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How Far?

How Far?. Measuring Distance in the Universe. How?. Gian Domenico Cassini, in 1672, used a technique called parallax to measure the distance to Mars. . Cassini figured it out!. The Sun is about 93 million miles from

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How Far?

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  1. 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

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