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The brighter stars

January 22, 2013
By MICHAEL?RECTOR - www.adirondackastro.com , Adirondack Daily Enterprise

You may have already noticed that the sun is setting later and later as the days go on. As the sun sets and the skies have that ruddy color to the west, the higher in the sky you look the darker it is and even darker so to the east.

One of my favorite things to do as the sky is still bright and the sun is setting is that I like to look for the first few stars that begin showing up before it gets dark enough for all of the start to begin to show.

One of the very first objects to appear in the sky as the sun starts to set isn't a star at all, but a planet: Jupiter. The gas giant is one of the brightest objects in our sky this time of year - at a magnitude of minus 2 - and at the moment it is around 50 degrees above the ESE horizon as the skies start getting dark enough for it to start to show.

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With your unaided eye, Jupiter may look like a very large star in the sky with a slight yellow or orange color to it. If you hold a pair of binoculars to your eyes and look towards Jupiter will see that it is definitely not a star, and that there are bands of clouds covering this giant planet. Also, you will notice four bright objects close by, which are four of Jupiter's brightest moons (in order of distance from the planet) Io, Europa, Ganymede and Callisto. These are also known as the Galilean moons since they were first discovered by Galileo Galilei at the end of 1609.

The next bright star you notice after finding Jupiter is close by in the constellation Taurus, and known as Aldebaran. This bright star is around a 1 magnitude, and is known as the eye of the bull. Sixty five lightyears away from Earth this red giant star shines brightest in the constellation and is also one of the brightest stars in our night sky.

The name Aldebaran is an Arabic name, which translates to "the follower," due to it appearing to follow the star cluster M45, also known as the Pleiades, or Seven Sisters.

Near Aldebaran is another bright star in the constellation Auriga, which is commonly called,

Capella. This yellowish star is around a 0 magnitude, making it a little brighter than Aldebaran in

our sky, and third brightest star in the northern celestial hemisphere.

To our eyes, when looking up at Capella, it appears to be one single bright star, but it is actually four stars in two binary pairs. The two brightest stars are about 10 times our sun's radius, and the other two stars are faint, small and relatively cool in comparison, but believed to be expanding on their way to becoming red giants.

Next we move down lower in the sky before the sun sets. In the constellation Orion you may first spot the red supergiant Betelgeuse and the blue-white supergiant star Rigel at magnitudes 0.5 and 0.1 respectively. Rigel, the brightest star in Orion, comes in as the sixth brightest star in our skies, with Betelgeuse coming in at number eight. These two stars are easily distinguished by their colors; Betelgeuse is a distinctly red color, and Rigel is a blue/white color and seems to be a bit more intense in brightness even though the two are close in brightness.

Now that it's dark you may have noticed that another very bright star has started to appear just above the southeastern horizon, and below the constellation Orion. This bright star is known as Sirius and is the brightest star in our sky. It is in the constellation Canis Major at a magnitude of minus 1.5. Sirius is a white main-sequence star (in stellar "middle age"), and is bright due to its natural luminosity and the fact that it is quite close to Earth at a distance of 8.5 light years. This is the closest star to our sun that can be seen with the unaided eye, and is slowly moving closer to the Solar System. Don't worry though, it will get only slightly closer over the next 60,000 years before it starts to recede. Sirius isn't just one star either, it's actually two stars, but the one you see is the brightest of the two with the other star being a faint white dwarf.

Once the sky is dark and the sun is gone for the night you have a whole sky full of stars to look at in a wide range of magnitudes. Now is a great time to dust off that old pair of binoculars you have laying around, and begin scanning the sky to notice more stars.

You may even come across some nebulae (fuzzy clouds of gas and dust) as you move around. Also at this time you may have noticed how much the stars you were looking at have moved a significant distance in the sky. Over the course of an hour the stars have moved 15 degrees to the west.

To get an idea of how much 15 degrees is hold your arm out fully extended and from the tip of your index finger and the tip of your pinky finger stretched out is roughly 15 degrees. The best part about measuring distance this way is that it's proportional to your age and size, so whether you're an adult or a child this is a good way to quickly take the measurement. Some more measurement tips using your hand fully extended; Width of your pinky is 1 degree; Width of your ring, middle and index fingers together equals 5 degrees; width of your fist equals 10 degrees; width from tip of your thumb and pinky finger stretched out equals 25 degrees.

I hope you get the opportunity to catch some of these bright objects as they begin to appear in your sky, and if you're anything like me you will find yourself out there well past the

setting sun and you'll be enjoying the night sky and all the wonders it holds. Enjoy one of the greatest shows on Earth by stepping out and looking up. Also, be sure to dress warm this time of year especially since some of the coldest nights are also some of the clearest nights.

Beyond this column, local astronomers are anxious to share our love of the sky with you. Check out my website at adirondackastro.com for descriptions and explanations of celestial objects. Also, visit the Adirondack Public Observatory website at apobservatory.org for

information about local and celestial events. Listen for Aileen O'Donoghue on North Country Public Radio about once a month during "The Eight O'clock Hour" or email her with any questions at aodonoghue@stlawu.edu.

 
 

 

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