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Free Astrophysics Notes (1 Viewer)

Drsoccerball

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Can i ask something about your notes?
Is this statement true? i thought it was the other way around ?

"In general, stars with a negative B-V colour index will appear more blue and stars with a positive B-V colour index will appear more yellow, orange or red"
EDIT: My bad its magnitude ahahahaha
 
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Drsoccerball

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"Therefore, if two stars have the same apparent magnitude but are different distances away from Earth, the closer star will have an absolute magnitude smaller than that of the star further away."

Smaller absolute magnitude = Brighter
Doesn't make sense that the closer one is brighter...?
 

InteGrand

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"Therefore, if two stars have the same apparent magnitude but are different distances away from Earth, the closer star will have an absolute magnitude smaller than that of the star further away."

Smaller absolute magnitude = Brighter
Doesn't make sense that the closer one is brighter...?
No, absolute magnitude is the intrinsic brightness of the star, apparent magnitude is the perceived brightness by an observer on Earth. So when we see a star as being "bright" from Earth, we are referring to its apparent magnitude.

Obviously intuitively if two stars appear equally bright (apparent brightness) but are difference distance away, the one that is further away is more "powerful" (i.e. higher absolute magnitude, more intrinsically bright) than the closer one.
 
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Drsoccerball

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No, absolute magnitude is the intrinsic brightness of the star, apparent magnitude is the perceived brightness by an observer on Earth. So when we see a star as being "bright" from Earth, we are referring to its apparent magnitude.
Absolute magnitude is the brightness perceived if the star was at a distance of 10 Pc... The lower the magnitude the brighter the star. So if something was -2 in apparent magnitude it outshines another star of apparent magnitude of X So it would make logical sense that the one further away assuming both appear the same in brightness has a lower absolute magnitude.
 

Drsoccerball

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Obviously intuitively if two stars appear equally bright (apparent brightness) but are difference distance away, the one that is further away is more "powerful" (i.e. higher absolute magnitude, more intrinsically bright) than the closer one.
But magnitude is different to brightness. The lower the magnitude the brighter it is.
 

InteGrand

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But magnitude is different to brightness. The lower the magnitude the brighter it is.
By "smaller" in the notes, maybe it meant smaller as in smaller absolute value, e.g. -1 is smaller than -4, in the sense than |-1| < |-4|.
 

leehuan

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The less positive magnitude is brighter. There.
 

leehuan

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What the hell. I just realised you were another astrophysicist who became an actuary :p
 

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