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Is the brightness of a star it's flux?

I saw an mcq which said that the brightness depends on the distance to the star and the luminosity so I'm asking to confirm.
Reply 1
Luminosity is the total power output of a star. Think power = intensity x area. Intensity or "flux" is basically the power at a certain spherical distance away.
So the sun will have an intensity of a massive figure, but here on earth the intensity is much less as it decreases by 4πr^2
Original post by Presto
I saw an mcq which said that the brightness depends on the distance to the star and the luminosity so I'm asking to confirm.
Reply 2
Original post by thoque
Luminosity is the total power output of a star. Think power = intensity x area. Intensity or "flux" is basically the power at a certain spherical distance away.
So the sun will have an intensity of a massive figure, but here on earth the intensity is much less as it decreases by 4πr^2


Sorry but is that a no then?
Reply 3
could you clarify what mcq means, im confused. but yes, intensity does depend on distance and luminosity
Original post by Presto
Sorry but is that a no then?
Reply 4
Original post by thoque
could you clarify what mcq means, im confused. but yes, intensity does depend on distance and luminosity

Multiple choice question
So basically intensity, flux and brightness are all different words defining the same thing, right?
Reply 5
Well yes, but actually no.
nah im memeing they are all the same basically.
Original post by Presto
Multiple choice question
So basically intensity, flux and brightness are all different words defining the same thing, right?
Reply 6
Original post by thoque
Well yes, but actually no.
nah im memeing they are all the same basically.

Are you sure?
Reply 7
fairly, yes, although its a fine detail and one that examiners will probably give you marks for either one. Just make sure you dont mix up luminosity and intensity.
Original post by Presto
Are you sure?
Reply 8
Original post by thoque
fairly, yes, although its a fine detail and one that examiners will probably give you marks for either one. Just make sure you dont mix up luminosity and intensity.

Ah ok thanks :smile:
Original post by Presto
I saw an mcq which said that the brightness depends on the distance to the star and the luminosity so I'm asking to confirm.


Original post by Presto
Multiple choice question
So basically intensity, flux and brightness are all different words defining the same thing, right?



I would say “brightness” is related to the flux. See the link(s) below.
https://physics.stackexchange.com/questions/191678/brightness-of-light-sources
https://www.cv.nrao.edu/course/astr534/Brightness.html
http://star-www.rl.ac.uk/docs/sc6.htx/sc6se5.html


However, at A level, we tend to take a simplified view:

The brightness b of a star:

b=L4πr2 b = \dfrac{L}{4 \pi r^2 }

where L is the luminosity of a star is the amount of energy in joules it actually radiates per second (that is, its power).
Reply 10
Original post by Eimmanuel
I would say “brightness” is related to the flux. See the link(s) below.
https://physics.stackexchange.com/questions/191678/brightness-of-light-sources
https://www.cv.nrao.edu/course/astr534/Brightness.html
http://star-www.rl.ac.uk/docs/sc6.htx/sc6se5.html


However, at A level, we tend to take a simplified view:

The brightness b of a star:


b=L4πr2 b = \dfrac{L}{4 \pi r^2 }


where L is the luminosity of a star is the amount of energy in joules it actually radiates per second (that is, its power).


In Edexcel there's
F=L4πd2 F= \dfrac{L}{4 \pi d^2 }
So the flux is the brightness right?
Original post by Presto
In Edexcel there's
F=L4πd2 F= \dfrac{L}{4 \pi d^2 }
So the flux is the brightness right?


"Yes". But don't take it beyond A level. :smile:
Reply 12
Original post by Eimmanuel
"Yes". But don't take it beyond A level. :smile:

XD
Thank you :smile:
I guess i saw this unit 5 physics...

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