rlow wrote:Sharp optics you have, chaosknight; you are spot on. That was indeed some sloppy work I did. Next time I better open my eyes and think twice before I consider to post here.
Yes, it should have read as "...or the radius of the Earth' orbit."
Hahaaa.....well....to be fair the definition i posted abt 1 AU subtended at 1 arc sec isn't so complete either.
mm..i've always thought the earth's orbit is not circular?
that was the reason why Kepler initially could not reconcile his readings with his calculation when he was developing hisl laws on planetary motion..the orbit were elliptical?
rich
The Boldly Go Where No Meade Has Gone Before Captain, RSS Enterprise NCC1701R United Federation of the Planets
rlow wrote:Sharp optics you have, chaosknight; you are spot on. That was indeed some sloppy work I did. Next time I better open my eyes and think twice before I consider to post here.
Yes, it should have read as "...or the radius of the Earth' orbit."
Hahaaa.....well....to be fair the definition i posted abt 1 AU subtended at 1 arc sec isn't so complete either.
mm..i've always thought the earth's orbit is not circular?
that was the reason why Kepler initially could not reconcile his readings with his calculation when he was developing hisl laws on planetary motion..the orbit were elliptical?
rich
Yes. But since the Earth's orbital ellipse has very low eccentricity, 1AU is loosely taken as the radius of the orbital path. If i remember correctly, the exact definition of 1AU is the semi-major axis of the Earth's orbital path.
Haha.. actually, in numbers.. Earth's orbit eccentricity is 0.98, with 1 being a perfect circle and 0 being super eccentric. So you might wanna safely assume the semi-major and minor axes of Earth's orbit to be the same.. oops, i think getting quite off-topic here..
Anyway back to it, I suppose we had better just remember 1 parsec=3.26 light years, it's all the better than arguing the definition of a parsec, eh So, putting the star a parsec away from us, that's the real magnitude (take not not apparent) of the star. That's the definition of real magnitude, don't ask why they used one parsec as the standard. They just did.
zong wrote:Haha.. actually, in numbers.. Earth's orbit eccentricity is 0.98, with 1 being a perfect circle and 0 being super eccentric. So you might wanna safely assume the semi-major and minor axes of Earth's orbit to be the same.. oops, i think getting quite off-topic here..
Anyway back to it, I suppose we had better just remember 1 parsec=3.26 light years, it's all the better than arguing the definition of a parsec, eh So, putting the star a parsec away from us, that's the real magnitude (take not not apparent) of the star. That's the definition of real magnitude, don't ask why they used one parsec as the standard. They just did.
Real magnitude = absolute magnitude?
Is the standard 1 parsec?
Oops, sorry for wrong info about the distance set for real magnitude.. :oops: guess i have too much school stuff cramped into my brains already..
I see quite some people confused about apparent and real magnitude.
Imagine a bright source very near (1m) to you. Is it very very bright? Now bring it 10m from you. It should look dimmer now right?
Vice versa, let's imagine a very dim object 100m away. It looks real dim. But if you bring it to 10m from you, it looks brighter!
Scientists therefore have to put a standard on how to measure brightness. They set the distance to 10 parsecs, ie 32.6 light years, for the measurement of brightness. Therefore, to measure the real magnitude of any body, you have to put it 10 parsecs away from you. This is the real comparison of brightness of the different bodies.
However, for apparent magnitude, it just measures the brightness WITHOUT taking into account distance. This means, although the sun is dimmer than Sirius, it registers a lower magnitude (ie. brighter) than Sirius. Please take note that apparent and real magnitudes are really different.
However, I have read a formula somewhere that relates these two. I have forgotten it, maybe someone else could enlighten us? ;)
So, putting the star a parsec away from us, that's the real magnitude (take not not apparent) of the star. That's the definition of real magnitude, don't ask why they used one parsec as the standard. They just did. 
"The universe is composed mainly of hydrogen and ignorance."