Jessica Brandon Final

1.     How does solar activity vary with time?

A. The sunspot cycle , or the variation in the number of sunspots on the Sun's surface has an average period of 11 years. The magnetic field flip-flops every 11 years or so, resulting in a 22-year magnetic cycle. Sunspots first appear at mid-latitudes at solar minimum, then become increasingly more common near the Sun's equator as the next minimum approaches, and sometimes seem to be absent altogether.

2.     How do we measure stellar masses?

B. We can measure the masses of stars in binary star systems using Newton's version of Kepler's third law if we know the orbital period and separation of the two stars.

3.     How do stars form?

C. Stars are born in cold, relatively dense molecular clouds. As a cloud fragment collapses under gravity, it becomes a rapidly rotating protostar surrounded by a spinning disk of gas in which planets may form. The protostar may also fire jets of matter outward along its poles.

4.     What is a neutron star?           

D. A neutron star is the ball of neutrons created by the collapse of the iron core in a massive star supernova. It resembles a giant atomic nucleus 10 kilometers in radius and with more mass than the Sun.

5.     How do halo stars tell us about our galaxy's history?

A. The halo generally contains only old, low-mass stars that have a much smaller proportion of heavy elements than stars in the disk. Halo stars therefore must have formed early in the galaxy's history, before the gas settled into a disk.

6.     How are galaxies grouped together?

B. Spiral galaxies tend to collect in groups that contain up to several dozen galaxies. Elliptical galaxies are more common in clusters of galaxies, which contain hundreds to thousands of galaxies, all bound together by gravity.

7.     What is the role of dark matter in galaxy formation?

C. Because most of a galaxy's mass is in the form of dark matter, the gravity of that dark matter is probably what formed protogalactic clouds and galaxies from slight density enhancements in the early universe.

8.     What are the largest structures in the universe?

B. Galaxies appear to be distributed in gigantic chains and sheets that surround great voids. These giant structures trace their origin directly back to regions of slightly enhanced density early in time.

9.     Will the universe continue expanding forever?

A. Even before we consider the possibility of dark energy, the evidence points to eternal expansion. The critical density is the average matter density the universe would need for the strength of gravity to eventually halt the expansion. The overall matter density of the universe appears to be only about 25% of the critical density.

10. Is the expansion of the universe accelerating?

D. Observations of distant white dwarfs indicate that the expansion is speeding up. No one knows the nature of the mysterious force due to dark energy that could be causing this acceleration.