SKY THIS MONTH

By P. Naik

 The chart shows the night sky over Shillong during the month of January 2009 at 7.00 p.m. Shillong being at 25.5oN latitude we see mostly northern constellations. The E-W line shows the celestial equator and the line cutting it shows the zodiac line or the sun’s apparent path.

The capital letters indicate the name of constellations and the other letters indicate the prominent stars. Planet Venus is visible over the western sky in the evening only.

Planet Jupiter is clearly visible most of the night. Planet Uranus and Neptune are not visible to naked eye but through telescope only.

The prominent constellations visible are Eridanus, Cetus, Aquarius, Piscis Austrinus, Pisces, Canis major, Gemini, Taurus, Aries,Draco,Cancer, Orion, Perseus, Andromeda, Cassiopeia, Ursa major, Ursa minor, Auriga, Pegasus, and Cygnus.

The constellation of the month is Cassiopeia which is in the shape of M or inverted W The constellation is named after Cassiopeia, a queen in Greek mythology. Cassiopeia was the wife of King Cepheus, and became jealous of the beauty of their daughter Andromeda was very beautiful.

When she boasted for her beauty, Poseidon, the sea god, sentenced Andromeda to be tied to a rock with a sea monster awaiting her.

The hero Perseus defeated the monster, and claimed her as his wife, but Cepheus and Cassiopea preferred her to marry another man, Phineus.

In the ensuing battle, Perseus slew his opposers, and Cepheus and Cassiopeia were placed next to each other among the stars by Poseidon, Cassiopeia being placed upside down for half the year because of her vanity. In another tradition, Cassiopeia was a consort of the god Zeus and had a son named Atymnios with whom two men fell in love. Cassiopeia was hung upside down in a chair in the stars upon her death.

Two of the main stars in Cassiopeia, á, Schedir, and ã, Tsih, are variable (about mag 2·16 and 1·6-2·9, respectively).

The latter has a mag 8·2 companion.

Of the remaining three stars making up the famous ‘W’. â, Chaph, is a mag 2·26, F2 type, ä, Ruchbah, is a mag 2·67 A5 (probably an eclipsing variable with a 759-day period) and å, Cassiopeiae, is a mag 3·3.

All but the last are less than 150 light years distant, but å is 500 light years away with an absolute mag of -2·7. The southern half of the constellation contains part of the Milky Way and many open clusters populate the region including M52 and M103. Cassiopeia lies opposite Ursa Major across the celestial north pole.

The special events during the month are a total lunar eclipse on 10th ( visible over shilling during the early night hours) and winter solstice on 21st..

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