module 20 lesson 3

Dr. X believes that the Hubble constant is H0 = 55 km/s/Mpc. Dr. Y believes it is H0 = 80 km/s/Mpc. Which statement below automatically follows?

Dr. X believes that the universe is older than Dr. Y believes.

What is the most accurate way to determine the distance to a nearby galaxy?

using Cepheid variables

What is the most accurate way to determine the distance to a very distant irregular galaxy?

using a Type Ia supernova as a standard candle

Recall that Hubble's law is written v = H0d, where v is the recession velocity of a galaxy located a distance d away from us, and H0 is Hubble's constant. Suppose H0 = 65 km/s/Mpc. How fast would a galaxy located 500 megaparsecs distant be receding from us?

32,500 km/s

Why can't we see past the cosmological horizon?

Beyond the cosmological horizon, we are looking back to a time before the universe had formed.

Why are Cepheid variables important?

Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.

What is Hubble's law?

The recession velocity of a galaxy is directly proportional to its distance from us.

What makes Type Ia supernova good standard candles? (mark all that apply)

They are very bright, so they can be used to determine the distances to galaxies billions of light-years away.

What is the primary practical difficulty that limits the use of Hubble's law for measuring distances?

We do not know Hubble's constant very accurately yet.

What is a standard candle?

an object for which we are likely to know the true luminosity

Based on current estimates of the value of Hubble's constant, how old is the universe?

between 12 and 16 billion years old

How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the "spiral nebulae" were actually entire galaxies?

from the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that is was far outside the Milky Way Galaxy

How did Edwin Hubble measure the distance to the Andromeda Galaxy?

he applied the period-luminosity relation to Cepheid variables

Why is the Hyades Cluster important for building up a catalog of the true luminosities of main-sequence stars?

it is close enough to us that the distance to the cluster stars can be found by stellar parallax

Which of the following sequences lists the methods for determining distance in the correct order from nearest to farthest?

parallax, main-sequence fitting, Cepheid variables, Hubble's law

What is the most accurate way to determine the distance to a nearby star?

stellar parallax

Which of the following is a consequence of Hubble's Law?

the more distant a galaxy is from us, the faster it moves away from us

What two quantities did Edwin Hubble plot against each other to discover the expansion of the Universe?

velocity and distance

Type Ia supernovae are good standard candles for distance measurements for all the following reasons except which?

white-dwarf supernovae occur only among young and extremely bright stars.