Most active galactic nuclei are found at large distances from us, with relatively few nearby. What does this imply?

The red evolutionary track illustrated in the figure above (similar to fig 19.6 in your textbook), that goes from point 4 to 5 to 6 to 7 shows:

Consider an atom of carbon in which the nucleus contains 6 protons and 7 neutrons. What is its atomic number and atomic mass number?

Both photos show the same field of view containing a star-forming molecular cloud. One of the photos was taken in visible light and the other in infrared light. Which one is the visible-light photo, and how do you know?

Why is the spectral sequence of stars not alphabetical? 

Briefly describe how a star forms. Explain why stars form only in molecular clouds, the coldest, densest parts of the interstellar medium.

Which of the following statements about globular clusters is false?

Each of the following describes an “Atom 1” and an “Atom 2.” In which case are the two atoms isotopes of each other?

Cluster ages can be determined from

This H-R diagram shows the life track of a 1 MSun star from the time it first becomes a main-sequence star. Which numbered point represents the star when it has both hydrogen-burning and helium-burning shells around an inert carbon core?