Download February 2012

The Night Sky
February's Procession of the Planets
Readers may have noticed from their calendars that February has an extra day this year. 2012 marks a
"leap year". With some special exceptions, February contains a leap day for years that are evenly
divisible by four. This is because the Earth does not take 365 days to orbit around the Sun; instead, it
takes closer to 365 and a quarter days. Leap days keep our calendars on track so that in the long term,
January does not slide into summer months and June into winter ones.
February turns out to be an excellent month for viewing the planets. Mercury, Venus, Mars, Jupiter, and
Saturn all make appearances in the night sky this month. Mercury, being the closest planet to the Sun, is
difficult to see in the sky as planet hunters must look for it low toward the horizon just after sunset or
just before sunrise. The end of February will offer sky viewers one of the best opportunities of the year:
Mercury will be a bright "star" located about 10 degrees above the western horizon shortly after sunset.
Venus and Jupiter are both in the west in the evening, with Jupiter appearing lower toward the horizon
as March approaches. Notably, a waxing crescent Moon will be near Venus on the 25th, and then it will
be near Jupiter on the 26th. Seeing a bright planet adjacent to a waxing Moon is always an impressive
sight! In addition, Saturn presents a good view of its rings this month. Early in February Saturn will rise
fairly late. However, by end of the month, a good view of Saturn will be achievable well before
midnight.
Mars offers especially curious behavior for the next couple months as the planet will execute a
"retrograde loop" in the constellation of Leo the Lion. The word "planets" literally means "wanderers".
In our view of the sky, planets appear to move or "wander" smoothly from one constellation to the next
along the sequence of the Zodiac. However, as the Earth moves around the Sun, our view of planets
occasionally makes them appear to reverse their motion. Mars will have appeared to stop moving on
January 24th, and a backing up motion will proceed until mid-April. Careful observers can use Regulus,
the brightest star in Leo, as an ideal fixed marker for noting Mars' retrograde motion during this period.
In closing, it is worth noting that the constellation of Orion remains prominent in the sky for February.
The Hunter will be most nearly overhead in the sky between about 7 and 8 at night. For those craving
more of a deep sky view, the Orion nebula (or M42 in the Messier designation) is an excellent target.
The nebula is the middle "star" of the three stars that make up Orion's sword. But it is not a star at all,
rather it is a stellar nursery, a place where new stars are forming out of a large gaseous cloud in space.
Even binoculars will be sufficient to see the nebula as a fuzzy patch of cloud suspended in space.
The next free public astronomy open house at the ETSU Powell Observatory will occur on Saturday,
February 25th from 8:00 to 10:00 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.
This month’s Night Sky was written by Dr. Richard Ignace, Department of Physics and Astronomy. He
can be reached at [email protected]. Astronomy-related information for the public, including a link to
the ETSU astronomy open houses, can be found at http://www.etsu.edu/physics/astronomy.htm.