THE EVENING STAR
Venus circles the Sun once every 225 days. But because Earth is also moving, it takes 584 days before Venus re-appears in the same part of our sky. This makes the typical Venus apparition a far more leisurely business than Mercury's frantic scurry.
It begins when Venus emerges from the Sun's glow, low in the evening twilight. At this point, it looks small (about 10 arcseconds across) and round in phase.
Each night, the planet climbs higher, moving farther from the Sun. At greatest eastern elongation, it stands highest above the western horizon. It is in half-lit phase, but it has grown to about 25 arcseconds. Now at magnitude —4.5, the planet will be brighter than anything in the sky except the Sun or Moon. Although it does not move visibly, Venus resembles an airplane with landing lights on, and has caused many a UFO report.
After greatest elongation, Venus loses altitude but grows even brighter as it approaches Earth. The point of greatest brilliancy occurs about 4 weeks before inferior conjunction.
Venus is then bright enough to cast a shadow. In a. dark location, hold a sheet of white paper facing Venus. Let your eyes dark-adapt, then move your hand just in front of the paper. The shadow will be sharp-edged compared to shadows cast by the Sun or Moon. This is because Venus is a point-source of light, nither than a broad disk.
A week before inferior conjunction, Venus is in crescent phase, but has grown to nearly
60 arcseconds across—just within the resolving power of human eyesight. Not every-one's vision is acute enough to see the crescent, however, and binoculars can help.
At inferior conjunction, Venus overtakes Earth, leaves the evening sky, and shifts into the morning. Thereafter, it rises before the Sun, repeating the stages of its evening performance, but in reverse order.
Superior conjunction, when
Venus lies on the other side of the Sun from us, marks the close of one apparition—and the start of the next.