1. [2 pts] Draw an HR diagram that shows the location of the Main Sequence, Giant Branch, Horizontal Branch, and White Dwarfs. Be sure that you know how stars evolve on this diagram.
2. [2 pts] Constuct an HR diagram (on graph paper or with the aid of a computer plotting program - no freehand sketches acceptable) of the 25 brightest stars in the night sky, and of the 25 nearest stars to the Sun. Each plot should range from 10-5LSUN to 105LSUN on the y-axis, and from 2500K to 30000K on the x-axis. Remember that HR diagrams are plotted in logs, with red stars on the right.
3. [1 pt] What do the differences in these two diagrams tell us about the frequency of massive, hot stars vs. low mass, cool stars? Which diagram is a better representation of the true distribution of stars in our galaxy and why?
4. [2 pts] Use the equation L = constant*R2T4, where L is the stellar luminosity and R is the stellar radius, to show that objects with the same radii fall on a line in the HR diagram. [HINTS: remember that the equation of a line is y = mx+b, where m is the slope and b is the y-intercept; what variables in the HR diagram correspond to x and y?; review properties of logs]
5. [2 pts] Draw lines of 0.01 RSUN, 1 RSUN, and 100 RSUN in an HR diagram, and show where the Sun, Wolf 359, and Betelguese lie.
6. [1 pt]If the Sun were the size of Betelguese, what would it look like from the Earth?
The Brightest 25 Stars as seen at Night from Earth
The Closest 25 Stars
|Alpha Cen A||5800||1.6|
|Alpha Cen B||5250||0.45|
|Alpha Cen C||3000||6x10-5|
|61 Cyg A||4400||0.083|
|61 Cyg B||4000||0.040|