Astronomy Essentials

Venus phases: Late 2019 and early ’20

Venus in the Evening Sky from 2019 to 2020 from Larry Koehn on Vimeo.

EarthSky friend Larry Koehn of the great website created this animation. The video tracks a telescopic view of Venus, from when it became visible in our evening sky around September-October 2019, all the way to May 2020. All animations are set for exactly 30 minutes after sunset. You can see some other planets coming and going in the evening sky, too. Thank you, Larry!

Did you know that Venus shows phases? Through a telescope, it can look like a tiny, featureless waning or waxing moon.

At this writing (late February 2020), Venus is in a waning gibbous phases. In other words, telescopic observers are seeing it as more than half lighted, but less than full.

Smaller to larger crescents with the largest very thin and the last picture a circle with a dark middle.
Here’s the planet Venus seen through a telescope beginning in late February 2004. As the months passed, the planet waned in phase, because we saw less of its day side. Meanwhile, Venus appeared bigger and bigger from Earth, because it was traveling closer to us in its smaller, faster orbit. Finally, in August 2004, Venus passed between the Earth and sun. At that point, it exhibited a “new” phase with its dayside turned entirely away from us, and a rim of light seen shining around the planet through its thick atmosphere. Image via Statis Kalyvas/ European Southern Observatory/ Wikimedia Commons.

Why does the phase of Venus change? It’s because this world orbits the sun on an orbit inside that of Earth’s. As a result, we sometimes see a fully lighted Venus: all of its day side. And we sometimes see a gibbous or crescent Venus: just a sliver of its dayside.

Venus first entered the evening sky at full phase on August 14, 2019, a couple of months before people began spotting it. Then it was far across the solar system from us, and – if you could see it at all in the sun’s glare – you were seeing nearly all of its dayside.

Since then – as Venus has moved along in its smaller, faster orbit around the sun, preparing to pass between the Earth and sun in June of 2020 – Venus has been waning as seen from Earth. Around late March 2020, Venus will have passed its half-illuminated last quarter phase, and start to show itself as a waning crescent in our sky. Venus will shine most brightly as the evening “star” in late April/early May 2020. Paradoxically, it’ll be a crescent Venus shining so brightly; the brightness will stem from the planet’s nearness to Earth, as, by that time, Venus will be hot on Earth’s heels in orbit. Around late May and early June 2020, people with good vision might be able to see the crescent Venus with the eye alone.

Venus will pass between us and the sun, leaving our evening sky on June 3, 2020. Then the planet will be at the new phase, with its sunlit side turned entirely away from us. It’ll be a waxing crescent Venus that reappears in the east before dawn a few days later.

Chart of curved track in the sky with the planet increasing in size and changing phase along it.
View larger. | Venus officially entered the evening sky on August 14, 2019, and will officially leave it on June 3, 2020, the day upon which it’ll pass between us and the sun. This diagram shows the phase of Venus – visible through small telescopes – throughout this evening apparition. Chart via Guy Ottewell’s blog.

Bottom line: Video animation of the track of Venus (and other planets) from the time Venus became easily visible in the evening sky around September-October 2019 to May 2020.

Read more: EarthSky’s guide to the bright planets

Via Larry Koehn

Via Vimeo

February 29, 2020
Astronomy Essentials

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