1. Measuring Distance in the Universe
How Far?
Measuring Distance in the Universe

2. How?
Gian Domenico Cassini, in 1672, used a technique called parallax to measure the distance to Mars.

3. Cassini figured it out! The Sun is about 93 million miles from
Earth. As Earth and Mars never come closer than 35 million miles to each other.
Saturn, the most distant planet known when Cassini was alive, is around 900 million miles away.

4. How?
Parallax!

5. What is Parallax? Try this out: Hold 1 finger out at arm’s length
Close one eye, and then the other
Notice how your finger “jumps?

6. Measuring Stars
Stars are billions of light years away – winking won’t help
Our orbit is 186 million miles wide (93 million + 93 million)
Star A and B are the same star, as they appear 6 months apart

7. How to: The parallax angle p is illustrated in the above figure.
We can determine they adjacent (d) using trigonometry.

8. Trigonometry
Our adjacent line (d in the prior picture) is the distance from Earth’s Orbit (BC) to the star (A)
Adjacent length= opposite length tangent angle A

9. Trigonometry
Measure the angle of the star to our central point of orbit
Simple calculation
Even the Hubble Telescope limited to 1000 LY
Earth’s Orbit

10. Parsec
The method of parallax gives rise to a natural distance unit that astronomers call the parsec.
defined as the distance at which a star would have a parallax angle p equal to one second of arc.
using trigonometry distance equal to 206,265 astronomical units or 3.26 LY
AU is the average distance of Earth to Sun

11. Further away? The universe is expanding
Galaxies furthest away are moving away faster than galaxies closer to us
We can us Doppler Effect

12. Visible Spectrum

13. Doppler
Doppler

14. What is Red Shift? As light moves away, the waves stretch out
Longer waves are shifted towards the red
As light moves towards us, the waves condense
Shorter waves are shifted towards the blue

15. Spectral Signature Each element has a unique spectral signature
Two elements combine