Describe the basic characteristics of stars’ orbits in the disk, halo, and bulge of our galaxy.

In broad terms, explain how the life of a high-mass star differs from that of a low-mass star. How do intermediate mass stars fit into this picture?

Describe the differences between normal spiral galaxies, barred spiral galaxies, and lenticular galaxies.

Explain why Cepheid variable stars are so useful for determining the distances of galaxies.

What is the minimum mass for a star, and why can’t objects with lower masses be true stars? What is a brown dwarf?

What is the defining characteristic of a main-sequence star? Briefly explain why massive main-sequence stars are more luminous and have hotter surfaces than less massive mainsequence stars.

We cannot use Hubble's law to measure the distances to nearby galaxies, because their random motions are larger than the overall expansion. Indeed, the closest galaxy to us, the Andromeda Galaxy, $2.5$ million light-years away, is approaching us at a speed of about $130 \mathrm{~km} / \mathrm{s}$. Ignoring the expansion, how soon will it and the Milky Way Galaxy collide?

In which group are the parts listed in order from oldest to youngest?

(1) solar system, Milky. Way Galaxy, universe

(2) Milky Way Galaxy, solar system, universe

(3) Universe, solar system, Milky Way Galaxy

(4) universe, Milky Way Galaxy, solar system

This tutorial will give you a better understanding of the size of the Milky Way Galaxy by investigating the distances and sizes of objects within the Milky Way Galaxy and outside the Milky Way Galaxy elsewhere in the universe. Below is a picture of a spiral galaxy similar to the Milky Way. Because we are located within the Milky Way, we are unable to take a picture of our entire galaxy from the outside. Let's assume that this picture represents our Milky Way Galaxy and has the dimensions labeled below. Note that in this picture, 1 centimeter $(\mathrm{cm})$ represents 10,000 light-years (ly); equivalently, you can use 1 millimeter ( $\mathrm{mm})$ to represent 1,000 light-years (ly).

The Sun's position in the Milky Way is shown in the picture above. What is the approximate distance from the Sun to the center of the Milky Way? Recall that $1 \mathrm{~cm}$ represents $10,000 \mathrm{ly}$.

How is a star’s apparent brightness related to its luminosity? Explain the inverse square law for light

What do scientists believe is at the center of the Milky Way galaxy?

Milky Way galaxy

Astronomers have estimated that the Milky Way galaxy contains $100$ billion stars. Express this number in scientific form.

Where are the stars with the most abundant metals in the Milky Way Galaxy: the visible halo, the disk, the spiral arms, or in the bulge?

Why is it so difficult to see if there are planets around other stars than the sun?