Why do orbits of bulge stars bob up and down?

This diagram represents an edge-on view of our Milky Way Galaxy. Of the four labeled stars, which one is located in what we call the halo of the galaxy?

A protogalactic cloud with very little angular momentum is more likely to form an elliptical galaxy than a spiral galaxy.

A spacecraft is on a trajectory that happens to be taking it near a black hole. Which diagram shows how the spacecraft’s orbit will be affected?

What species absorbs photons in a protostar’s outer layers?

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?