If you’ve been watching the western sky after sunset, you’ve seen the planet Venus. It looks eerily bright now – brightest in the evening sky for all of 2012! If you haven’t seen it yet, look outside shortly after sunset, and you can’t miss this planet. It’s an eerie light in the western sky. Venus’ brightness will surprise you if you’ve never noticed it before.
Astronomers call this a greatest illuminated extent for Venus. The planet will reach greatest illuminated extent at the end of April 2012. What does it mean? Think of seeing Venus not just with your eye, but with a telescope. Through a telescope, you can see the round disk of Venus – except that right now Venus’ disk does not appear fully round and illuminated. Right now, Venus appears as a crescent, like a tiny crescent moon. And yet that crescent Venus looms large, as your telescope would show you, if you peered through one. Venus’ lighted portion – the illuminated crescent – is at its largest in our sky: its greatest illuminated extent. Venus’ illuminated portion covers the most sky on April 30 at 8 Universal Time.
It’s at or near this juncture that Venus shines at its greatest brilliancy in our sky. Are you seeing a very bright object low in the western sky after sunset? That’s Venus, appearing at its very brightest as the “evening star” throughout late April and early May. Venus is so bright now that many will report it as a UFO.
In the coming week, Venus will shine at its maximum brightness of -4.6 magnitude. How bright is that? That’s about 70 times brighter than Arcturus, one of the brightest stars in all the heavens – now in the east part of the sky at nightfall. If you’re in the Northern Hemisphere – where Venus stays up for a few hours after nightfall – it might be possible to notice shadows cast by Venus. You’ll have your best chance to see shadows cast by Venus once the moon leaves the evening sky, starting the second week of May.
So Venus is about at its brightest in the evening sky. Yet – in what seems like a paradox – a telescope would reveal Venus now as a waning crescent. It looks like a tiny, featureless crescent moon. Because the orbit of Venus lies inside of Earth’s orbit, Venus goes through phases, much like our moon. Surprisingly, Venus’ disk appears only 28% illuminated right now, as seen from Earth. Venus appears at its brightest when it’s about one-quarter illuminated. How can it be shining at or near peak brightness when we’re seeing only a portion of its lighted hemisphere?
Phases of Venus Diagram
The answer is that – when Venus appears full as seen from Earth – it’s always much farther away, on the far side of the sun from us. That’s the only place it can be in order for its fully lighted disk to be facing our way. Full Venus = more distant Venus = fainter Venus overall.
Now Venus is on the same side of the sun as Earth. It will go between us and the sun on June 5-6, 2012. So a portion of the day side of Venus is turned away from us, and we see a crescent Venus. Yet Venus on the same side of the sun as us, and therefore closer. A telescope would reveal the crescent, but it would also show the crescent as very large. Thus Venus is brightest now.
By the way, in the weeks ahead, Venus will be coming closer still to Earth, but it will be showing us less and less of its lighted hemisphere (day side) as it prepares to pass between us and the sun.
Bottom line: Late April and early May present Venus’ maximum brilliance! Watch for Venus as a dazzling light in the west after sunset. Many will report Venus as a UFO around this time. But you’ll know better.