Venus Transit

Lou Mayo

NASA Sun Earth Connection Education Forum

June 8, 2004

0.4AU 0.7AU 1AU 1.5AU

5AU 10AU 20AU 30AU

Comparison Solar System Bodies-185C/370C 600C -70C /50C -161C/0C

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

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 HistoryCopernican 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 sizeCynthiae 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 HistorySize 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.

• Captain James Cook et al., observed the 1769 transit from Tahiti.

Local Time D ( % of Sun's Diameter)3.15 pm 48.063.35 pm 45.003.45 pm 43.33

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

T = Synodic Period = 583.92 days8 Earth years ~ 2922 days, 5 Venus synodic periods ~ 2920 days.

Aristarchus of Samos (c.310 - 230 BC)Early Estimate of the Astronomical Unit

Measured = 87deg. Therefor: ES/EM = 1 / cos (87 deg) ~ 20and…’

Another Way….

Therefor, we need the R, radius of the earth...

Eratosthenes of Cyrene (c276 - 195 BC)

Syene

Alexandria

7.2 deg =

Circumference = C = 50 x 5000 = 250,000 stades ~ 25,000 milesC = 2 R,… so …. R = C / 2 miles

R

The actual radius of the Earth is 3,963.21 miles

…. And we need the

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.

Details of 2004 Visibility

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 stateof science when the next transit season arrives God only knows."