Two Planets Dominate Evening Sky
As we enter the year 2012, the month of January unfolds with Jupiter and Venus glowing prominently in the darkening southern sky after sunset.
The brilliant white radiance (magnitude -4.0) of the planet Venus is easily recognized a half hour after sundown low above the southwestern horizon. As the weeks pass Venus will progress higher and higher into the night sky. In a telescope Venus presents a dazzling white but small gibbous disk. At this time the view is rather uninteresting. That will change in April when the planet expands in apparent diameter and the phase shrinks to a crescent as it approaches Earth. A good astrophotographic opportunity will occur after sundown on January 26 with the crescent moon a mere seven degrees (almost a fist width at arm length in the sky) above and to the right of Venus above the southwestern horizon. Trees or buildings in the foreground will add depth to the picture.
Jupiter’s bright yellow glow at magnitude -2.5 is easy to identify high up in the southern nighttime sky amongst the faint stars of the constellations Pisces and Aries. Jupiter is well placed for observing with a telescope. Its four satellites (Io, Europa, Ganymede and Callisto) and two dark atmospheric bands are easily seen with small telescopes. The most alluring events with the satellites are the shadow transits where the satellite casts its black shadow onto the cloud tops of Jupiter. Most of the shadow transits are produced by Jupiter’s fastest orbiting moon Io. This satellite revolves around the Giant Planet in just 1.8 days therefore the transits last just over two hours in duration.
Just before midnight at the beginning of January the Red Planet makes its appearance above the eastern horizon. By month end Mars will rise about two hours earlier. As the Earth approaches Mars in its orbit observers will notice a marked change in the planet’s brightness. Its orange-red colour will nearly double in brightness from magnitude 0.2 to -0.5 throughout January. Mars is still too small to resolve any surface features in all but larger telescopes throughout January. Observers watching Mars will note its eastward (direct) motion, then halt (stationary) January 24 and commences a westward (retrograde) trek amongst the stars of the constellation Leo. Mars comes to opposition March 3 and closest to Earth on March 5.
Saturn rises around 2:00 a.m. EST in the east in mid-January. Residing in the constellation of Virgo its yellowish glow is easily seen at magnitude 0.7 amongst the fainter background stars. The brightest star of Virgo, which is near the brightness of Saturn, is Spica. This star is a blue-white giant about 250 light years distant and is 1,900 times brighter than our sun. Spica shines at magnitude 1.0 and is slightly fainter than Saturn. Saturn is located about seven degrees to the left the star Spica.
The waxing gibbous moon can be seen about four degrees above the planet Jupiter on January 2 after sunset. Looking south before sunrise on January 14 the waning gibbous moon will be found below Mars. The last quarter moon will be seen forming a tight triangle with the star Spica and Saturn on January 16 before the sun rises.
The Earth revolves around the sun in an elliptical orbit so we are farthest from the sun at one point and closest six months later at the opposite point. On January 4, 2012 the Earth is at its closest to the sun (perihelion) at a distance of 147,097,334 km (91,406,283 miles). Since the northern hemisphere is tilted away from the sun this time of year we receive fewer hours of sunlight each day (winter season). The southern hemisphere is tilted toward the sun giving them the summer season now. It is the Earth’s tilt towards and away from the sun that affects our seasons rather than the relatively small variation (3.4 percent) in earth to sun distances over the year. The Earth will be at its farthest point from the sun (aphelion) on July 4, 2012 six months from now.
Have a Happy New Year and look forward to those clear and dark nights in 2012…