SIERRA COLLEGE OBSERVATIONAL ASTRONOMY

LABORATORY EXERCISE

NUMBER V.V. TITLE: Hubble Redshift-Distance Relation

Adapted from ‘CLEA’, a project sponsored in part by NSF

DATE- PRINT NAME/S AND INITIAL BELOW: GROUP

DAY-

LOCATION

Objective: Plot ‘d’ (distance) vs. ‘V’ (recession velocity) for 5 galaxy fields (clusters) on the graph provided (see back of this sheet) and determine ‘H’, the Hubble Constant. Then, calculate the age of the universe (1/H) in years.

Procedure:

1) Refer to page 492 in textbook (Arny) for details on the Hubble expansion of galaxies.

2) Instructor will demonstrate the use of the Computer Simulated Observatory for the collection of galactic spectral information.

3) Instructor will discuss how to use the formula d = 10^(m-M+5)/5 to calculate the distance ‘d’ (in parsecs) to a galaxy given the galaxy’s ‘m’ (apparent magnitude) and ‘M’ (absolute magnitude).

4) Use the Computer Simulated Observatory to determine l_shifted for the calcium k absorption line of any galaxy in each of the 5 galaxy fields, while recording the s/n (signal-to-noise ratio) and m values [Note: Be sure your s/n ratio exceeds 10 before recording data.].

5) Determine d for each galaxy field [Note: In the table below, the distance is recorded in Mpc (megaparsecs)].

6) Calculate Dl and V (= c Dl/l_o, where c = 300,000 km/sec, and Dl = l_shifted - l_o) for each absorption line.

7) Plot V vs d on the graph for each galaxy field (5 total data points) and continue procedure on back page.

Galaxy Field	lshifted (Å)	lo (Å)	Dl (Å)	V (km/sec)
1. Ursa Major II	k	3934
s/n =	m =	M = -22	d (Mpc) =
Ursa Major II	k	3934
s/n =	m =	M = -22	d (Mpc) =
2. Ursa Major I	k	3934
s/n =	m =	M = -22	d (Mpc) =
Ursa Major I	k	3934
s/n =	m =	M = -22	d (Mpc) =
3. Coma Berenices	k	3934
s/n =	m =	M = -22	d (Mpc) =
Coma Berenices	k	3934
s/n =	m =	M = -22	d (Mpc) =
4. Bootes	k	3934
s/n =	m =	M = -22	d (Mpc) =
Bootes	k	3934
s/n =	m =	M = -22	d (Mpc) =
5. Corona Borealis	k	3934
s/n =	m =	M = -22	d (Mpc) =
Corona Borealis	k	3934
s/n =	m =	M = -22	d (Mpc) =

Procedure (continued): 8) Draw the best straight line through the data points on the graph making sure that the line passes through the origin; 9) Calculate the Hubble constant from the slope of the line and record your answer here:

Hubble Constant = _________ km/sec/Mpc

10) Calculate the age of the universe in billions of years from 1/H using conversion factors (1 billion years = 3.15 x 10¹⁶ seconds and 1 Megaparsec = 3.086 x 10¹⁹ kilometers) and record your answer here

Age of Universe = _________ billion years