# Worksheet: Hubble's Law

In this worksheet, we will practice using the formula v = H₀d (Hubble's law) to calculate the distance to faraway galaxies using the recession velocity.

Q1:

The galaxy NGC 87 has been observed to be moving away from Earth at a speed of 3,420 km/s. Using a value of 20.8 km/s/Mly for the value of the Hubble constant, find the distance between NGC 87 and Earth. Give your answer to 2 significant figures and in units of megalight-years.

Q2:

Edwin Hubble observed that the light from very distant galaxies was redshifted and that the farther away a galaxy was, the greater its redshift. What does this say about very distant galaxies?

• AThis says that all galaxies are moving closer together.
• BThis says that the farther away a galaxy is from Earth, the faster it is moving away from Earth.
• CThis says that the closer a galaxy is to Earth, the faster it is moving away from Earth.
• DThis says that the farther away a galaxy is from Earth, the faster it is moving toward Earth.
• EThis says that galaxies closer to Earth contain hotter stars which emit bluer light.

Q3:

Astronomers often measure the distance to faraway galaxies in units of megalight-years.

What is the unit symbol for a light-year?

• Aly
• BLY
• ClY
• DLy

What is the unit symbol for a megalight-year?

• AMlY
• BMLy
• CMly
• DMLY

How many light-years are there in a megalight-year?

Q4:

What is 240,000 ly in megalight-years?

Q5:

The Whirlpool Galaxy is 23 million light-years away from Earth. Using a value of 20.8 km/s/Mly for the value of the Hubble constant, find the value of the radial velocity of the Whirlpool Galaxy. Give your answer to 2 significant figures and in units of kilometers per second.

Q6:

The Hubble constant is an important constant in astronomy. It is often measured in units of kilometers per second per megalight-year.

Which of the following units could the Hubble constant also be expressed in?

• Am
• Bm−1
• Cs−1
• Dm2/s
• Em/s

Q7:

Hubble’s Law states that the radial velocity of a distant galaxy is proportional to its distance away from Earth. This can be expressed as , where is the radial velocity, is the distance away from Earth, and is the Hubble constant.

The most recent measurements of the Hubble constant find it to have a value of 20.8 km/s/Mly.

What is the radial velocity of a galaxy that is 50 Mly away from Earth? Give your answer in units of kilometers per second.

The Sunflower Galaxy is 27 Mly away from Earth. What is the radial velocity of the Sunflower Galaxy? Give your answer to 2 significant figures and in units of kilometers per second.

Q8:

What is 58,000 ly in kilolight-years?

Q9:

How many light-years are in 4.5 kly?

Q10:

How many light-years are in 3.2 Mly?