This month so far the sky has not been especially friendly for star-gazing. Besides lots of clouds, the big problem with observing in winter is a simple one: it’s cold! In the summer it’s easy to linger at the telescope, waiting for unexpected objects to pass into view or searching for new, hard-to-find targets. In the winter, targets that can be found quickly—before the fingers start to numb—and easily are better.
Fortunately, many of the celestial targets in the January sky are indeed bright and easy to spot quickly. Last month I started with an introduction to the constellation Orion. This month we’ll zoom into some of its telescopic wonders that can be caught on the frigid, (hopefully) clear nights of January.
As I’ve mentioned in this column in the past, I’m partial to observing double and multiple stars with my backyard telescope. These objects are bright enough to find in the light-polluted skies of town, and they’re endlessly varied. The most spectacular object to view in Orion is of course the Great Nebula (which we’ll examine in a moment), but Orion also hosts several lesser-known but lovely and easy multi-star targets.
We’ll start with the easiest target. Mintaka is the westernmost star in Orion’s belt. Through a modest telescope (I usually use a Dobsonian reflecting telescope with a 6-inch aperture) at low magnification (48x), it’s clearly revealed as a wide double star. It doesn’t have the impressive color contrast of a famous pair like Albireo, but with a separation of about 50 arcseconds, it’s easily revealed as a double even in a pair of binoculars.
Things get more impressive swinging the telescope just slightly eastward to the star sigma Orionis, the moderately-bright star visible just beneath Alnitak, the easternmost star in Orion’s Belt. Sigma is actually a triple-star system, with a few other surprises in the field of view. The components of the star are much tighter (closer together) than Mintaka, so I use a higher magnification (60x). The differing colors of this triple star are easily apparent and to my eyes seemed reddish, blueish, and whitish (though part of the fun of observing multiple-star systems is that each observer seems to note different tints). Even more impressive: in the same field of view, just to the west, is another, dimmer triple star system, Struve 761!
If your fingers are freezing, don’t despair: the next sights are well worth the chill. Move the telescope to the cluster of stars marking Orion’s sword. For now, pass up the Great Nebula (also known as M42) for the star at the southernmost tip of Orion’s sword. This is iota Orionis. Iota is a close pair (separation of 11”, I viewed it at 70x magnification): a bright star with a dim companion. In the same field of view though, is the wider, even pair of Struve 747. But that’s not all: a fainter third double star, Struve 745, can also be spotted in this view.
Finally, the most famous multiple-star system in Orion is buried at the heart of Orion’s most famous sight: the Great Nebula. Just north of iota, you can’t fail to spot it on clear nights. The four stars of the Trapezium are surrounded by the cloudy glow of the Nebula, which extends across the entire field of view in greenish, hazy ribbons. The larger your scope (and the darker your sky) the more detail you’ll see, but even with a 6-inch from my front yard in town, it’s a sight to brave the cold for.
We still have not exhausted Orion’s treasures though. Part of the appeal of searching after double stars is to tackle more challenging pairs: pairs that are either very close to each other or have a significant contrast in brightness. If you’re up for a challenge, try the star lambda Orionis, marking Orion’s head. This is an even double star with a separation of only 4 arcseconds (remember that Mintaka’s components were 50 arcseconds apart). With my 6-inch, I can easily split it on a clear night with a magnification of 70x. Compare this with Rigel, the brilliant star of Orion’s foot. Rigel has a dim companion at a distance of 10 arcseconds, but the brightness of Rigel makes it very hard to spot this pale blue companion star. On my most recent attempt, it took a magnification of 133x to spot it for sure.
I hope I’ve convinced you that Orion is a treasury of sights that make it worth braving the cold this month. Perhaps though you don’t have a telescope to take a look yourself and you’re wondering about the type of instrument to purchase to get started, or maybe you got a telescope this Christmas and you want to know more about how to put it to use. Next month I’ll spend some time going over telescope basics and providing my own thoughts on steps toward easy backyard observing.
This column first appeared in the Kankakee Daily Journal.