Night Lights: Leap at the chance for stargazing this month

sky_in_February_2016

Graphic courtesy of Andy Veh

By Andy Veh, for the Redoubt Reporter

Late in the evening, winter constellations such as Taurus, Pegasus and Andromeda have set already. But others show their glory, such as Orion with its seven bright stars — among them red Betelgeuse and blue Rigel — Auriga with yellow Capella, Gemini with Castor and Pollux, and Procyon and Sirius in Canis Minor and Major, both arching toward the horizon from the Twins.

Lately, I have enjoyed seeing the brightest star, Sirius, above the southern horizon in the evening. Leo, a harbinger of spring, with Regulus in its front paw, appears high in the south. The Big Dipper is now virtually overhead. Blue Vega and Cygnus with Deneb are just above the Little Dipper. Polaris, as always, is 60 degrees above the northern horizon. And in the east, Bootes appears with red Arcturus.

Uranus can still be seen in the evening, but it requires a finder chart (I recommend Googling one). The sun has finally moved in on slow-orbiting Neptune (of course, the sun doesn’t move, Earth’s orbit just gives it that impression), so that the planet is no longer visible until the fall.

You can’t miss bright Jupiter as it rises in the east in the evening, moving through the south throughout the night and setting in the west in the morning. This winter it appears between Leo and Virgo, halfway between these constellations’ brightest stars, Regulus and Spica.

Mars rises around 2 a.m. and Saturn around 5 a.m. Try this before and during dawn — from left to right (east to west) along the southern horizon, stretch a line with almost equal distances from Saturn to reddish Mars to Virgo’s Spica to very bright Jupiter to Leo’s Regulus (four of these five are similar in brightness, with Jupiter being much brighter).

The waning crescent moon appears left of Saturn on Feb. 4. Three weeks later the full moon will be near Regulus on Feb. 22 and near Jupiter on Feb. 23. The gibbous moon will be near Spica on Feb. 26 and 27, the last quarter moon will be near Mars on Feb. 29, and near Saturn on March 1 and 2. That motion through consecutive days shows that the moon is orbiting west to east (counterclockwise), and that its phases are linked to the position in its orbit. The latter (phases) depends on how much sunlight the moon reflects to Earth in the different positions in its orbit. The former (orbit) is an example of almost all motions in the solar system.

Virtually all bodies — planets, moons (with the prominent exception of Neptune’s Triton) and asteroids, orbit counterclockwise and rotate west to east (with the prominent exception of Venus). Since Earth rotates west to east, we get the illusion that, throughout the day, the sun and, throughout the night, the stars move east to west.

While Venus, Mercury, the waning crescent moon and even Pluto are really close to each other around Feb. 6, none of them can be observed from Alaska because they are too close to the horizon before and during dawn. That’s due to the ecliptic making a really shallow angle with the horizon in Alaska. Planets that appear close to the sun are also close to the horizon. That’s also the reason why we enjoy quite a bit of dawn and dusk. At latitudes near the equator, in California, Texas and Florida, the ecliptic is steeper, and planets close to the sun are higher above the horizon, but they have much shorter dawn and dusk.

We’re in a leap year in 2016. An Earth year is based on Earth appearing in the same spot in its orbit. That time, however, is not an integer multiple of an Earth day, but instead lasts 365.2425 days. The decimals are close to one quarter and can be added up to one full day after four years, so we have a leap day (Feb. 29) every four years. (The Summer Olympics are always scheduled in leap years, by the way.)

Notice that this computation of the Gregorian calendar over accounts 0.0075 days every year, so once in a blue moon a leap year needs be skipped, specifically about three times in 400 years (since 0.0075 times 400 equals 3). Thus, leap years will still be every four years — 2016, 2020, 2024, etc. — but 2100 will be skipped. So, a very rare event should be referred to as “once in a skipped leap year,” instead of “once in a blue moon.”

I’ll be offering free astronomy classes at Kenai Peninsula College’s Kenai River Campus through Soldotna Community Schools from 7 to 9 p.m. Tuesdays, Feb. 9, Feb. 16 (my birthday) and Feb. 23, intending to cover observation techniques and doing outside observations, and explaining Special Relativity — in one evening! — on March 1. The classes are free and open to the public.

Andy Veh is an associate professor of physics, math and astronomy at Kenai Peninsula College.

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Filed under astronomy, Night Lights

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