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Distances

Distances. Transit of Venus. A transit occurs when one object in space passes in front of another. Venus transits the Sun twice each century 2004 and 2012 2117 and 2123. NASA – Solar Dynamics Observatory. Halley’s Method.

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Distances

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  1. Distances

  2. Transit of Venus • A transit occurs when one object in space passes in front of another. • Venus transits the Sun twice each century • 2004 and 2012 • 2117 and 2123 NASA – Solar Dynamics Observatory

  3. Halley’s Method • The transit of Venus was used to measure the parallax distance to the Sun. • The time difference is equivalent to an angular change. • Defines the AU Vermeer, Duckysmokton, Ilia

  4. Sources of Parallax • Geocentric parallax uses the earth as a base. • Take a photo two times in one night. • Heliocentric parallax uses the sun as a base. • Take a photo at two different seasons.

  5. Shifting Stars • The orbit of the earth is used as the base. • Near stars appear to move more than far stars. site A site B

  6. Parsec • An arc-minute is 1/60 of a degree. • A playing card on edge at arms length • An arc-second is 1/60 of an arc-minute. • A human hair thickness at 10 meters • Distance is related to the parallax angle. • one arc-second gives about 3.3 ly. • This parallax-second is defined as one parsec (pc).

  7. Stellar Parallax • A telescope photo of the stars will show the shift. • Arcturus 11.3 pc ESA - Hipparcos

  8. The ESA operated Hipparcos from 1989-1993. Parallax measurement 0.001 arc-second accuracy 118,200 stars Hipparcos

  9. The ESA launched Gaia in December 2013. 24 micro-arc-second accuracy Human hair at 1000 km The goal is to catalog 109 stars. Gaia

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