To the people who pointed out the reason I see so many stars, thanks. Your responses are in the spirit of good, rational discussion the likes of which the scientific method greatly benefits from. But to those of you who naysayed the BA, I say “No way!”

My poorly phrased question wasn’t Phil’s fault, it was my own. He took my rambling, poorly thought out question and turned it into a learning opportunity for us all. Thanks to you Dr. P!

From sea level, ignoring the aersol optical depth factor (AOD), the brightness of stars is reduced to about 86% due to scattering alone. Using the normal AOD factor range (0.2 to 0.5 per air mass), the brightness range is now about 50% to 70% of that seen from space.

From Mauna Kea (4200 meters), with no AOD, they see about 92% of AM0 (space view) when looking straight up, and about 90% at a 60 deg. alt.

The stellar magnitude loss from sea level is more than 0.6. Thus, from space, the number of stars will almost double the sea level viewers, and this is just in the view overhead. At 60 degress from zenith, four times as many stars should be seen from space in this region.

I doubt I am, Irishman. I seem to have lost an ability to cut-n-paste here, but at the very least, Google “how many stars can be seen” (or words to that effect) and you will come up with many good links stating something akin to “look up into the sky on a clear night, away from strong lights, and you will see a few thousand individual stars.” (roughly taken from an ESA site). I take “A few thousand” to be the 3,000 number.

On Earth, your horizon is roughly 8 miles away at sea level (very roughly). You do not, even in the best of situations, have even half of the celestial sphere above you. In that “limited” region of sky, it is generally assumed (again, very generally) that about 3k stars can be seen with the average naked eye.

As your altitude increases, your horizon increases and the number of visible stars increases as a direct result – just not as much as many people would think. Certainly not in the thousands until you have a completely unobscured view (which DOES give you a 360-degree view) – which does not happen unless you remove the horizon completely. Of course, this is generally theoretical and pretty much ignores the atmospheric effects well noted above.

I have never seen referenced ANYWHERE that the 3k stars reference number is for a full 360-degree ignore-the-Earth-is-there scenario. If you have a cite for that, and can paste it (unlike me!) I would love to see it.

You make the same point, I believe, in your last paragraph. Correct – the density does not (significantly, with suitably large values for significant) increase, but your horizon does – and assuming an equal distribution of unaided visibility, you therefore get more visible stars.

Just not more than 100% more – again ignoring all the mostly minimal atmospheric stuff. All other points well taken.

JC

Yes, you would see a bit more sky than ground. But that is irrelevant to the density of stars you would see, which is the actual question.

JackC said:
> Though I take the point regarding “not seeing zillions more” – your sight at the surface as has been noted is limited by the horizon. As you increase height, your horizon increases – until you get to the ultimate – space and beyond Earth. This in effect increases your horizon.

True.

> If we retain the number of 3000 visible stars at the surface, as your altitude above the surface increases, your scope of visible stars also increases. 300 more stars is a 10% increase.

False. You are misunderstanding the original number. 3000 stars means 3000 stars in the whole sky, 360 degrees around Earth. Your observable number is smaller because on the surface you cannot see the whole sky at one time.

The question is not how much sky can you see. It is about whether the sky you see has more dots in it, or brighter dots. That is an image density question, not an area question. Sure, at 30,000 ft you see a bit more area, but the density is not dramatically increased. In a space suit floating in space, you might be about to turn around and view the entire sky (except maybe some tiny fragment blocked by your pesky space vehicle), but it won’t have any where the dramatic difference of experience as going from an urban street to a remote field (like in the Austrailian outback).

First, extinction in the visual is 10%, not 2% as TBA said.

Second, this is looking straight up. Looking at 60 degrees to the zenith
(where most of the stars are), it increases to 20%. And more lower down.

[The fact that light pollution will probably be less on, say, a midocean part of an
intercontinental flight that almost anywhere on the Earth's surface will also help,
but I'm not sure by how much.]

So my guess, is that you can see an extra 600 or so stars.

Two factors to think about.

First, this assumes X% more light = X% more stars, but the actual increase
depends on the distribution of the number of stars per magnitude at 5th magnitude.

Second, can you only see 3000 stars? I think this is the number down to 5th, but the
fully adapted eye can see much deeper.