HW 11: The Expanding Universe

How did Hubble initially determine distances to individual stars on the spiral arms of Andromeda galaxy?

Cepheid Variables

Who is first credited with the discovery that galaxies, with the exception of the most nearby galaxies, are moving away from us by obtaining their redshift from stellar spectra in 1914?

Vesto Slipher

What is the law that states that “the farther a galaxy is from us, the faster it is moving away from us”?

Hubble's Law

What is the fundamental knowledge gained from Hubble's Law?

The universe is expanding

What is the model of the expansion of the universe?

The universe is uniformly expanding at all points

How do scientists estimate the age of the universe?

From the distance to any galaxy, divided by the speed of recession (time = distance/velocity).

What does it mean to say that our universe is expanding?

 Space itself is expanding

When we look at a very distant galaxy, billions of light years away, we see it…

When it and the whole universe was younge

What do we see when we look beyond the cosmological horizon?

We cannot look beyond the cosmological horizon because we cannot look back at time before the universe began.

In 1994, the Hubble Space Telescope observed a seemingly empty patch of the sky near the Big Dipper and obtained the remarkable image of a multitude of galaxies at several distances after nearly 10 days of exposure. What is this image called?

Hubble Deep Field

Suppose you measure the brightness and period of several Cepheid variable stars in Galaxy A and Galaxy B. You find that all the Cepheid variables in Galaxy A are approximately 25 times as bright (apparent brightness) as Cepheid variables with similar periods in Galaxy B. What can you conclude about the distances of these galaxies?

Galaxy B is 5 times as far away as Galaxy A.

 A cluster of galaxies is observed to have a recessional velocity of 60,000 km/s. Find the distance to the cluster. (Assume a Hubble constant of 22 km/s per million light-years.)

2.7 x 10³Mly