The moon is on its last quarter, not even rising until long after midnight, waning towards new, so the evening skies are dark.  All you need is clear weather to familiarize yourself with the constellations of the winter southern sky.  Using each constellation as a handhold to the next, you can learn to identify several prominent ones.  The night sky used to be an essential part of human culture – nightly entertainment, the stuff of legend, oral tradition, spiritual heritage, and the cornerstone of navigation that helped sailors explore our globe.  Knowing a little bit about what’s where can help you fix your own position in time and space.

Orion, the hunter, is the brightest constellation in the sky (in terms of average luminosity of all its stars), as well as one of the most easily recognizable.  Laying in the south just after dark, the three stars of Orion’s belt are almost vertical, and his sword hangs from his belt, to the right.


The majestic Orion Nebula imaged with the 2.2m ESO/MPG telescope.

You may not have realized it, but the center star in his sword is not a star at all – this is the Orion Nebula (NGC 1976, M42), a breeding ground for new stars that is easily visible with the naked eye, and one of the easiest nebulae to find and observe with a small telescope.  It’s so bright, your eyes register it as another star, but look away from it slightly on a clear night and you’ll notice it’s actually a fuzzy cloud, one that is estimated to be 24 light-years across.  With a telescope, you can see all sorts of features embedded in this nebula, illuminated by the young stars within it.

Orion has some other interesting features.  The reddish star in the upper left shoulder (your left, not his – at least not if you picture Orion facing you), is Betelgeuse (pronounced “beetle juice”), a massive red giant that astronomers believe will one day explode as a dramatic supernova.  If Betelgeuse were in the center of our solar system, its surface would extend beyond the asteroid belt, completely engulfing the orbits of Mercury, Venus, Earth, and Mars.

stars-orionOn the opposite corner, in the right knee (your right), is Rigel (“Rye-gel”) a hot, blue-white supergiant.  Rigel is actually a quadruple star system – a much dimmer companion, Rigel B, is itself a binary, where two stars are tightly orbiting each other with a period of just under 10 days.  Rigel C orbits this pair every 63 years or so, and together this cluster of 3 dimmer stars orbits the main supergiant at an estimated period of 18,000 years.

Orion’s dimmer stars, off to his right, are depicted as either a shield, a bow, or the skin of an animal he’s already caught, being held out in front of him.  I prefer the former interpretations, with his other arm raised high with a sword or arrow, because that gives the impression he’s actively fighting Taurus, the bull.

stars-orion-taurusIn Taurus, the bright red star Aldebaran (“Awl-DEB-er-ron”) sits at the point of a prominent “V” formation called the Hyades (“HIGH-a-dees”) – the face of the bull.  This cluster is the closest open star cluster to us, at about 153 light-years distant, and is actually a large spherical cluster where the brightest stars form the “V”.  Aldebaran, Taurus’s red eye, is not actually part of the cluster, but lies much closer to us (~65 light-years) along the same line of sight.

In Taurus’s shoulder is one of the more
beautiful open clusters in the sky, the Pleiades (“Plee-a-dees”), or the Seven Sisters.  Another test of eyesight, keen observers can resolve seven primary stars here with the naked eye, but even a pair of binoculars reveals many, many more in a cluster that is about 444 light-years from Earth.  Several legends from different cultures refer to this cluster as seven maidens that for various reasons were placed in the heavens – one Greek version of the myth tells that they were young girls who fled to the heavens to eNASA - Hubble Libraryscape the persistent advances of Orion, who, ironically, still chases them across the sky every night.

Below (to the south) of Orion, and rising above treeline a bit later, is one of the hunter’s faithful dogs, Canis Major.  Sirius, the “Dog Star”, is the brightest star in our sky, and relatively close at only 8.2 light-years.  Sirius marks the shoulder of the stick-figure hound that forms below and behind Orion.


Betelgeuse, Sirius and Procyon form the equilateral “Winter Triangle”

Finally, Canis Minor is a little more ambiguous as a constellation, following behind Orion – but its brightest star, Procyon (“PRO-see-yon”) is a binary star system that forms one point of the “Winter Triangle”.  This large, almost-equilateral triangle is formed between Betelgeuse, Sirius, and Procyon.

If it’s REALLY dark, the ribbon of the Milky Way should be apparent, extending from Canis Major vertically upward past Orion, almost through the zenith, down through Cassiopeia and out to the northwest.

Linking constellations like this, using one prominent feature as a hand-hold to find the next, is a great way both to familiarize yourself with what’s there and to start to form the mental map of the “geography” of the night sky, as well as to appreciate the natural beauty and scale of the universe.  Give some time to learning the stars, and you’ll be amazed some night when a glimpse of a constellation through a break in the clouds is enough to give you time, direction, and a little more confidence.

Get Out There!


2 thoughts on “Astronomy: Week of 1/22/17 (Orion and his Dogs Confront Taurus)

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