Conjunction Function? Looking Pretty!

Have you noticed bright lights in the western sky, soon after sunset? Maybe you heard something somewhere about a planetary alignment. Maybe the Weekly World News you glanced at (first looking around to make sure nobody was watching) in the checkout line said something about the alignment, Bat Boy, Mel Gibson and the Mayan Calendar Apocalypse. Well, there are some pretty goings on in the western sky, at least that much is true. Here’s the skinny:

The planets Venus and Jupiter, easily noticeable since they are two of the brightest “stars” in the night sky, are approaching each other, or rather, they appear to be approaching each other from our vantage point, and they’ll appear to draw nearer to one another until March 14th, when we’ll all start to get really suspicious that something is going on between those two.

Here’s a representation of the relative positions of the planets on February 24th. This model is based on the Copernican model, which places the sun at the center of the solar system (and placed Galileo in hot water with the Church). Believers in other cosmological models, please stop reading and whatever you do, don’t look at the image below, it’s obscene. For everyone else, rationally note that the following image is not remotely to scale. The planets are proportionally correct in relation to each other, in other words, Mercury is smaller than Venus, and Mars is smaller than Earth, and Jupiter (and the Sun) are bigger than all of them, but that’s as much as you can say. The orbits are condensed and not proportional, except that Jupiter is much farther out than the inner planets. That’s why they are inner planets and it is the first of the outer planets! Most importantly, the planets are positionally more or less correct for March 2012 so we can at least see a rough approximation of the geometry at work here. Gosh, this almost took longer to introduce than it did to draw in Illustrator.

If you draw a triangle between Earth, Jupiter and Venus and you get an idea of how we perceive the conjunction. As Jupiter moves (in this image clockwise) in its orbit, the angle Jupiter-Earth-Venus narrows. Venus is moving clockwise as well, but from earth it appears to be receding, whereas Jupiter appears to be dropping towards the Sun. Let’s add an observer to the surface of the earth, in a position just after sunset.

You get the idea. The angle Jupiter-Bicycle Astronomer-Venus is much smaller than, say, Mars-Bicycle Astronomer-Jupiter. Indeed, Mars and Jupiter are on opposite sides of the evening sky. Venus and Jupiter are “setting” in the West, appearing to follow the Sun, while over the Bicycle Astronomer’s shoulder, Mars is “rising” in the East, the brightest reddish “star” in that direction. Here is the Bicycle Astronomer up close:

As I wrote above, the angular separation of the nightmare greenhouse gas planet of Venus and truly giant gas giant Jupiter will appear to shrink until March 14th. Ten days later, a thin waxing crescent moon will appear near the horizon below them, and our couple will, well, get a little more complicated. Mark your calendars and wander outside when you’re finished with your supper, and look west. The conjunction is pretty much an optical trick caused by the geometry of the clockwork solar system, but it’s still really pretty. It shouldn’t cause the end of the world, either.

Here’s a nicely-made video by Nasa about the conjunction, which also explores why exactly it might appear so strikingly beautiful to us, a theme I’ll pick up in the next post.


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