Questions of the Stars

I recently went out to enjoy the stars and questions kept popping into my head.  I'm going to go about answering these questions in a series of blog posts.  So let's get started!

How large does a star have to be for us to see it?

This was the question I wrote down, but it would be better asked, How much energy must a star give off for us to see it?

In researching this problem, I found this has been a multiple step problem for astronomers as well!  First, they used trigonometry to measure the distance of stars within 400 light years.  To do so, one must measure the angle of a star's location at two different moments on Earth (6 months apart so as to limit the measurement error).  This is the same principle for triangulation.  However, triangulation does not work for stars further than 400 light years due to too high of errors.  Astronomers began collecting data on the color spectrum for the various stars at known distances, which also depends on the energy emitted, or luminosity, by the stars.

Another problem to overcome is the fact light appears less intense the farther away the source is from the observer.  Astronomers have given the intensity of the light as viewed from Earth the name apparent magnitude.  Absolute magnitude is the luminosity of a star from 10 parsecs (1 parsec = 3.09 x 10^16 meters) away.

So a star's visibility depends on both the luminosity and distance the star is from Earth.  There is an equation relating apparent magnitude (m), absolute magnitude (M), and distance in parsecs (d) that can be used to answer such a question.

m - M = 5 log d - 5

For more information, click here!

Some time has passed since I dealt with higher level math, but I'm happy I now understand the basics of this.  Now I just need to figure out how astronomers acquire all the information, such as distance,  in order to calculate the star's absolute magnitude/luminosity.  Another question for another day!