No, the image at top is not the moon! That’s the planet Venus as seen through the telescope at its greatest evening elongation on November 1, 2013. Image credit: US Naval Observatory Greatest elongation means that Venus is now at its greatest apparent distance from the sun, as seen on the dome of Earth’s sky. It means this is a good time to see Venus! Look west after sunset. Venus is the brightest “star” up there.
Today, Venus’ greatest evening elongation places the planet 47o east of the setting sun.
Venus, the second planet outward from the sun, circles the sun inside of Earth’s orbit. Therefore, Venus can never be opposite the sun in Earth’s sky. In fact, Venus can never get as far as 90o from the sun, as the moon does at its first quarter and last quarter phases.
For the Northern Hemisphere, this is not a particularly favorable elongation of the sky’s brightest planet, with Venus setting about 2.5 hours after the sun at mid-northern latitudes. In the Southern Hemisphere, in stark contrast, Venus sets over 4 hours after the sun at mid-southern latitudes.
There are two reasons why Venus sets later in the Southern Hemisphere. The tilt of the ecliptic – the pathway of the planets – makes a shallow angle with the horizon as the sun sets at northerly latitudes, but a steep angle at sundown at southerly latitudes. Also, the planet Venus lurks to the south of the ecliptic at present, which causes the planet to set even later after sunset in the Southern Hemisphere but sooner after the sun in the Northern Hemisphere.
At greatest elongation, Venus is always pretty much half-lit in sunshine and half-engulfed in its own shadow (like the moon at first or last quarter phase). If you have a telescope, set it up and take a look at Venus as soon as it pops out after sunset. It’s best to view Venus at early dusk, before the glare of this brilliant world becomes too overwhelming. If you can find Venus in the daytime sky, that’s better yet.
Five weeks after Venus’ greatest evening elongation, this planet will stage its greatest brilliancy as the evening “star.” At this juncture, Venus’ disk will be about 25% illuminated in sunshine and 75% covered over in planet’s own shadow. Then five weeks after displaying its greatest brilliancy (or ten weeks after reaching its greatest evening elongation), Venus will swing between the Earth and sun. Venus is said to be at inferior conjunction at this juncture, as shown on the illustration below.
Bird’s-eye view from the northern side of solar system plane
At inferior conjunction, Venus lies between the Earth and sun, just like the moon at new moon. The “new” Venus – unlike the new moon – transitions from the evening to morning sky at inferior conjunction. The new moon goes in the opposite direction, passing from the morning to evening sky.
Bottom line: Venus – the third brightest celestial object after the sun and moon – is now reaching a milestone as the evening “star,” adorning the western twilight and evening sky after sunset. Watch the dazzling planet Venus on the evening of November 1, 2013, as it reaches its greatest elongation from the sun.