Gibbous Venus

Is it poor form that I’m not a huge fan of Venus as an object to watch in an evening? After all, its clouds prevent you from seeing any features on the planet’s surface, making it a less-than-totally-exciting sight.

However, if you keep an eye on them over time, all planets do strange things, like change brightness or stop and go backwards every now and again.

Venus is currently (January 2020) approaching its “maximum elongation” – that is, the furthest it gets away from the sun. That’s actually going to be a bit later this year, on 25 March.

This diagram shows where Venus is going to be in January and again in April (and yes, I know I mislabeled it 2019 rather than 2020), in relation to the Earth. About now, Venus is trailing the Earth, meaning it’s an evening object, and is nearly at its greatest distance away. It’s also showing most of its lit face to us. The word astronomers use is “gibbous”.

Venus looking nearly round and pretty small isn’t a great sight. It’s bright, and way high though.

But Venus is closer to the Sun than we are, so it orbits faster. By April (if you look at the diagram again) it will nearly have caught us, and so it’ll be much closer – and therefore larger. But the cooler thing is that it’ll also change shape, moving from gibbous to crescent.

A large crescent (well, large for Venus) is way cooler than a small blob, I have to say.

Of course, because it’s catching us up, it’ll also appear closer to the Sun, and will disappear into the evening Sun’s glare, before passing the Sun on the 4th of June. After that, it’ll appear as a morning object and do pretty much the whole thing backwards.

So planets might be cool on a single evening, but over time they get way more interesting.

For those who are interested, the way Venus’ phases change over time was the final nail in the coffin of the Ptolemaic map of the solar system. Galileo used his telescope to study Venus over time and figured that it just couldn’t be orbiting the Earth, no matter where the Sun was shining from.