a question of magnitude

TK274 · Post #1by **TK274** » 13.03.2003, 01:51

hello folks.
since I downloaded the great star catalogue (2 ml of stars) posted here on the forum, I have a question abou magnitude.
The magnitude limit sets the maximum star's magnitude our "eye" or camera can see.
I wonder what is the highest magnitude limit a human eye can see from a place in space without near light sources?

k77_99 · Post #2by **k77_99** » 13.03.2003, 11:41

Are you looking for a real, astronomical answer? If so, then the faintest magnitude seen from earth in an ideal location is about 6.5. Above the atmosphere that might go down a 1/5 a magnitude to 7, but I'm not sure. Remember it's a logaritmic scale. Believe it or not, even in an ideal location on Earth you can at best see only a few thousand stars in each hemisphere.

Hope that's what you're looking for.

k77_99 · Post #3by **k77_99** » 13.03.2003, 11:43

Are you looking for a real, astronomical answer? If so, then the faintest magnitude seen from earth in an ideal location is about 6.5. Above the atmosphere that might go down a 1/5 a magnitude to 7, but I'm not sure. Remember it's a logaritmic scale. Believe it or not, even in an ideal location on Earth you can at best see only a few thousand stars in each hemisphere.

Hope that's what you're looking for.

Guest · Post #4by **Guest** » 13.03.2003, 14:25

yes that's the answer I was looking for.
a correct astronomical answer.
so it's about 7 ..above the atmosphere on midnight.

I've asked this becouse I want to have a realistic view of the stars when I travel with celestia.
Now..since I'm very good with sound but I have not a lot of skills in phisics can somebody explain why the light of distant stars is less visible?
Is it for the redshift?

Buzz · Post #5by **Buzz** » 13.03.2003, 15:26

Light travels from a star in all directions. The further from the star, the larger the area that is "lit" by the same amount of light. The intensity is reduced 4 times every time the distance to the star is doubled.

Redfish · Post #6by **Redfish** » 13.03.2003, 16:03

The best and biggest telescopes on earth(dunno about hubble) can see up to magnitude 21, so imagine, what it would look like, if we'd have stars as faint as those. Also the fainter stars are, the more numerous they appear to be.

TK274 · Post #7by **TK274** » 14.03.2003, 11:26

Buzz wrote:Light travels from a star in all directions. The further from the star, the larger the area that is "lit" by the same amount of light. The intensity is reduced 4 times every time the distance to the star is doubled.

Okay!! I've got it!
I't exactly the same as for audio Waves (sound)
so:

Light= Absolute Magnitude/4 Pi r^2
and that's explain why magnitude is a Log scale..just as for sound we use dB wich is a Log scale too.

Thanks for the kind reply

Buzz · Post #8by **Buzz** » 14.03.2003, 11:48

You're welcome! But another remark: the log scale is not because of the 1/r^2 dependance, but because of the way humans experience different sound and light levels. Our ears and eyes work logaritmic!

tk274 --- · Post #9by **tk274 ---** » 14.03.2003, 14:25

Buzz wrote:You're welcome! But another remark: the log scale is not because of the 1/r^2 dependance, but because of the way humans experience different sound and light levels. Our ears and eyes work logaritmic!

yes that's correct
I just explained myself bad..

Guest · Post #10by **Guest** » 17.03.2003, 14:37

Redfish wrote:The best and biggest telescopes on earth(dunno about hubble) can see up to magnitude 21, so imagine, what it would look like, if we'd have stars as faint as those. Also the fainter stars are, the more numerous they appear to be.

The Hubble Deep Field went to about magnitude 28 with a signal-to-noise ratio of 10. The advent of the Advanced Camera for Surveys means that such limits can be reached with much shorter integration times.