UT (at City Hall)
38O34’ N Latitude 109O33’ W Longitude
4048 ft - 1234 m
The Sky for February 2012
Enjoy an additional 64 minutes of sunlight this month as the sun’s position on the ecliptic rises higher each day. Usable light is extended by about 30 minutes at each end of the day when the sun is no more than six degrees below the horizon. At dusk, this period—known as civil twilight—fades into nautical twilight over the next half hour. During nautical twilight the sun is between six and 12 degrees below the horizon. Color is less visible in the landscape when the sun drops this low. The last half hour of twilight—astronomical twilight—is marked by dark skies overhead and minimal light around the horizon. The reverse progression occurs at dawn.
RED GIANT STARS
Pollux (lower twin of Gemini) measures 34 light years from Earth, is nearly nine times the diameter of the Sun and 32 times more luminous. Aldebaran (lower horn of Taurus) lies 65 light years from Earth, spans 40-50 times the diameter of the Sun and is more than 150 times more luminous. Betelgeuse (bright shoulder of Orion) is 500 light years distant, 650 times the Sun’s diameter, and 9400 times more luminous. These stars are red giants, swollen stars that have exhausted their primary fuel sources and are in the final stages of their life spans. Having exhausted their primary hydrogen fuel, they are fusing helium into carbon and oxygen. Once helium is exhausted, carbon and oxygen become the fuel source for nuclear fusion and produce nitrogen, magnesium, and heavier elements. More massive stars have shorter life spans than the Sun, so astronomers calculate that these stars are much younger than the Sun even though they have progressed farther in their life cycles. Pollux is rich in carbon and oxygen, Aldebaran rich in magnesium, and Betelgeuse is rich in nitrogen. Only Betelgeuse has sufficient mass to continue fusing heavier elements until it becomes an iron-rich star that inevitably collapses on itself to produce a supernova, but, even it, may not be massive enough to form a black hole at its core.
February begins with a waxing gibbous moon overhead each evening. After the full moon, moonrise is delayed by more than one hour each night. By the time of the last quarter moon, the evening skies are dark until after midnight and will remain dark until a few days after the new moon when a thin crescent reappears above the western horizon.
Feb. 7 – Full Moon occurs at 2:54am and rises at 6:00pm
Feb. 14 – Last Quarter Moon rises shortly after midnight.
Feb. 21 – New Moon occurs at 3:35pm.
(The time of moonrise and moonset assumes a flat horizon. Actual time may vary.)
No major meteor showers occur during February but watch for fireballs along the ecliptic that can be as bright as Jupiter or Venus. These large meteors often blaze across the sky without the signature tail of light that accompanies most meteors.
Note: Hold your hand at arm’s length to measure apparent distances in the sky. The width of the little finger approximates 1.5 degrees. Middle, ring, and little finger touching represent about 5 degrees. The width of a fist is about 10 degrees. The fist with the thumb extended at a right angle equals 15 degrees. The hand stretched from thumb to little finger approximates 20-25 degrees. The diameter of both the full moon and the sun spans only 0.5 degree. Adjust for the size of your hand.
Primary Sources: USGS; U.S. Naval Observatory;
Your Sky at http://www.fourmilab.ch/yoursky/
To find out when the space shuttle and International Space Station are visible
from your location, go to:
http://spaceflight.nasa.gov/realdata/sightings/index.html and click on Sighting Opportunities.
Jupiter - The faint autumn constellations that linger overhead pale in the wash of Jupiter’s brightness. The brilliant gas planet rises earlier each day which puts it lower in the western sky each evening. By month’s end it sets well before midnight. Aries is above and to its left. (Magnitude -2.3)
Mars - Look for the flat red disk of Mars a few degrees below Leo’s triangular tail. Mars rises a few hours after sunset then remains in the sky throughout the night. It entered retrograde motion in late January which means its position relative to Leo retreats westward for the next several months. Retrograde motion occurs when Earth—on its inner orbit—speeds past Mars. It’s like passing a car on an oval track and watching it recede even though it’s still moving forward. As the Earth moves around the arc of its orbit, Mars real eastward movement will again be apparent. Mars brightens throughout the month as it approaches opposition (closest point to Earth) in early March. (Magnitude -0.9)
Saturn - Night owls and early risers can view the bright golden glow of Saturn. It rises almost due east with Virgo near midnight and has moved to the western sky by morning twilight. Saturn continues to brighten over the next few months as its orbit moves closer to Earth. (Magnitude +0.5)
Venus - The brightest of all planets viewed from Earth is losing face right now. From our perspective, Venus waxes and wanes just like the moon. Since it’s currently moving closer to Earth, the planet actually becomes brighter as its phase wanes from gibbous to crescent. As always, it outshines Jupiter which appears above it in the evening sky. On February 9 binoculars will reveal the green orb of Uranus less than one-half degree to the left of Venus. (Magnitude -4.1)
Note: Apparent magnitude values range from -4 to +6 for most planets and visible stars. The lower the value the brighter the object. A decrease of 1.0 magnitude is 2.5 times brighter.
CONSTELLATIONS this MONTH
Bright red Betelgeuse (Orion), sparkling blue Sirius (Canis Major), and bright white Procyon (Canis Minor) mark the points of the Winter Triangle. The Winter Hexagon surrounds Betelgeuse. Trace the hexagon from Sirius to Procyon to Pollux (Gemini) to Capella (Auriga) to Aldebaran (Taurus) to Rigel (blue star at foot of Orion).
Hold the star chart high above your head and match the compass directions to the direction you are facing. Adjust the star chart by orienting Ursa Major (Big Dipper) to match its position in the sky.
The star chart approximates the sky from astronomical twilight to midnight. As the night and month progresses, the constellations shift toward the northwest. The celestial equator is measured in hours (h).
The ecliptic is measured in degrees.