Absolute magnitude

[neoterryjoe]

Absolute magnitude of a star is a measure of luminosity or how much light the star is actually radiating into the space. Astronomers define a star's absolute magnitude as the apparent magnitude the star would have if it were located at a standard distance of 10parsecs from Earth. How do they calculate the absolute magnitude of a star?

There is an equation relating distances from magnitude.

m - M = 5log( D / 10 )
where m - apparent magnitude
M - absolute magnitude
D - distance of star in parsecs

Can this be used to calulate the absolute magnitude as this equation is used for calculating distances of stars? If so, are there any other more accurate methods of measuring distances of stars other than the parallax method? If not, how is the absolute magnitude measured/calculated?

Another question: How is apparent magnitude related to luminosity(apparent brightness)? Any ratio?

Thanks for any suggestions/help.

[chrisyeo]

1. Distance and luminosity of an object is related by an inverse square law. If you know the apparent magnitude and the distance, you can calculate the absolute magnitude (defined at 10pc).

2. Yes, this equation can be used if you know D.
Astronomers have various ways of determining distance. Try searching for the "distance pyramid" online. Besides direct parallax, spectroscopic parallax and variable stars are used to determine distance of stars.

3. Luminosity is not apparent brightness but its absolute or intrinsic brightness. Apparent magnitude is related to apparent brightness in the following way: Intensity(brightness) is proportional to 100^(M/5). This is related to your equation above. Please see: http://outreach.atnf.csiro.au/education ... osity.html

Hope this helps,
Chris

[neoterryjoe]

Hi!

Luminosity is absolute brightness? Or is it the reference book that I read is wrong? Hmmm... :?: :!: :?

Thanks a lot anyway!