Surely the clouds will part and allow a little starlight in. That other variety of stars, the cold, crystalline type, has been falling every day and night the past week. I love snow, but I’m ready for night’s twinkly points of light, even it means suffering the colder weather that often accompanies clear skies in winter.
Just the same, and with optimism ever in my heart, we’ll visit another constellation cluster today. This one centers on Orion the Hunter and includes Lepus the Hare and Eridanus the River. And don’t worry about clouds. These guys will be out from now until the end of February. It’s gotta clear out sometime.
Orion’s easy to find. Look southeast around 7-7:30 p.m. and midway up in the sky you’ll see the “three stars in a row”. They represent the hunter’s Belt. Below the Belt is a small group of fainter stars called the Sword. The middle one looks mistier than the others – that’s the Orion Nebula, one of the sky’s brightest clouds of dust-ridden gas set aglow by newborn stars within. Binoculars will show a couple bright stars swaddled in a pale white cloud. Telescopes and time-exposure photos reveal just how beautiful and complex this nebula is. Even a small scope shows its pale neon-green color caused by excited oxygen atoms.
If your sky is reasonably dark, try expanding your concept of the Hunter to include his club – a trail of dim stars north of Betelgeuse – and his shield, a wriggly line of suns about one fist held at arm’s length to the right of Betelgeuse.
Attempting to hide out below Orion but in plain site nonetheless is a rabbit, better known as Lepus (LEE-pus) the Hare. The pattern of the brightest stars reminds me more of a dragonfly, but if you include the fainter ones that represent his ears, the form suddenly looks a lot more rabbit-like.
The name Eridanus (eh-RID-uh-nuss) comes to us from the ancient Greek word for the Po River in northern Italy. The long, sinuous constellation begins above the bright star Rigel in Orion and winds its way just like a real river across a vast wilderness of celestial real estate marked by few bright stars. From mid-northern latitudes, the river appears to end at the horizon.
Ah, but it doesn’t, and another clue tells us that there’s more to this constellation than most northerners ever see. You may have noticed in the map above that the river’s Alpha or brightest star is missing. Beta and Gamma Eridani, the second and third brightest stars, are represented, but not the constellation’s crowning glory. To see Eridanus’ brightest star, Achernar (AK-er-nar), you’ll need to fly down to Key West, Florida or points further south. This sounds like a particularly good idea right now.
Achernar is the ninth brightest star in the sky and a fitting end to our long river journey. Its name derives from the Arabic Al Ahir al Nahr and means “end of the river”. This star is special in another way – it spins at the incredible rate of 155 miles per second. Compare this to our sun’s rotation rate of about once every 27 days! Because stars are not solid balls of matter like planets but composed of pliable gas, when you spin a sun up to Achernar’s demon speed, it flattens out. The river’s Alpha star is one of the flatter ones known with a radius (distance from its center to edge) 50 percent larger at its equator compared to its poles.
I saw Achernar years ago in Aruba, an island off the coast of South America. After weeks of preparation in advance of a total solar eclipse, I finally reached the end of Eridanus while standing on the beach my first night there. It hit me like a surprise ending to a long, twisty tale.