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Starwatch: The tiny Christmas tree challenge

December 22, 2018

While there really aren’t any Christmas constellations this time of year, or any other time for that matter, there are two signs of the most wonderful time of the year among the stars. One is small and challenging to locate, and the other is large and very easy to spot.

First, the challenging one. Its nickname is the Christmas Tree cluster, but through a small telescope or even a decent pair of binoculars that’s actually what it resembles. It’s easier to see in the dark countryside, but even in light-polluted areas you should be able to spot it.

Formally in the astronomical books it’s known as New General Catalog Object 2264, or NGC 2264 for short. It’s also known as the Cone Nebula. You will have stay up a bit and do some digging to find the Tannenbaum among the stars, but once you find it, you’ll love it and want to share it with others. It’s so cute and hopefully it will still add to your holiday spirit.

After 8:30 p.m. or so, it will be high enough above the eastern horizon to start your search. The Christmas Tree Cluster resides in a very obscure constellation called Monoceros the Unicorn, that to me looks like a ham radio tower my Dad set up on top of the house I grew up in, much to my Mom’s objections.

Forget about trying to truly see Monoceros, it’s just so faint and ill-defined anyway. The best way to find it is to use the bright constellation Orion the Hunter, perched diagonally in the southeastern sky. I know you’ve seen it before. It’s the dominant constellation of winter, containing the three bright stars in a nearly perfect row that make up the belt of the mighty hunter.

On the upper left corner of Orion is a bright reddish tinged star called Betelgeuse that marks the armpit of the hunter. On the upper right corner of Orion is the star Bellatrix, not quite as bright as Betelgeuse. Draw a line from Bellatrix to Betelgeuse and continue that line to the lower left about 10 degrees from Betelgeuse. Ten degrees is about the width of your fist at arm’s length. Scan that area with your binoculars or telescope and you should eventually find it.

Early this week it may be a little tough to find it because of the full moon in the same area of the sky, washing out your view of fainter stars. If you wait until Christmas night, Dec. 25 or the next weekend the full moon will be waning and not rising until late at night, leaving the sky a lot darker.

Once you find the cluster, you’ll see that the 20 or so stars are arranged in the shape of a Christmas tree. What’s odd though is that the brightest star is at the base of the tree, not at the top where you would expect it. The brightest star resides on the base of the trunk. The starry little tree will appear to point to the lower right in binoculars and some telescopes However, most telescopes will give you an inverted view, so the miniature tree will point to the upper left.

The Christmas tree shape of the cluster is arguably a pleasant coincidence. The stars just happen to be arranged that way from our view of them on Earth. Like most open clusters, this is a group of young stars that formed out of a large nebula of hydrogen gas, much like our sun did more than 5 billion years ago. These clusters of young stars hang out together for several hundred million years until gravity from other surrounding stars break the clusters up.

The stars that light up the Christmas Tree Cluster send their tidings of great joy from a long, long ways away! They’re about 2,600 light-years distant.

For the Christian world, there’s also a really easy sign of Christmas that shines brightly in the early evening western sky and is easily visible to the naked eye. It’s the Northern Cross, and even in areas of moderately bright city lights you should have no trouble finding it.

The Northern Cross is actually part of a larger constellation called Cygnus the Swan, but it’s the brightest part of the constellation. Around 7 p.m. to 8 p.m., look about halfway up in the western sky for Deneb, the second brightest star you can see in that area of the sky. Just below Deneb, look for three fairly bright stars in a horizontal row that make up the arms of the cross. Below those three stars and closer to the horizon is a slightly fainter star, Albireo, that marks the base of the Northern Cross.

This is the only time of year that we see the Northern Cross standing nearly upright in the early evening.

Merry Christmas!

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