SKY HAPPENINGS

The Sky for January 2011
By Faylene Roth

DAYLIGHT
The January sun demonstrates little acceptance of the Winter Solstice’s passing. Sunrise occurs no earlier on January 11 than it did on December 30. The gain achieved from the sun’s northward movement is negated by an increase in the earth’s orbital speed. It affects the position of the earth relative to the sun after a 360 degree rotation. The earth must rotate a little farther to achieve sunrise, a little later. As the sun’s declination in the morning sky rises, it overcomes the effect of delayed sunrises. Daylength does increase during January by 42 minutes, due primarily to later sunsets. The delay in the time of sunset by a minute each day results from both the increase in the earth’s speed and the rising declination of the sun in the sky. Twilight also contributes to the appearance of longer days. Astronomical twilight brightens the horizon one and one-half hours before sunrise when the sun is still 18 degrees below the horizon. Nautical twilight begins one hour before sunrise when the sun is 12 degrees below the horizon. Civil twilight begins one-half hour before sunrise when the sun is six degrees below the horizon. The reverse progression occurs with sunset. Actual time of sunrise and sunset for a specific location depends upon the landscape.

MOON HAPPENINGS
January 4 – New Moon occurs at 2:03am
January 12 – First Quarter Moon sets after midnight
January 19 – Full Moon rises at 5:37pm
January 26 – Last Quarter Moon rises after midnight
(The time of moonrise and moonset assumes a flat horizon. Actual time may vary.)

METEOR ACTIVITY
A new moon on January 4 provides prime viewing conditions for the Quadrantid Meteor Showers, which are visible January 1-5. Its radiant is the constellation Bootes, which rises over the La Sal Mountains around 1:00am. Locate Bootes by extending the arc of the Big Dipper’s handle about 25 degrees to Arcturus, which is the brightest star in Bootes. At its peak, this meteor shower can produce 40+ faint, blue meteors per hour. Best viewing is during the morning of January 3/4 as Arcturus approaches its zenith. Several other radiants along the ecliptic provide good meteor viewing throughout January, up to 20 per hour. Best viewing for these meteors are the dark morning skies that precede astronomical twilight.

PERIHELION
Earth reaches its closest point to the sun on January 3 at 12 noon. Since the northern hemisphere experiences winter while the southern hemisphere experiences summer, it is obvious that the distance between earth and sun is not the cause of our seasons. The tilt of the earth’s axis claims that credit. Over a 21,000 year cycle, the time of perihelion will pass through every season. Perihelion and aphelion (farthest point from sun) can affect the intensity of the season in which it occurs, but it is just one of many factors that affect climate. (The difference in perihelion and aphelion is about 3,000,000 miles or 5 million kilometers.)

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.

VISIBLE PLANETS
Jupiter -The first light in the evening twilight this month is Jupiter. Look for it high in the southwestern sky at dusk. It sets before midnight with the constellation Pisces. During the first week of January use binoculars to find Uranus, the green planet, above and to the right of Jupiter. On January 5, it is one-half degree from Jupiter directly to its right. A waxing crescent moon hangs above the steady yellow light of Jupiter on January 10. (Magnitude -2.1)

Saturn - Watch Saturn rise in the southeastern sky around midnight--about one to two hours after Jupiter sets. It remains in Virgo throughout the year. Look for its steady yellow light above and to the right of the bright blue twinkle of Virgo’s bright star Spica. On January 25 Saturn hangs above a waning gibbous moon. (Magnitude +0.4)

Venus - Sometime between 4:00am and 5:00am each morning, Venus claims the morning sky. Its bright white light outshines every star and planet in the night sky. Venus begins the month in Libra. Each morning it rises a little later, which causes it to cross first Scorpius, then Ophiucus, and finally touch Sagittarius by the end of the month. A waning crescent moon hovers with Venus on the mornings of January 29 and 30. (Magnitude -4.4)

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.

Enjoy the holiday color of winter skies. Aldebaran (Taurus) and Betelgeuse (Orion) glow red, Pollux (Gemini) orange. Castor (Gemini), Capella (Auriga), and Procyon (Canis Minor), shine white. Rigel (Orion), Sirius (Canis Major), and the Pleiades twinkle in blue.

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.