What's Up in the Night Sky

February 2018 - Vol. 22, No. 2

This Month's Night Sky - NOTE: The next paragraph describes the sky as it appears at 10 pm EST (11 pm EDT) near mid- month. The sky also looks this way at 11 pm EST (midnight EDT) during the beginning of the month and at 9 pm EST (10 pm EDT) by month's end.

The "Winter Triangle" asterism shines high overhead. It appears as an inverted triangle formed by three bright stars: Sirius (Canis Major) below, reddish Betelgeuse (Orion) upper right, and Procyon (Canis Minor). Betelgeuse is also the upper left member of my favorite asterism, hour-glass shaped Orion. If you have a clear sky, look for a hazy patch of light below Orion's middle "belt" star. That is M42, the Great Orion Nebula, the site of intense star formation. (At least it was some 1,600 years ago since it took that long for the light to reach you!) Other bright stars of interest are Rigel, the bottom left star in Orion, Aldebaran (Taurus) in the SW, Castor and Pollux (the Gemini twins) high above the winter triangle and orangish Arcturus (Bootes) right on the E horizon. The "Big Dipper" of Ursa Major stands majestically high in the N.

MERCURY unfavorably placed for northern observers and seen with difficulty from the south in the morning sky, superior conjunction on the 17th. VENUS may be observed in the night sky in the last few days of the month. MARS visible in the morning, rising at 3 am by month's end. JUPITER in Libra rises earlier every morning. SATURN in Sagittarius rises before the Sun. URANUS in the evening sky. NEPTUNE approaching conjunction next month would be a difficult target, much better to view closer to autumnal equinox.

Review how to determine Angular Measurement.

Calendar of Events

NOTE: For those observers not in the ET zone, convert the calendar times to your zone's time by subtracting one hour for CT, two for MT and three for PT. Don't forget to adjust for Daylight Savings Time when necessary by subtracting one hour from your planisphere's time. Dawn and dusk times must also be corrected. See your local newspaper, TV news, or cable TV's Weather Channel for sunrise and sunset times or check with the U.S. Naval observatory. Unfortunately some of these events may occur during daylight hours in your area.

DATE	EVENT
01	Regulus 1.0 deg S. of Moon, occultation from Scandinavia, N. Greenland, Svalbard, parts of Russia, China, Alaska and Japan.
02	Look W from a dark location, at about an hour after sunset, to view zodiacal light. ("Zodiacal light" is a vertical band of white light believed to be sunlight reflected from meteoroids found in the plane of the ecliptic, the apparent "path" of the Sun, Moon and Planets as they travel across our sky.) It will appear to be a very large, but very dim, pyramid of of white light, "leaning" to the left. This effect may be visible for the next two weeks on dark nights.
07	Jupiter 4 deg S. of Moon.
09	Mars 4 deg S. of Moon. Vesta .9 deg N. of Moon, occultation from Antarctica.
11	Moon at apogee. Saturn 2 deg S. of Moon.
15	Partial Solar Eclipse best seen from An tar tic a and S South America.
17	Mercury at superior conjunction.
23	Aldebaran .7 deg S. of Moon, occultation from Bermuda. NE North America, Greenland, Europe, Russia, Kazakhstan,, W Mongolia, and NE China.
27	Moon at perigee.

Lunar Almanac for February 2018

Phases of the Moon	Phase and Date(s)	Best viewed before local midnight
	New 15	Deep Space Objects
	1st. Qtr 23	Planets & Moon
	Full Mar 2	Moon
	Last Qtr 07	Deep Space & Planets

Topic of the month: Gemini

Gemini, the celestial twins Among the brightest stars in the winter sky, Gemini has long been associated with twins or brothers as the constellation may appear to some as a pair of figures, as suggested by the star chart accompanying this article. Two bright stars, Castor, or Alpha Geminoris(1.6 mag) is a multiple star system with 6 known members, the brightest pair orbiting at a distance of 90 au. Their period or mutual orbit is about 445 years. In contrast, Beta Geminoris, or Pollux shines at 1.1 magnitude and is in fact, the brightest star of the constellation. Castor and Pollux in mythology were the sons of Leda. A myriad of stories revolve around these two stars. Most cultures seemed to associate them with brothers or twins, called "Dioscuri"or "sons of Zeus" in Rome. They have been associated with Adam and Eve, Romulus and Remus, called the patron saint of sailors and somehow related to St. Elmo's fire, the eerie blue glow surrounding the top of the mast of the ship during a lightning storm. The celestial twins were minted on coins by the Greeks and Romans.

Gamma Geminoris, also known as "Alhena" is a blue star calculated to be 109.3 light years away in 2007. The name Alhena is generally agreed upon, the word itself meaning "brand mark" such as those used on camels in the middle east. (Al-Han'ah) The star is located at the foot of the Pollux twin. At magnitude 1.9 it is almost as bright as Castor. It is considered to be the 44th brightest star in the sky today and easily seen without optical aide.

Delta Geminorum, popularly called "Wasat" (mag 3.5), is located quite nearly on the ecliptic, a mere 2" away. Wasat means middle, perhaps a reference to the ecliptic or the central of the Gemini constellation. In China the star was called "Ta Tsun", or Great Wine-jar. Wasat is a part of history as Pluto was discovered in a photo plate containing this star. It is a double star, a 3.5 white star with an 8.1 orange companion star 6.3"away. This star is best in moderate sized telescopes and has been used to test the atmosphere conditions by amateurs.

Epsilon Geminoris (Mebsuta) is a yellow star shining at mag 3.1. It is about 840 light-years from Earth. This star has an optical companion (9.6 mag) that can be seen in binoculars. Zeta Geminoris (Mekbuda) is a Cepheid variable star with a period of 10.2 days (4.2 - 3.6 mag) about 1200 light-years from Earth. This star has 3 known companions. Eta Geminoris (Propus) is a triple star system requiring at least 12" aperture to detect one 6.5 companion. It is an M class star whose orangish hue may be visible in binoculars. It is 384.63 light-years away. This star is also variable with a period of 234 days. (3.9 - 3. 1 mag) In keeping with the star's location near the ecliptic, the planet Uranus was close to this star when discovered by William Herschel.

More information on Gemini can be found at found at: http://www.astras-stargate.com/dec16-up.html. Learn more about Castor and Pollux and locate deep-sky objects in the constellation.

--See You Under the Stars!
Astra for Astra's Almanac