How might a pulsar appear to an observer?

If the Sun’s surface were cooler, how would its appearance change?

 What two forces are balanced in what we call gravitational equilibrium?

 How do we know that quasars are very distant objects?

Imagine that Earth were instantly replaced in its orbit by a speck of dust. Which statement best describes the subsequent orbital motion of that piece of dust?

What two things do we need to measure in order to determine a star’s luminosity using the inverse square law of light?

Picture1.jpgThe diagram above shows the life track of a 1 MSun protostar from the time it first begins to form until it reaches the main sequence, with four stages labeled. What is happening to the protostar’s surface temperature and luminosity during Stage 1, when gravity assembles the protostar from a collapsing cloud?

 Which of the following was an important reason why most ancient Greeks rejected the notion that the Earth orbits the Sun?

Which of the following statements correctly explains why galaxy collisions should have been more common in the past than they are today?

Which astronomer collected a lot of data on the position of the planets that helped Kepler to derive his three laws?