What is the relationship between brightness and distance of a star?

Answer 1

The amount of light we receive from a star - other things being equal - is inversely proportional to the square of the distance. For example, from a star that is ten times as far from us as another star (of the same type), we will only receive 1/100 of the light that we receive from the closer star.

The "actual" brightness of the star is called "absolute magnitude". It is calculated as if all stars were at the same distance, so that we can compare stars directly. The "apparent magnitude" of the star is how bright it appears in our own night sky.

Two stars can have the same apparent magnitude even though one star is small, dim and close, while the other star is huge, bright and distant.

Answer 2

As far as astronomy is concerned, not much! However, magnitude uses an actual, mathematically-defined system whereas brightness is a more 'fuzzy' idea. For instance, you could say 'Sirius is brighter than Polaris' (which is true!) but magnitude enables you to actually say how much brighter it is. The magnitude of Sirius is about -1.5 whereas Polaris, though slightly variable, is about 2.1.

In case you don't know, the magnitude system works 'backwards' so to speak, so the smaller the number the brighter the star. Sirius is so bright its magnitude value is negative. The magnitude of the Sun is about -26.

To complicate things, astronomers use several magnitude systems. The one above (and the one I guess you're asking about) is called APPARENT magnitude - that is, a measure of how bright a star looks in the sky. But Sirius only appears brighter than Polaris because it's much, much closer to us (8 light years instead of Polaris's 600-odd lightyears). To account for this, astronomers use another magnitude system called ABSOLUTE magnitude. We choose a default distance of 10 parsecs (about 32 lightyears) and work out how bright a star would be if it were at this distance. It's a way of eliminating the 'closer is brighter' effect I just mentioned, and gives a guide to the actual physical parameters of each star.

Answer 3

The answer is lengthy, the answer is "Black Body Radiation". In short: The hotter the object is, the higher the frequency/shorter the wavelength of the spectrum is emitted.

Infrared is the lowest temperature, then a black body transitions roughly through red, orange, yellow to white. Not green or blue, due to color mixing of multiple frequencies.

Answer 4

one is light the other is how fast it travles