Farewell, my lovely

It’s almost over. Venus has been dazzling and delighting us for months now, the best apparition of the evening star since 2004. It’s still amazingly bright in the northwest during the first couple of hours after sunset. It’s hard to believe that this will now change so rapidly.

As darkness falls each evening during the next few weeks, Venus will get lower and lower. In just three weeks it will be gone for keeps. But before it vanishes, it can show us some amazing things about our solar system.

We all know that the sun and the Moon set in the west. We also know that the point of sunset and moonset shifts position. The sun always sets at its rightmost spot on the horizon — in the west northwest — on June 21. It can never set further to the right than that, not even in a billion years. Meanwhile, other solar system bodies have slants or tilts to their orbits, and on rare occasions can set further north than the sun ever gets.

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That’s what Venus is doing now and will continue to do until it vanishes in late May. Look out your west or north facing window at 9 or 10 p.m. There’s unmistakably brilliant Venus. Notice how far to the right it appears. It sets almost exactly in the northwest, at a place the sun never reaches. It’s where even the moon only manages to occupy during a single year of its 18.61-year orbital cycle, a position it last exhibited in 2006 and won’t occupy again until 2024.

This is happening because Venus is not only passing through the most northerly part of the zodiac, but is also several degrees north of  its average position, displaying the full 3.4-degree tilt to its orbit.

I don’t want this to get too technical. The main points are: enjoy the evening star because we’re about to lose it, and the sky will be much lonelier once it’s gone. And secondly, enjoy the rare sight of a brilliant solar system object in a very unusual place. It’s one of the odd times when you can see a planet out your north-facing window.

One more thing. Only now does Venus look interesting through binoculars or a small telescope. It displays a crescent shape that grows narrower yet larger with each passing evening. Strange lunatic stuff, best observed during twilight rather than a black background. It’s as though our sister planet is prepping us for its oddest behavior of all before vanishing when it crosses the face of the sun on June 5.

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