By Andy Veh, for the Redoubt Reporter
The starry sky is at its best with the most prominent stars high in the south — Blue Rigel and red Betelgeuse in Orion, Sirius beneath it, Procyon to its left, Pollux and Castor higher up, Capella almost in the zenith and Aldebaran and the Pleiades completing the splendor.
The Big Dipper starts out close on the northern horizon but Cassiopeia, Perseus and Andromeda are close to the zenith. In the west, Cygnus and Pegasus are about to set, while bright Vega, being circumpolar in Alaska, stays close to the horizon. Leo’s Regulus rises in the evening, trailing Gemini and Cancer low in the east.
Several planets are visible throughout January.
Uranus and Neptune can still be seen in the evening but they require finder charts. (I recommend Googling them.)
You can’t miss bright Jupiter as it rises in the east in the late evening, moving through the south during the night and setting in the west when school starts in the morning. This winter it appears between Leo and Virgo, halfway between these constellations’ brightest stars, Regulus and Spica.
Jupiter appears to be stationary this month. While it orbits on a nice, slightly elliptical orbit around our sun, we on Earth are starting to overtake it because we move along on a smaller, but still nice and slightly elliptical, orbit. So from our vantage point, Jupiter seems to slow down, come to a stop (on Jan. 8) and move backward — retrograde (which is an optical illusion) — through early May. When we finally pass the giant planet, it seems to stop again and regain its regular motion. The gibbous moon is near Jupiter on Jan. 27.
Mars rises longer after midnight but can be glimpsed before and during dawn. Follow the line of Regulus to the right, Jupiter in the middle and Spica to the left and you will find reddish Mars just east of Spica. Farther east are Saturn and Venus, but those two are close to the southern horizon before sunrise, which is also the only time they can be seen. The last quarter moon will be near Mars on Jan. 31.
Earth was at perihelion — its closest approach to the sun — on Jan. 2 (91.4 million miles) but only by 3 percent closer compared to its aphelion — its farthest distance from the sun — on July 4 (94.5 million miles). That means that about 6 percent more of the sun’s energy reaches Earth.
But that, in itself, is not the reason for the seasons. Perihelion and aphelion occur during the wrong seasons on the northern hemisphere. The maximum difference of 6 percent in solar radiation is way too small to account for the large temperature fluctuations between the seasons. And the varying distance doesn’t explain why and is not connected to how the lengths of the days and the altitudes of the sun above the horizon vary.
But due to the 23-degree tilt of Earth’s axis to its orbital plane, the length of day (which, at its extreme, is 70 percent shorter in winter than in summer — 5.7 hours compared to 19 hours) as well as the angle of the sun above the horizon are much more important. On the Kenai Peninsula, the noon sun is only at 7 degrees above the southern horizon in January versus 53 degrees in July — and these angles are important for how much energy is actually absorbed. Due to that large difference, any given ground surface area receives 85 percent less energy. Thus, seasons are solely caused by the tilt of Earth’s axis with respect to the sun.
In last month’s column I had mentioned that the waning crescent moon reaches Venus on Dec. 7. I had based that on the Astronomy magazine that I consult for my monthly columns, which stated that the moon passes 0.7 degrees north of Venus at noon EST (which is 8 a.m. AST). That Monday morning was clear and as I observed, and as other observers mentioned, what happened was more spectacular. Between 7 and 8 a.m. there was only the crescent moon in the southeast, but at 8 a.m. it was joined by Venus on its upper right, seemingly out of the blue (although the sky was still black).
From our vantage point in Alaska, Venus actually slipped behind our moon at 6:30 a.m., was occulted until 7:45 a.m., and then reappeared. Apparently I had not read Astronomy magazine carefully enough because it actually mentions this in the descriptive text. I apologize and I will be a more careful reader in the future.
Andy Veh is an associate professor of physics, math and astronomy at Kenai Peninsula College.