# How to Determine Absolute Magnitude

1. Jan 15, 2014

### ckirmser

Hello, all.

I'm trying to find an equation to determine a star's absolute magnitude in order to populate a table of stellar characteristics.

Unfortunately, every formula I've run across requires a star's apparent magnitude and that requires knowing how far the star is from the observer.

But, I need a general case formula.

Basically, I have a star catalog, but many of the stars do not have a complete classification; perhaps they are listed as AIII, or M4.5, or, simply K. I'm going to provide a "best guess" at the full classification, by taking the parts that are known, and using the absolute magnitude to finesse the value.

For example, suppose I have a star listed as A0 with an absolute magnitude of -3.36.

By the data I already have, A0Ib has an absolute magnitude of -5.3, A0II has -3.4 and A0III has -0.3.

Using averages to get the boundary between each entry - not perfect, but it's the best I have - I find that -3.36 falls within the boundary of -4.35 to -1.85 for an A0II star. So, I correct the incomplete entry to A0II.

The problem is with star classes for which the table is incomplete; like classes C, S, WN, etc. I have the temperatures for these classes and their radii in solar units, but not their magnitudes.

Any thoughts?

2. Jan 16, 2014

### ckirmser

OK, I think I've found the answer. From further reading, I've found that absolute magnitude is simply the apparent magnitude at ten parsecs. So, I just plug in that constant distance to the formulas I've found.