a billion stars, although this is only a guess, and by no means certain.

The Universe is gigantic and of course, has an incredibly large number of stars. Our estimate of stars in the Universe will really be more of a guess, but it’s the best that we can do at the current time. There are two parts of the Universe – the observable Universe and the unobservable Universe. We will take a look at each of these in the following sections.

The observable Universe is, as the name implies, the part of the Universe which we can see. The limit of the observable Universe appears to be about 13.8 billion light-years, the time which has elapsed since the beginning of the Universe, the Big Bang, being about 13.8 billion years.

The most recent estimates of the number of galaxies in the observable Universe is around 2 trillion, and of course, this number could go up in the future. But if we use this figure of 2 trillion galaxies and make a very conservative estimate that the average galaxy would have around 100 billion stars, some galaxies being smaller and some much larger, then we come to a very rough estimate of about 200 billion trillion stars, or about 200 sextillion stars. Again, there is a very good chance this number could change in the future as our knowledge increases.

The unobservable Universe is the unseen and much larger portion of the Universe – unseen because distant galaxies are moving away from us at a speed greater than that of light, and so light from these far off galaxies can never reach us. It is important to note here that this does not violate the Special Theory Of Relativity since it is the empty intergalactic void of space which is expanding faster than the speed of light, probably due to the influence of the mysterious dark energy. Special Relativity Theory is concerned only with mass(positive) approaching the speed of light.

Although any estimate of the number of stars in the unobservable Universe is practically meaningless, for the sake of completeness this part of the Universe needs to be mentioned. It is after all by far the largest part of the Universe, current estimates(or guesses) are that it is over 1000 times larger than the observable Universe. So if we multiply our previous estimate for the observable Universe by 1000 we come to a figure of 200000 billion trillion stars, or about 200 septillion stars. Again, although this is only a wild guess, we had to give it a try and perhaps in the more distant future, our estimate will become more accurate!

The Multiverse is a hypothetical group of Universes which would probably be almost infinite in number. It would certainly be a number which we couldn’t wrap our small minds around. It is hypothetical because we can’t even come close to proving that exists, and in fact, we may never be able to do so.

But I think it should be mentioned here since there seem to be very compelling ideas which we have gleaned from our most advanced theoretical models in mathematics and physics, especially the many worlds interpretation of Quantum Theory, that it does actually exist. There is no point in giving any figure for the number of stars here since it would be completely meaningless. The only thing we need to know about the number of stars in the hypothetical Multiverse is that it is big – really BIG!