Jacob

Note: Express your answer as a number of times the original brightness of the Sun. A number greater than one means brighter, a number less than one means dimmer.

Note: Express your answer as a fraction of the change, so greater than one would be an increase, less than one would a decrease.

The Mars Orbiter is in a circular orbit just above the surface of Mars (radius of R = 3,400 km). The orbiter takes about 1.67 hours to complete an orbit. What was its orbital speed?

Suppose the distance to A from Earth is 225 Mpc, and the distance from B to Earth is 725 Mpc. In units of kilometers per second, what is the measured recessional velocity of B as seen by an observer on A?

Suppose the Universe were expanding twice as fast as we had originally thought, in other words, the Hubble constant were twice as large. How much older or younger a Universe would we live in now?

1. The Universe would be twice the age that we had originally thought.

2. The Universe would be the same age that we had originally thought.

3. The Universe would be √2 times older than we had originally thought.

4. The Universe would be √2 times younger than we had originally thought.

5. The Universe would be half the age that we had originally thought.

Suppose you measure the recessional velocity of a galaxy to be 20,000km/s moving away from us, what would an alien astronomer in that galaxy measure as the recessional velocity of the Milky Way?

1. 20,000 km/s moving towards them.

2. 40,000 km/s moving towards them.

3. 20,000 km/s moving away from them.

4. 40,000 km/s moving away from them.

5. 285 km/s moving away from them.

1. The idea that if we occupy a special place in the Universe, then it’s at the center.

2. The idea that if the Universe is infinitely old the stars should have all died out by now.

3. The conflict between the idea that if the Universe is infinite it should be filled with light and the reality that it is not.

4. The idea that the Universe had a beginning in time.

5. The idea that the Universe is expanding.

1. That redshift is a measure of how much time has sped up since the light was emitted.

2. That redshift means that dark matter causes the wavelength of light to be stretched with time.

3. That redshift is an indication of how much space itself has expanded since the light was emitted.

4. That redshift is merely a consequence of the motion of the galaxy.

5. That redshift is proportional to the recession velocity of a galaxy.

1. We see a redshift in the spectral lines of distance galaxies, and greater redshift for more distant galaxies.

2. We can see distant galaxies dissolve, pulled apart by the expansion of space.

3. We can see the disks of galaxies getting smaller over time.

4. We see the edge of the universe moving away from us.

5. All of these responses are evidence that the Universe is expanding.

Note: Consider the behavior of stars when galaxies collide, compared to the behavior of galaxies when clusters of galaxies collide.

1. Stars are denser than galaxies, on average.

2. When galaxy clusters collide, the number of galaxies involved measure dozens to thousands.

3. The distances between galaxies is comparable to their size.

4. When galaxies collide, the number of stars involved measure in the billions to hundreds of billions.

5. Galaxies are bigger than stars.

1. Chains of clusters of galaxies, merging where super clusters form, with voids in between.

2. Densely packed regions of galaxies and clusters widely separated from one another.

3. Random pockets of denser and less dense regions with no pattern whatsoever.

4. A completely uniform distribution of matter throughout the universe.

5. There is no matter in the Universe!

1. Galaxy cluster collisions show that dark matter follows the hot X-ray emitting gas, which is collisionless.

2. Galaxy cluster collisions show that dark matter follows the stars themselves, which are collisionless.

3. We have explored its properties in the laboratory and particle accelerators.

4. The flat rotation curve of spiral galaxies indicate that dark matter is collisionless.

5. The rapid motions of galaxies in rich clusters tell that dark matter is collisionless.

1. In the voids between galaxy clusters.

2. In the outer regions of a poor cluster.

3. In the central region of a rich cluster.

4. In the outer regions of a rich cluster.

5. In the inner region of a poor cluster.

1. The gas collides with the dark matter and the dark matter collides with the gas.

2. The gas collides with itself; the dark matter collides with itself.

3. The gas does not collide with itself; the dark matter does not collide with itself.

4. The gas collides with itself; the dark matter does not collide with itself.

5. The gas does not collide with itself; the dark matter collides with itself.

1. Elliptical and irregular; spiral and S0-type.

2. Spiral and irregular; elliptical and S0-type.

3. Elliptical and spiral; irregular.

4. Elliptical and S0-type; spiral and irregular.

5. Spiral; irregular.