Question

Question 1) A Hertzsprung-Russell diagram shows stars on a plot of ________

a.	apparent brightness vs. temperature.
b.	luminosity vs. temperature.
c.	luminosity vs. distance.
d.	magnitude vs. apparent brightness.
e.	magnitude vs. temperature.

Question 2 The disagreement between the speed of stars near the edge of galaxies and the observable masses of the galaxies they are orbiting is explained by the presence of

a.	black holes.
b.	dark matter.
c.	dark energy.
d.	the cosmological constant.
e.	cosmic inflation.

Answer 1

a)

Luminosity Vs temperature

The Hertzsprung–Russell diagram, abbreviated as H–R diagram, HR diagram or HRD, is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities versus their stellar classifications or effective temperatures.

b)

dark matter

One point of evidence in support of dark matter is the way in which the speed of stars, gas and dust in a galaxy varies with their distance from the center of the galaxy, known as the galactic rotation curve. Most of the visible matter of a galaxy is concentrated near the center of a galaxy, so we would expect that more central stars should move much faster than stars on the outer rim. Thus the rotation curve should decrease with distance.