Venus actually has two inferior conjunctions in March of 2009, based on two different definitions of "conjunction." On March 25 UT (March 24 Pacific
Time) the Right Ascension of Venus is equal to the Right Ascension of the Sun. On that date, were you to look down on the Solar System from directly
above the Earth's North Pole, Venus would lie on the straight line connecting the Earth and Sun. That is one definition of conjunction, a "conjunction in
Another definition of conjunction is the point where the angular displacement between the two bodies, Venus and the Sun, are at the minimum. Since
the Earth's axis of rotation lies at an angle relative to the axis of its orbit around the sun, Venus appears (as seen from Earth) to move in Declination as
well as in Right Ascension each day. So Venus may approach closer to the Sun (by moving in Dec) than the point at which it shares the same line of
Right Ascension (RA) as the Sun. (See graphic aid below <G>)
Usually the two types of conjunction occur within a few hours of each other but are not simultaneous.
The apparent angle (as viewed from the Earth, looking towards the Sun) between the axis of the Earth's rotation and the axis of the Earth's orbit
superimpose at the Solstices and have their greatest difference at the Equinox. Since this conjunction of Venus occurs near the Earth's Equinox where
the angle between those two axes is greatest, several days (rather than the typical few hours) separate the two conjunctions. The angular displacement
of Venus from the Sun was about 9 1/2 degrees on March 25 UT, the time of the conjunction in right ascension. The displacement continued to
decrease over the next 3 days diminishing to about 8 degrees on March 28 UT (March 27 Pacific). This year the angular displacement at conjunction
was particularly large so Venus could be seen from the northern hemisphere all the way through conjunction.
In the sequence above the apparent size of Venus becomes larger as its distance from Earth decreases from 0.32 AU March 24 to 0.28 AU March 27
(Pacific Time). The visibly lit fraction of the planet decreases and the angle of illumination changes as Venus swings just north of the sun.
Because of its small angular displacement from the sun, Venus was at extremely low altitude at sunset. This would have resulted in very poor seeing
were Venus imaged after sunset. So the images were acquired during full daylight (Noon to 5PM local standard time) at altitudes between 30 and 60
TOA150+2x Powermate (2200mm FL), Skynyx 2-1. Images captured as AVI, processed with AVI Stack, Registax and Photoshop. Best ~ 150 of each set
of 1000 frames used.
|The Conjunction(s) of Venus