Winter’s Glittering Sky Gems

By Irwin Horowitz, 1-01-08

Winter skies are dominated by a number of bright stars located in well recognized constellations.  The most prominent of these stellar groupings is Orion, the Hunter.  This constellation has a multitude of bright, easily discernible stars which present a figure that unlike many other groupings actually looks like its namesake!  It is dominated by a ruddy star in its right shoulder, Betelgeuse (pronounced Beetle-juice) and a brilliant sapphire blue star in its left knee, Rigel.  Through Orion’s midsection a line of three bright stars form his belt (from left to right: Alnitak; Alnilam; and Mintaka). 

Beneath the belt lies his sword.  The middle “star” in the sword is actually one of the most well known nebulae in the night sky, called appropriately enough, the Orion Nebula.  This nebula is actually a hotbed of stellar birth and infancy.  This entire region of space represents one of the most active stellar nurseries found in our galaxy, with many fascinating features associated with this activity such as the Horsehead Nebula. 

Above Betelgeuse, a grouping of fainter stars form a club shape that Orion is holding over his head, while further west a string of stars form a shield to protect the hunter from Taurus, the Bull.

Taurus is dominated by two features, the orange star Aldebaran and the Pleiades star cluster.  Aldebaran represents the “eye” of the bull, with his head formed by the “V” shaped series of stars in this region known as the Hyades cluster.  Even though Aldebaran appears near the Hyades, it is actually much closer to our solar system and is not actually a member of the cluster. 

The Pleiades is located further west and consists of many bright stars which appear to glitter like diamonds on black velvet when viewed through binoculars or a small telescope.  This cluster formed fairly recently in astronomical terms, about 100 million years ago.  Its members were often associated with a group of sisters in many ancient myths (“the seven sisters”). 

If one follows the pair of horns above the bull’s head to their tips, you can find the location of one of the youngest supernova remnants in our sky, the Crab Nebula.  It can be found just to the west of the star zeta Tauri (the horn tip closest to Orion’s club).  The expanding cloud of gas was material that was expelled in a massive explosion that was observed by many cultures back in 1054 A.D.  The explosion left behind a superdense sphere of neutrons spinning around at 30x each second.  This object is known as a pulsar.

This month we find the planet Mars hovering in this region between the tips of the bull’s horn.  Last month, the planet was in opposition a few days after its closest approach to Earth.  It will continue to be a bright object easily visible in our night sky into this summer.

From Taurus’ horns, we travel northward to Auriga, the Charioteer.  Its bright yellow sun is called Capella, and it forms a rough hexagonal shape with half a dozen other stars in its vicinity.  The most interesting features found here are a series of open star clusters, M36, M37 and M38.  Each makes a fine object in a pair of binoculars or a small telescope.

To the east of Auriga lies Gemini, the Twins.  Its two brightest stars are Pollux and Castor.  The Castor system actually consists of six individual stars, found in three separate pairs in mutual orbits around each other.  The open cluster M35 can be found in Gemini.  It is brighter than the three clusters found in Auriga, though not as prominent as the Pleiades cluster.

Below Gemini we find a pair of canines, Canis Minor and Canis Major.  Canis Minor, aka “hot dog” consists of only two visible stars.  Don’t try to convince yourself that it appears anything like a dog.  The brighter star is called Procyon (pro-cee-on).  It is one of the closest stars to our own solar system and is slighter bigger and brighter than our own Sun.

Canis Major, the great dog, does actually look like its namesake.  It appears to be standing on its back legs as it rises in the early evening hours in January.  Sirius, the “Dog Star” is the brightest star in our sky (save for our Sun) and is found in this constellation where it is often depicted as the diamond in the dog’s collar!

Together, these constellations and the bright stars that shine within dominate the skies during the frigid winter months.  I like to take note of the asterism known as the “Winter Hexagon.” It is made up of the six bright stars Rigel, Aldebaran, Capella, Pollux/Castor, Procyon and Sirius.  Near the center of this cosmic polygon lies Betelgeuse.

The Earth will pass by perihelion on 02 Jan around 5 p.m. MST.  At this time, we are at our closest point to the Sun.  Many people are surprised to learn that we are actually closest to the Sun in January and furthest in July.  The seasons are due not to our proximity to our parent star but rather to the inclination of our planet’s rotation axis relative to the plane of its orbit.

As for the other planets this month, Mercury makes a brief appearance in the evening sky in the latter half of January.  Venus continues to fade in the morning sky as it pulls further away from us in its orbital dance.  Jupiter returns to the pre-dawn sky by the end of the month.  Saturn rises in the early evening and is visible most of the night near Regulus in the constellation Leo the Lion.

Club activities in January include the monthly meeting of the Boise Astronomical Society on Friday, 11 January at 7 p.m. in the front section of the Discovery Center of Idaho.  After a brief business meeting we will assist new telescope owners in learning how to setup and use their instruments.