Questions: Introduction to Galaxies

Question 1

About how many stars does the Milky Way galaxy contain?

• A. A few thousand
• B. About one million
• C. 200 to 400 billion
• D. About one trillion

Answer: (C)

Current estimates place the Milky Way's star count at roughly 200-400 billion stars. Our Sun is just one ordinary star among this vast number. The Milky Way is a large galaxy, but not the largest — some elliptical galaxies contain over a trillion stars.

Question 2

What are the three main types of galaxies?

Model answer: Spiral galaxies (flat disk with arms of stars and gas winding outward from a central bulge — like the Milky Way), elliptical galaxies (smooth, oval-shaped collections of mostly older stars with little gas and dust), and irregular galaxies (no defined shape — often the result of gravitational interactions or collisions between galaxies).

This classification was first developed by Edwin Hubble in the 1920s. Spiral galaxies are actively forming new stars in their arms. Elliptical galaxies have largely used up or lost their gas and contain mostly old, red stars. Irregular galaxies are often small and are sometimes being torn apart by the gravity of a larger neighbor.

Question 3

The Milky Way band of light across the night sky is a distant galaxy far away from us.

• T. True
• F. False

Answer: False

The milky band of light across the sky IS our own galaxy — we are inside it. Because the Milky Way is a flat disk and we are located within that disk, we see the combined light of billions of distant stars when we look along the plane of the disk. We are looking through the galaxy edge-on. We cannot see the spiral shape from inside — just as you cannot see the shape of a forest when you are standing among the trees.