Venus Transit by liaoqinmei

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									Venus Transit
      June 8, 2004




        Lou Mayo
 NASA Sun Earth Connection
     Education Forum
    Comparison Solar System Bodies
-185C/370C 600C     -70C /50C    -161C/0C




    0.4AU   0.7AU     1AU         1.5AU

  -153C             -180C       -210C       -210C




   5AU                10AU      20AU        30AU
                             Venus
Venus weak magnetic field is an
induced field from direct interaction
between the solar wind and the
ionosphere.

Equator to pole temperatures vary by
only a couple of degrees

Thick CO2 and H2SO4 atmosphere
obscures the surface in visible light

The solar wind and high atmospheric
temperatures contributed to the almost
complete loss of any water.

Size and Mass ~ Earth’s

Magellan Radar Images show evidence
for vulcanism
           Venus’ Role in History
           Copernican System: 1, Ptolemaic System: 0

• Earliest records of observation
  date back to Babalonians ~3000
  B.C.
• First telescopic observations -
  Galileo, 1610.
    – Venus had a cycle which could
      not be explained by its rotation
      around the earth
    – Venus exhibited phases
    – Venus changed apparent size
                                          Cynthiae figuras aemulatur mater amorum.
                                          Translated: "the mother of love [Venus]
                                          emulates the figures of Cynthia [the Moon]."


                                         • 1761 Transit was used to measure
                                           longitude before there were accurate
                                           clocks
             Venus’ Role in History
                Size of the Solar System - Revealed!
• Kepler predicted the transit of
  December 1631 (though not
  observed!) and 120 year cycle.
• Jeremiah Horrocks (born
  c.1619) predict that a further
  transit of Venus would occur
  on 4th December 1639
• 1761 transit observations partly
  successful in determining value
  of A.U. Russian astronomer
  Mikhail V. Lomonosov,
  suggests Venus has an
  atmosphere.                        Local Time   D ( % of Sun's Diameter)
                                     3.15 pm      48.06
• Captain James Cook et al.,         3.35 pm      45.00
  observed the 1769 transit from     3.45 pm      43.33
  Tahiti.
1882 Transit
  (USNO)
      TRANSIT DATES
         •December 1631
         •December 1639
•June 1761
•June 1769
         •December 1874
         •December 1882
•June 2004
•June 2012
         •December 2117
         •December 2125
It’s All in the Geometry
DT = Synodic Period = 583.92 days
8 Earth years ~ 2922 days, 5 Venus synodic periods ~ 2920 days.
  Aristarchus of Samos (c.310 - 230 BC)
          Early Estimate of the Astronomical Unit




                                             d




Measured a = 87deg. Therefor: ES/EM = 1 / cos (87 deg) ~ 20
and…d ~ 3’
       Another Way….




Therefor, we need the R, radius of the earth...
  Eratosthenes of Cyrene (c276 - 195 BC)
The actual radius of the           Alexandria
Earth is 3,963.21 miles

                           7.2 deg =




                                   R

                                                Syene




Circumference = C = 50 x 5000 = 250,000 stades ~ 25,000 miles
C = 2 p R,… so …. R = C / 2 p = 25,000 / 6.26 = 3,994 miles
…. And we need the a
       Details of 2004 Visibility
External Ingress: 05:13:25 UT

Internal Ingress: 05:32:52 UT

Maximum: 08:19:40 UT

Internal Egress: 11:06:30 UT

External Egress: 11:25:56 UT

Angular speed across disk of sun about 0.4 degrees in 6 hours
= 0.07 degrees/hour.

Diameter of Venus disk = 58.6 arc seconds.
Ref: http://www.chocky.demon.co.uk/oas/venus.html
Application to Exo Planet Studies




                   HD 209458 (mv = +7.7) in Pegasus
1882, the date of the last Venus transit, quote by
William Harkness of the U.S. Naval Observatory
(from Sky and Telescope, Feb. 1995):

"There will be no other [transit of Venus] till the twenty-
first century of our era has dawned upon the earth, and
the June flowers are blooming in 2004. When the last
transit occurred the intellectual world was awakening
from the slumber of ages, and that wondrous scientific
activity which has led to our present advanced
knowledge was just beginning. What will be the state
of science when the next transit season arrives God only
knows."

								
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