Jupiter and the Winter Hexagon

On January 1 at 9 p.m. PST the Earth passes closest to the sun in its yearly orbit, or perihelion. During perihelion, the Earth is 0.9833 AU from the sun, as compared with aphelion, when Earth is 1.0167 AU from the sun. The difference is about 5,000,000 kilometers between the two, out of a distance that averages around 150,000,000 kilometers. This small variation is not what causes the differences in our seasons, but the angle of the sun’s rays as they strike our tilted Earth. Because perihelion happens to coincide with the winter season in the north, it is possible for the coldest day of the year to be the day we are closest to the sun, and vice versa.

The year begins with Mars low in the southwest at sunset and Jupiter high in the southeastern sky in Taurus. Mars shines at magnitude 1.2 with an orange hue and Jupiter is an eye-catching point of light at magnitude -2.7.

Jupiter is lying between two star clusters, the tightly knit Pleiades and the V-shaped Hyades. A reddish star named Aldebaran is the brightest of the stars that make the V-shape of Taurus’s head. Over the course of the evening on January 21, a gibbous moon will pass between Jupiter and the Hyades with Aldebaran. The moon will come within about a degree of Jupiter, making for a nice photo-op.

If you own a telescope, point it toward Jupiter on January 21 to catch its moon Europa followed by its shadow pass in front of the surface of Jupiter. The satellite’s black shadow is much easier to spot in front of Jupiter than the brighter moon. It will take Europa’s shadow a couple hours to cross the planet’s surface. The shadow event begins around 9:30 p.m. Central Time.

Aldebaran is one of the six stars in the winter hexagon, pointing out six different constellations. Above Aldebaran in Taurus is Capella in Auriga, then move counterclockwise to Pollux in Gemini, then on to Procyon in Canis Minor, Sirius in Canis Major, and Rigel in Orion.

January's morning sky has two planets, Saturn and Venus, that can be found near the southern horizon. Saturn is in the constellation Libra, and the moon passes between Saturn and a fairly bright star Spica on January 6. Venus doesn't rise until almost dawn, shining at magnitude -3.9. Find a slim crescent moon less than three degrees from Venus on January 10. Venus begins the month in the constellation Ophiuchus but quickly moves into Sagittarius.

The Quadrantid meteor shower peaks overnight from January 3 to 4. A decent shower with up to 40 meteors an hour, the Quadrantids appear to emanate from the constellation Bootes, which rises in the northeast around midnight. A last quarter moon that rises at the same time as Bootes in January may dampen the display.  This month’s full moon, often called the Full Wolf Moon, occurs on January 26 at 8:38 p.m. PST.

A much-ballyhooed asteroid, 99942 Apohis, passes Earth on January 9 at a distance of 14 million kilometers. This is not a particularly close swipe at us, but Apophis returns in 2029 at which time it will reach a distance of 40,000 kilometers. Well inside the moon’s distance from Earth of 384,000 kilometers, Apophis will even come within range of Earth’s geosynchronous satellites. At 320 meters wide, Apophis would cause tsunamis if it hit water or devastate an area the size of Texas if it hit land. But fear not, it is not predicted to strike Earth at any point in time either now or in the future.

Another asteroid, discovered in 2012, will get just as close as Apophis will in 2029, only this asteroid will make its close encounter with us much sooner: in February 2013. Asteroid 2012 DA14 will pass about 40,000 kilometers from Earth at its closest approach at around 1:30 p.m. CST on February 15, 2013. At 45 meters across, Asteroid 2012 DA14 is smaller than Apophis and not classified by the International Astronomical Union as a “potentially hazardous asteroid”. An asteroid of 2012 DA14’s size would still level a city if it struck Earth, however it is also predicted to fly past us safely.

Photo credit: John Chumack.

Kelly Kizer Whitt loves clean, clear, and dark skies. Kelly studied English and Astronomy at the University of Wisconsin-Madison and worked for Astronomy magazine. She writes the SkyGuide for AstronomyToday.com. You can follow her on Twitter at twitter.com/Astronomommy.