If you’ve been watching Orion in the evening sky, you may have noticed that Orion is appearing lower and lower in the west each night as he prepares to leave us for the summer.
I like Orion, so this is a somewhat sad time for me. If you have kids who can find Orion, this might be a sad fact of spring for them too. Here’s what you can tell them about where Orion is going and what is taking his place:
Orion is a winter constellation, meaning he is easily found in the winter night sky. Over the course of each night he shifts westward across the sky because the Earth turns, giving us our night and day and making the Sun and stars appear to move across the sky. Also, each evening when the stars come out he appears a little further west than he was the night before, because the Earth revolves around the Sun, giving us our year, and shifting our point of view in space. This revolution around the Sun makes the constellations we can see shift westward in the sky over the course of the year. We will no longer see Orion after the spring because the Sun will be between us and him, and we will have to wait until our travels around the Sun bring him into view again.
When does Orion disappear? It depends on your location, but the further north you are on Earth, the sooner he disappears. According to an EarthSky post about “The Westward Shift of Orion and All the Stars:”
The farther south you are, the longer you can see Orion. But for the central U.S., Orion is lost in the sun’s glare by early to mid-May (depending on how carefully you look for it). And for all of us in the U.S., Orion is gone by the time of the summer solstice in June.
He starts reappearing in the eastern sky before dawn in July, each night rising a little earlier, so in September he is above the horizon in the east around 3-ish a.m., around 1-ish a.m. in October, and around 10-ish p.m. in November, and so on.
So what is taking Orion’s place in the southern part of our sky?
Spring constellations are relatively tame. By this I mean there are fewer strikingly bright stars and constellations, especially when compared to the bright stars of winter (Betelgeuse and Rigel in Orion, Procyon in Canis Minor, Sirius in Canis Major, Aldebaran in Taurus, Capella in Auriga). The bright stars of the spring sky are Arcturus in Bootes, Spica in Virgo, and Regulus in Leo. The constellations in the south-facing sky in late-April evenings are Virgo, Leo, Corvus, Crater, and Hydra. (In this post I will show you how you can point out Leo and Virgo to kids. I will cover Corvus, Crater, and Hydra in another post, which I hope to publish soon.)
In an earlier post about Mid-April Stargazing 2012 I showed you a trick for finding Leo: look for the Big Dipper high overhead; imagine it filled with water; poke a bunch of holes in the bottom of the bowl, and you’ll rain water down on Leo. (See the Mid-April post for an illustration of this trick.) There are a couple of tricks for finding Virgo.
First, find the bright star in Virgo named Spica (SPIKE-uh). You can do this by finding the Big Dipper, which in springtime evenings is high overhead. The handle of the Big Dipper is curved, like an arch. If you follow the curve, you can “Arc to Arcturus,” which is a bright, ginger-colored star in Bootes the Herdsman (BOH-oh-teez), who looks like a kite when you just connect the dots of Bootes. (A note about seeing Bootes: in following the arc to Arcturus, you end up tracing out one side of the kite-shape.) From Arcturus, you continue the arc and “Speed on to Spica.” From there, good luck, because the rest of her is pretty dim! No, seriously, look for stars that make a Y-shape to the right, and there are some leg-like connect-the-dots stars off to the left of Spica.
Virgo can be a difficult constellation to visualize. If you see drawings of her, she is usually depicted as standing with arms down, holding a wheat stem (Spica); the right side of the Y-shape points to her head; the left side crosses her body.
I prefer to imagine her slightly differently. To me, the Y-shaped part looks like outstretched arms; the closed polygon a body; the leftward pointing lines legs. And she’s just to the left of Leo, stretching those arms up to him. I like to think of her as saying, “Oh! What a beautiful lion. I want to give him a big hug!” (And, yes, I like to point her out this way in the planetarium.)
The EarthSky post about Orion suggests an astronomy activity to do with your kids:
If you want to notice the westward shift of the constellations due to the passage of the seasons, be sure to watch at the same time every night. If you want to watch their westward shift throughout the night, just pull up a lawn chair and watch.
While you watch Orion, point out the Big Dipper, Arcturus and Bootes, Spica and Virgo, and Leo. As an added bonus in 2012, the “red star” in Leo is Mars, and the “other bright star” by Spica is Saturn. I’ll get a post up about Corvus, Crater, and Hydra for your other viewing night for when you go out to note how much Orion has shifted due to the seasons.
Also, while Orion is still here, take a look at what he has to offer stargazers. I mention his differences in star color in my Mid-April post, and this one from Universe Today gives a good guide to doing a binocular tour of Orion. Enjoy him while he lasts! For all too soon the Earth will wrench us apart and the Sun will come between us. <tears>