A transit of Venus across the face of the Sun took place in 2012 when the planet was passing through the descending node in its orbit at the same time it reached inferior conjunction. Currently, inferior conjunction can only coincide with the descending node during June. It is also possible for a transit to take place if Venus is passing through the ascending node of its orbit at inferior conjunction, and this can only take happen during December. The descending node is near the aphelion of Venus' orbit, so Venus appears slightly larger during a descending node transit than it does during an ascending node transit; in other words, Venus is a little bit closer to us in June than it is in December. The difference in apparent size is small because the planet's orbit is nearly circular. In contrast, the orbit of Mercury is eccentric, and the size of Mercury varies considerably between an ascending node transit of Mercury, and a decending node transit of Mercury.
Transits of Venus typically occur in pairs that are 8 years apart. The 2012 transit was preceeded by a transit of Venus in 2004. The second transit in a pair occurs 2.4 days earlier than the previous transit. Thus, the 2004 transit occurred on June 8, 2004, and the 2012 transit occurred on June 5. Since the transit times differ by 2.4 days, the 2004 transit was only visible from the other side of the world, while the 2012 transit was visible from the United States. A pair of descending node transits are followed by a pair of ascending node transits 105-1/2 years later. Thus, the next transit of Venus will take place on December 11, 2117, when Venus reaches inferior conjunction while it is also at the ascending node of its orbit. A pair of ascending node transits are followed 122-1/2 years later by a pair of descending node transits.
This image was taken near the begining of the transit from my backyard in Scottsdale, Arizona, using a Canon EOS Digital Rebel SLR camera on a Takahashi FCT-150 refractor with a Thousand Oaks Optical Type 2+ solar filter.
The Sun & Venus
June 5, 2012
Image by Sid Leach
Scottsdale, Arizona
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