Name:
Classifying Stars by Temperature and Brightness
Introduction:
If you were to plot a graph of height vs. mass for a random selection of people, what might you expect to see? Because most people weigh more the taller they are, we expect to see a correlation. While there may be some exceptions to this relation, for the most part it is true. Amazingly enough, when you plot the brightness of a star vs. its temperature, another type of correlation becomes apparent. In this activity, we will look for the correlations between a star’s brightness, color and size.
Properties of Stars:
Magnitude: There are two ways of measuring the luminosity (brightness) of a star, by apparent magnitude and by absolute magnitude. Apparent magnitude is the brightness of the star based on how we perceive it from the Earth. Absolute magnitude is based on the intrinsic brightness of the star. For this lab, we will use apparent magnitude. This means that the stars luminosity is compared to the sun’s luminosity. If a star has a value greater than 1, it means it is that many times the sun’s luminosity. A value less than one means it is that fraction of the sun’s value.
Temperature: The temperature of stars is often measured in Kelvin (not degrees Celsius). Kelvin is very similar to Celcius, but whereas 0 degrees Celcius is the freezing point of water, 0 Kelvin is absolute zero...the freezing point of everything! At this temperature everything freezes and stops moving, even electrons around the nucleus of an atom! For this lab, we will keep the temperature in Celsius.
Lab Procedure:
1. Notice that each star has a name, a color, a temperature and a luminosity value.
2. You will create a table for the stars from the following website: http://www.hmxearthscience.com/hr_diagram_lab.html#lightbox/0/
3. You then classify each star according to its Spectral Classes
Star Name / Luminosity / Temperature / Color / Spectral Class4. Locate these stars on the HR Diagram in the spectral classes handout.