Name: ________________________ | DUE 11/27 |
ID number: ________________________ |

Hubble's law states that the recession velocity of a distant galaxy
is directly proportional to its distance:

Here

**1.** The peculiar galaxy NGC 7252 has a distance *d* =
47 Mpc . What is its recession velocity?

(Note: **show your work** to receive full credit! Make sure to
give the units of your result.)

**2.** The galaxy cluster Abel 2218 has a recession velocity
*v* = 54,000 km/s . What is its distance?

(Again, show your work, and give the units of your result.)

**3.** Suppose you know that Hubble's law is valid but you
don't know the value of Hubble's constant *H*_{0} . What
observations would you need to estimate the value of
*H*_{0} ?

**4.** Suppose you didn't even know if Hubble's law is valid
(this also implies that you don't know what value *H*_{0}
might have). What observations would you need to test Hubble's
law?

Joshua E. Barnes (barnes@ifa.hawaii.edu)

Last modified: November 19, 2001

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