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Wednesday, April 25, 2012

Venus brightest in evening sky late April and early May


This post was pilfered from EarthSky.org


The planet Venus reaches its “greatest illuminated extent” at the end of April 2012. Greatest illuminated extent means Venus’ lit side is covering a maximum area of sky, so 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.

Look outside shortly after sunset, and you can’t miss Venus. It’s an eerie light in the western sky. Venus’ brightness will surprise you if you’ve never noticed it before. It’s so bright that, around now, many people will report Venus as a UFO.

But this is no exotic or unidentified object. It’s simply our neighboring planet in orbit around the sun. On March 27, Venus passed a hallmark of its year when it appeared at its greatest elongation from the setting sun on our sky’s dome. Right now, Venus is approaching its greatest brilliancy in the western twilight sky. Venus’ illuminated portion covers the most sky on April 30 at 8 Universal Time.

In the coming week, Venus will shine at its maximum brightness, at -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.

Phases of Venus Diagram

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?

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.

Last transit of Venus in 21st century will happen in June 2012

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.

Late April and early May present Venus’ maximum brilliance! Watch for Venus as a dazzling light in the west after sunset.

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