Big Bang and the expanding universe
1 min 37 s. The words are spoken and shown in the picture; the player can also show them as subtitles.
For the Earth and Space Sciences Regents. Topic: Big Bang and the expanding universe, with the past questions on it.
What Dr. Mars says (the words of the video)
Why do scientists say the universe is expanding?
Distant galaxies are moving away from us.
Farther galaxies move away faster.
White light passing through a cool gas shows dark lines.
Each line sits at a fixed wavelength. Dr. Mars puts the ruler's zero under the first line.
A near galaxy shows the same lines, moved toward red.
Recorded with a telescope: longer wavelengths, a red shift.
A far galaxy shows a bigger red shift.
A bigger shift means it moves away faster.
Galaxies are moving apart: the universe is expanding.
This is evidence for the Big Bang.
A second clue: microwave radiation reaches us from every direction.
Energy left over from the hot early universe.
Check yourself! Which galaxy is the farthest from us: A, B, or C?
Think about how far each set of lines moved.
Answer: C! The biggest red shift means the farthest galaxy.
Measured from Dr. Mars's ruler, C's lines moved the most.
Dr. Mars. Free practice for the New York Earth and Space Sciences Regents.