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The Sky This Week, 2020 January 14 - 21

Now that winter's here is summer far behind?
The Great Winter Circle rising over the Northern Neck, 2019 December 30
The Great Winter Circle rising over the Northern Neck, 2019 December 31
Imaged with a Canon EOS Rebel SL2 DSLR and an Omegon mechanical star tracker
from Mollusk, Virginia, 2020 January 1.
Mosaic of five exposures, 1 to 2 minutes @ ISO 1600, EF-S24mm lens @ f/4.

The Moon glides through the morning sky this week, passing through the rising stars of spring.  By the week’s end you’ll find her joining the stars of Scorpius, the Scorpion, one of the signature star patterns of summer.  Last Quarter occurs on the 17thh at 7:58 am Eastern Standard Time.  Look for the Moon just east of ruddy Mars in the southeastern sky just before dawn on the morning of the 21st.

Before we start thinking about summer, though, we still have much of winter to get through.  Yes, the nights are now gradually getting shorter, but daylight still lasts less than 10 hours for much of the country.  The evening hours are dominated by the bright stars of the Great Winter Circle, the colorful arc of stars that are anchored by the distinctive constellation of Orion.  These stars cross the meridian between 9:00 pm and midnight local time, adding at least a bit of light to the season’s darkness.  

The westernmost star in the circle is Aldebaran, which casts a ruddy hue from its apparent position inside the V-shaped star cluster known as the Hyades.  Although it appears associated with the group, Aldebaran is only about half the distance to the Hyades’ stars, which lie about 120 light-years away.  Northwest of Aldebaran is another cluster, the famous Pleiades.  In mythology the Pleiades and Hyades were half-sisters and daughters of Atlas.  The Pleiades are located just under 450 light-years distant, and figure in the sky lore of almost every culture that has left us written records.  

From Aldebaran we move southeast to the star Rigel, the current brightest star in Orion.  Rigel’s stark blue tint contrasts with the distinct reddish hue of Betelgeuse, which marks one of Orion’s shoulders.  As mentioned last week Betelgeuse is undergoing a mysterious fading episode that has caused it to shine at about half of its normal brightness.  You can use Orion’s famous “belt” stars to point to the Circle’s next star, Sirius.  

Like Rigel, Sirius shines with a pleasing blue color, but physically the two stars are vastly different.  Sirius is the brightest star in the sky thanks to its relative proximity just over eight light-years away.  It is a “main sequence” star, somewhat hotter and more massive than our Sun, happily enjoying “middle age” in its evolution.  Rigel, on the other hand, is a “supergiant” star, over 20 times a massive as the Sun and some 100,000 times more luminous. Its distance is over 100 times that of Sirius.  Such a massive, luminous star won’t last long on the cosmic scale.  Rigel is thought to be less than 10 million years old, and it will probably explode in a massive supernova explosion time sometime in the next 200,000 years.

North of Sirius is another nearby star, Procyon, lead star in Canis Minor, the Little Dog.  It is similar to Sirius, but slightly cooler and a bit further away at 11.5 light-years.  

North of Procyon we find the Twin Stars of Gemini, Castor and Pollux.  Pollux is the brighter of the pair, located about 33 light-years from the solar system.  It is a Sun-like star that has evolved to its “giant” stage, beginning its slow journey to a white dwarf billions of years from now.  Castor is a pleasing double star in the small telescope, but in actuality it is a complex system of at least six components.  It is 51 light-years away.

The circle’s northernmost star is yellow-hued Capella, the third-brightest star in the northern sky.  Like Castor, it is actually a system of multiple stars consisting of four components, located 43 light-years from us.  

Together the stars of the Great Winter Circle show us a nice “cross section” of the variety of stars that travel with us in the Milky Way.  Within its confines we find nine of the sky’s 25 brightest stars, perfect companions to get us through winter’s long nights.

Within our solar system, Venus continues to vault into the evening sky.  She is almost impossible to miss in the southwest after sunset, and she lingers for an hour and a half after the end of evening twilight before setting.

The only other bright planet we can see in the current sky is Mars, which may be spotted in the southeast in the pre-dawn hours.  Mars is easily identified by his reddish tint and his rapid motion past the star Antares.  He will pass five degrees north of the star on the morning of the 16th.  He will entertain the waning crescent Moon by the end of the week.

 
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