Most scientists agree that the universe began some 14 billion years ago in an event known as the Big Bang. Though the Big Bang suggests a colossal explosion, the universe didn’t explode into anything. Space itself, was created in this explosive expansion. Since the Big Bang, the universe has continued to expand.

The “Big Bang” is a scientific theory about the origin and evolution of the universe. A scientific theory is more than “just a theory”. Scientific theories predict new phenomena, and so can be tested.

How do we know?

Q. How do we know that the universe is expanding?

A. Almost very galaxy we see is moving away from us. We measure this with the Doppler shift.

Q. How do we know the expansion was caused by the Big Bang?

A. Galaxies further away are moving away faster in proportion to their distance. Hence, they all started from the same place at the same time.

Q. How do we know that the faster-moving galaxies are farther away than the slow ones?

A. The faster ones appear fainter and smaller in proportion to their speed.

Edwin Hubble first noticed this relationship before 1920.

Using this line of evidence, and the spiral galaxies listed below, you can measure the age of the universe. With only 10 galaxies, your answer won't be as accurate as the value obtained by current cosmic researchers. But you'll be in the ballpark, and much closer than Edwin Hubble! What you need to know:

The galaxy images are available as FITS data files or as Jpegs. You will need software like Hands-On Universe to open the FITS files. If you don't have the right software that's ok--you can use the printed images of the galaxies and spectra. But, if you have HOU at your disposal, the angular size of the galaxies can be determined in this way.

Power Point Presentation

In this presentation, I used just four galaxies - I have used this presentation with groups as large as 200 students! I hand out jpg images of the four galaxies and their spectra. The students order the galaxies by size, then using the assumption that they are all the same instrinsic size, we calculate their distance, using the spectra.

Excel worksheet

If you download this worksheet into the same location as the Powerpoint, you can access the numbers during the presentation.

Conversion numbers used in this presentation:

parsec = 3.259 light years

light year = 9.461 x 10^12 km

parsec = 3.1 x 10^13 km

seconds to years = divide by 31536000 (60x60x24x365)

1km/sec = 3.3 x 10^-6 lightyears/year

Here are the files you need to do this activity: