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A while back I threatened to do a few posts on astronomy, but then inertia took over. So here goes!

First off, the Lyrid meteor shower will be at its peak tonight - the later the better as Lyra doesn't even rise in the eastern sky until about 10 PM. Expect to see about 7 meteors per hour.

On the western horizon, Venus continues to put on a dazzling show around sunset. It is absolutely unmistakable - the biggest obstacle to identifying it is assuming its an airplane or other manmade (or alien!) object. Venus is currently in the constellation Taurus the bull.

The winter's most brilliant constellation, Orion, will be setting sooner each day until it completely disappears from sight over the summer. So if you want to see it in all its glory, best head outside early! Orion is easy to distinguish because it has so many bright stars, led by Rigel (the lower right star marking Orion's left knee) and Betelgeuse (the red star on the upper left, marking Orion's right shoulder). The 3 "belt" stars in a nearly straight line are another highly distinctive feature. By contrast, Orion's head is nearly invisible on this image - Orion the Hunter wasn't particularly renowned for his intelligence. 

Since Orion is so easy to find, it can also be used to find many other objects in the 'winter' sky (ie, that portion of the sky that is in the south* near sunset during winter). Start from the upper belt star (Mintaka) and extend a line down through the lower belt star (Altnitak). Keep going about 20 degrees until you run into the brightest star in the night sky, Sirius. (Note that it may not look exceptionally bright at this time of year because it is setting and thus a little dimmed by the atmosphere. It definitely shows better in the winter.) Sirius lies in Canis Major, Orion's dog.

We now start circling clockwise to other bright stars. From Sirius, arc up and slightly to the right to Procyon in Canis Minor. This is the most boring constellation imaginable so we continue circling next to the twin stars of Gemini, Pollux on the left and slightly dimmer Castor. We are now directly above Orion. Keep circling, now down and to the right, until you run into Capella in Auriga the charioteer. Keep circling down and somewhat left (through Venus) and to Aldebaran, the red eye of Taurus the bull. Then keep circling back to your starting point, the Belt Stars.

Orion's most famous object shows on this picture as a faint fuzzy patch below the belt stars. This is the Orion Nebula, a stellar nursery filled with young bright stars that light up the surrounding interstellar gas. In long exposure photographs, the nebula will be mostly red (emission), with some blue (reflection) around the brightest stars. However when using binoculars or a small telescope, the nebula will appear greenish grey. That's because it takes very bright objects to active the cones that provide our colour vision - the rods that provide our night vision are colour blind.

The Orion Nebula is merely the tip of the iceberg. Orion marks the (relatively) nearby outer arm of the Milky Way galaxy, so is rich in interstellar gas energized by young stars. Don't expect to see most of the objects revealed by professional photos though, not unless you have a large telescope, perfect seeing conditions and a lot of patience.

* southern for people in the northern hemisphere. For people in the southern hemisphere, Orion is standing on his head so you need to flip the "up-down" references.


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October 2012

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