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In the best sky conditions, we can see about 44,000 stars in the sky. But what if I am located around Equator area? How many stars I can see?

From what I know, the number of stars I can see should be far less ( I don't know why, though). Is it true? If yes, why?

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It would have been better if in your question you gave some basis for what you believed eg a reference - rather than just saying 'from what I know' – Jeremy Jun 17 '14 at 11:30
up vote 3 down vote accepted

The numbers you're quoting are extreme, more like a theoretical limit, and meaningless in practice.

The 44k number would be true if you assume a limiting magnitude of 8. There aren't many people alive today who have seen at least one object at mag +8. This is not so much due to vision problems (although that may be important for some people), as to the fact that a mag +8 sky is an incredibly rare occurrence today due to light pollution.

If you live on a continent with a low population density (such as North America, Australia, or the remote parts of Asia), then yes, maybe you have a chance of catching a mag +8 sky - if you drive far out into the desert, many hours away from any city or town. But if you live in Europe or the like, forget it.

Furthermore, the 44k number is obtained by assuming the mag 8 conditions, and then counting all known objects in the sky whose brightness exceeds that limit. It is very unlikely that any one person would see them all in one lifetime. Seeing even a single star at mag 8 can be a difficult undertaking for many people, even in ideal conditions.

It is very hard to quote a number, since it is so much dependent on light pollution, transparency, visual acuity of the observer (nearsighted people can't focus well enough to see very faint stars), the observer's age (acuity gets worse with age), the observer's experience (visual astronomers with years of experience will be able to see much fainter stars because they know how to look), etc.

If you're on a farm, away from cities, in a place with reasonably low light pollution, and your eyes are good, and you've been sitting in perfect pitch black darkness for at least 30 minutes prior - when you look up you can reasonably expect to see a few thousand objects, mostly stars. Keep looking, and after a while you will distinguish one or two thousand more stars, very faint, that you could not see at first sight. Practice this steadily for a few years, and you'll add maybe another thousand; but you won't be able to see those all at once - only one at a time.

Now travel to the Cerro Tololo site in Chile, up in the mountaineous desert, zero light pollution, excellent transparency, and you'll multiply all those numbers by a factor of 2x ... 5x.

As you can see, the numbers are very flexible because there are so many factors involved. You can't just slap a 44k label on it and call it a day; that doesn't make any sense in reality. Astronomers know that the pure magnitude number doesn't mean much by itself, because it is just one factor among many.

In a place with very high light pollution (like where I live, in the middle of a large, dense, sprawling urban area in California), you'd be lucky if you can see a hundred stars at night.

Or, in a place with zero light pollution, shine a flashlight into someone's face, and you've temporarily blinded them. You've reduced the number of stars they could see by an order of magnitude for the next half hour (night vision gradually recovers, and it takes 30 minutes to fully recover, according to US military manuals and visual astronomers practice).

Now, Equator versus poles.

The spin axis of the Earth has a fixed direction in space. The north - south axis always points at the same places in the sky, near Polaris in the north, and near the Southern Cross in the south.

For this reason, at the North Pole, you only ever see half the sky - the northern half, centered on Polaris. At the South Pole, you only see the other half. You'll never see Polaris from Australia.

At the Equator, you pretty much see the whole sky - not all at once, of course, but as the Earth rotates, it gradually exposes all parts of the sky at different times. However, the parts near Polaris and near the Southern Cross are always low in the sky and a bit hard to see.

So, bottom line is this:

In any place on Earth, in any given instant, you see exactly half of the sky. At the poles, that half is all you ever see. At the Equator, if you're patient, you'll eventually see the whole sky in time, as the Earth rotates and gradually exposes different parts of the sky at different times.

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No, it isn't true. In fact over time you will see more stars at the equator than at any other latitude. The further you go towards the poles, the more stars are never seen because the planet gets in the way.

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