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Astro Bob: Full-moon aurora plus Venus returns as the 'Evening Star'

Aurora may return this weekend (March 27-29), the same time Venus transitions from Morning Star to Evening Star.

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A small section of a rayed arc in the March 13th aurora briefly brightens into a narrow beam. (Bob King)
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March has certainly been a busy month for the northern lights. I recorded auroras on five nights: March 2, 5, 12, 13 and 19th. Guess what? They may return for an encore this weekend. Minor geomagnetic storms are predicted for Saturday through Monday nights, March 27-29. Best viewing times will be later in the evening after about 10 p.m.

There's a rub, though. The moon will be full at the same time, making it difficult to see any display unless it becomes brighter than expected. On these moonlit nights, ardent aurora seeker often take photos anyway in hopes of capturing the the green glow photographically even if it's barely visible to the eye.

If the thought of missing the green makes you blue, take heart. Spring's a busy time for auroras with more activity predicted for April 9 and April 15-16 when the moon will be absent. If you haven't seen the northern lights yet, hang in there!

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Venus and geese are reflected in a pond during evening twilight in March 2010. (Bob King)

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Amateur astronomy is all about patience. You'd think after almost 60 years of looking at the stars and planets I'd be the most patient human being on Earth. Nope, I get antsy like everyone else. In fact, I'm itching to see Venus again. It's been missing in action the past month, hiding in the solar glare. On March 26, the radiant goddess of beauty will be in superior conjunction with the sun and then make a slow return to the evening sky.

Venus SOHO March 25.jpg
The Solar and Heliospheric Observatory (SOHO) took this photo of Venus on March 25 using a special mask to block the sun's glare. The planet is nearly lined up below the sun in conjunction, which occurs on March 26. Refer to the diagram below to see where Venus is in its orbit at this time. (NASA / ESA)

Venus has two types of conjunctions or close alignments with the sun as seen from Earth. When it's in superior conjunction, the planet lies up on the opposite or far side of the sun. From our perspective, sunlight illuminates the entire nearside of the planet and it looks like a tiny full moon when viewed through a telescope. This phase is difficult to see because you're looking almost straight at the sun.

A little more than 9 months later, Venus swings almost directly between the Earth and the sun at inferior conjunction. Again, from our perspective, it lines up with our star, and the planet disappears from view in the solar glare. Through binoculars or a small telescope it looks like a skinny crescent just before and after conjunction because the angle Venus makes with the sun is so narrow, the sun only illuminates its curved edge.

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Venus reaches superior conjunction with the sun this week, when it makes the transition from the morning to the evening sky (left side of diagram). As its apparent distance from the sun increases, its phase slowly changes from full to half. On Oct. 29, the planet will appear farthest from the sun at dusk and then line up with it again at inferior conjunction next January. After that, it moves to the morning sky. (Bob King)

Immediately after superior conjunction on Friday (March 26) Venus transitions into the evening sky. Yay! Whoa, slow down. You and I won't see it until the start of May low in the northwestern sky about a half-hour after sunset. Why the wait? Venus lies on the opposite side of the sun from the Earth, so it's really far away from us. A distant planet appears to move more slowly than a near one the same way an airborne jet crawls across the sky compared to watching the same jet up close taking off from the runway.

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That's why Venus takes its sweet time moving far enough away from the sun so we can see it finally at dusk. Watch it climb up slowly from the horizon during the summer months, reaching its greatest apparent distance from the sun in October. During this time the planet's phase will morph from full to gibbous to half as the angle the planet makes to the sun and the Earth changes as it speeds around its orbit.

Inferior conjunction occurs in January 2022, when Venus passes to the right (west) of the sun and returns to the morning sky. Unlike the changeover from morning to evening, this transition happens quickly because the planet is almost 6 1/2 times closer to us than at superior conjunction. Venus swiftly departs the solar glare and reappears at dawn in a matter of weeks.

All the planets have their own individual cycles. Getting to know them is one of the simply joys of skygazing.

"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob .

"Astro" Bob King is a freelance writer and retired photographer for the Duluth News Tribune. You can reach him at nightsky55@gmail.com.
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