Let's say that the number density of galaxies in the universe is, on average, 3 × 10–68 galaxies/m3. If astronomers could observe all galaxies out to a distance of 1010 light-years, how many galaxies would they find? (Note that there are 1016 meters in 1 light-year.)

Your friends are talking about Olber's Paradox: Friend 1: When the universe was quite young, it was also quite small, and therefore light was trapped inside the universe. This is why we don't see light from the edge of the universe in every direction. Friend 2: No, Olber's Paradox describes only light from stars, not from galaxies, and why you can't use light from distant stars to see at night. Friend 3: You're both right and you're both wrong. The paradox concerns itself with the expansion of the universe, and explains why light from the early universe was able to be released. Are any of them right, in part or in whole?

On a 1-to-10^19 scale our Milky Way galaxy would just about fit on a soccer field. On this scale, how far is the distance from the sun to alpha centauri (one of the closest stars to the sun, at a distance of 4.4 light years).

An astronomer in an imaginary Universe observes a small patch of the sky (0.005% of the total) with very deep observations and finds one million galaxies. How many galaxies can they estimate to be present in the whole Universe? 10 billion 20 billion 50 billion O 70 billion

Figure 2 shows the "rotation curve" of NGC 2742. It plots the “radial velocity (V)" (how fast material is moving either toward or away from us) that is measured for objects at different distances (R = radius") from the center of the galaxy. The center of the galaxy is at 0 kpc (kiloparsecs) with a speed of 9 km/sec away from us. (These velocities have been corrected for the observed tilt of the galaxy and represent true orbital velocities of the stars and gas.) 200 100 U4779 -100 As you can see, one side of the galaxy is moving with a negative velocity (spinning toward us), while the other side has a positive velocity (spinning away from us). Using Newton's gravity equation, we will be able to determine the gravitational mass of the entire galaxy and how the mass varies versus distance from the galaxy's center. -200 -8 8 -4 Radius (kpc) Read the following text carefully and follow the instructions: Select five radii spaced evenly from 0-10 kpc across the galaxy. Your selections should…

If a quasar is 2,000 times more luminous than an entire galaxy, what is the absolute magnitude of such a quasar?  Note: The absolute magnitude of the Milky Way Galaxy is about −21. Hint: Use the formula for magnitudes and flux ratios,