16 August 2007
Venus’s crescent appears to swivel as its inferior conjunction progresses and the planet moves past the Sun
THE BRILLIANT PLANET Venus lines up with the Sun on 15 August, when it reaches a position in its orbit known as inferior conjunction. This is when it’s on the earthward side of its orbit, between us and
the Sun. In contrast, superior conjunction occurs when it lines up with the Sun on the most distant part of its orbit.
The line-up is not precise and Venus will pass south of the Sun’s disc. This time round
the distance is respectable, with the star and planet being separated by around 8º. This means that with care, it’s possible to image the crescent of Venus as it passes through inferior conjunction. The line from the centre of the planet’s disc, through the thickest part of the crescent, always points to the Sun. Consequently it appears to swivel as Venus passes into the morning sky.
The crescent is very thin and great care is required to catch it with a camera. We covered how to locate Venus by using the Sun in the Sky Guide last month – you can read an abridged version of this article online at www. skyatnightmagazine.com/ feature/how-guide/how-findimage-venus. This is not a safe visual target so it’s cameras only we’re afraid.