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The Night Sky
As promised in last month’s article, the world did not end on December 21, 2012. As the year 2013
begins, the earth passes through perihelion on January 2nd, its closest point to the sun in its elliptical
orbit. On this date, it is 3% closer to the sun as compared to its farthest point, or aphelion, in the
beginning of July. The sun is now starting to move northward on its yearly cycle around the sky. As a
result of this, sunsets start arriving later in the evening and sunrises start arriving earlier in the morning.
January’s full moon, known in folklore as the wolf moon, rises at sunset on January 26th.
In the evening sky, Jupiter continues to be the brightest star-like object. On January 21st, the moon
passes very close Jupiter in the constellation of Taurus, appearing no more than one degree below
Jupiter at 11 p.m. on this date. Some have speculated that such a close conjunction between the moon
and Jupiter in 4 BCE was the “star of Bethlehem” reported in the Bible.
Mars continues to lose “celestial ground” to the sun and will be very hard to spot in the southwestern
evening sky during twilight. Meanwhile, Saturn is in the constellation of Libra and rises around 2 a.m. on
New Years Day, however by months end, it rises around midnight.
Venus is racing towards the sun on the morning sky and now only rises one-half hour before the sun on
New Years Day. By the end of the month, Venus will be lost in the sun’s glare as it begins to pass behind
the sun in its orbit. Venus will be reappearing in the evening sky just after sunset later this winter.
Mercury will be lost in the solar glare all month but will be emerging from behind the sun in the evening
sky in February.
Assuming you can stand the cold evenings, the winter sky displays very prominent constellations,
especially the hourglass shaped constellation Orion which can be seen in the southeast around 10 p.m.
Orion can be used as a signpost to find other constellations and bright stars. Following Orion’s belt (3
relatively bright stars in a line) towards the southeast, one comes across the brightest star in the night
sky, Sirius, in Canis Major (the large hunting dog). Sirius is so bright due to its proximity to the solar
system being only 8.3 light years away. The bright star on the north side of Orion is the red supergiant
star Betelgeuse (pronounced beetle-juice), which means “armpit of the great one.” The bright star on
the south side of Orion is the blue supergiant star Rigel, which means “knee of the great one.” Following
the belt northward, one encounters the red giant star Aldebaran in Taurus and Jupiter.
Should the sky be clear the night of January 19th, there will be a free public astronomy open house at the
ETSU Powell Observatory from 8 to 10 p.m. At these open houses, the public can view objects in the sky
through telescopes and hear talks by faculty of the Physics and Astronomy Department. Note that the
open houses are cancelled if the sky is cloudy. Further information about these open houses and
directions to the observatory can be found on the web at
http://www.etsu.edu/cas/physics/observatory/starparty.aspx.
This month’s Night Sky was written by Dr. Donald G. Luttermoser, Chair of the Department of Physics
and Astronomy. He can be reached at [email protected]. Astronomy-related information for the
public, including a link to the ETSU Powell Observatory, can be found at
http://www.etsu.edu/cas/physics/outreach/astronomy.aspx.