What's Up in the Sky - December, 2009

Fred Barrett | Nov 26, 2009

\My highlight constellation for December is Cassiopeia and the area surrounding her. I say “her” because in Greek mythology Cassiopeia was the beautiful wife of Cepheus, king of Ethiopia and mother of Andromeda. The Queen in her vanity bragged that she and Andromeda were more beautiful than the sea-nymphs, the Nereids. The nymphs, rather insulted wanted revenge and complained to Poseidon, god of the sea. He threatened to send a flood and a sea monster, Cetus to ravage the King’s seacoast. An Oracle foretold that only by sacrificing their daughter Andromeda would Poseidon be appeased. The king chained her to a sea cliff and the hero Perseus saw her as he was travelling along the coast. He saw her beauty and fell immediately in love with her (what else?). After learning what had gone before, he agreed to rescue her if he could marry her. Well, he saves her in the nick of time in one of the most famous rescue stories in history. The gods were so happy that they raised all the characters to the heavens but an indignity was done upon Cassiopeia. She was condemned to circle the celestial pole on her throne and that means she spends half of every night upside down.

The Milky Way crosses Cassiopeia which makes it fairly easy to find. It’s high in the Northeast in the evening at this time of the year. Just follow the nebulosity of the Milky Way up from the horizon and you will encounter a W or M shape near the Zenith or highest point in the sky. The whole area is very rich in objects that can be viewed easily with binoculars and even by naked eye. Using figure 1 as a guide, one of the most interesting objects to look for is the sword handle of Perseus. It contains two easily seen open clusters of stars. The galaxy M31 can be seen by eye on a clear, dark night using averted vision. It is below Cassiopeia, down in the left corner of figure 1. Averted vision is a technique for bringing the most sensitive portions of your eye into use. These are the areas around, but not at the centre of the eye. To use this technique, look a little off to one side of an object and not directly at it.

There are several open clusters that are easy to see with binoculars - M103, NGC663, M52 and NGC7789. NGC7789 is known as the White Rose cluster because the loops of stars and dark dust lanes look like the swirling pattern of rose petals. Look for M76, also known as the Little Dumbbell nebula and NGC457, the Owl nebula. Both require a modest telescope to see.

In figure 1 small circles with three or more numbers denote deep sky objects that can be hunted with binoculars or a telescope. Give it a try and Good hunting!

In the night sky, 10 degrees is about the width of your fist at arm’s length. One degree is made of 60 minutes and one minute is made up of 60 arc seconds. So, one second in width is a very small size.

The Moon – December has two full Moons, December 2 and December 31. This event, which occurs every three years or so, is mistakenly called a Blue Moon because of an error that was made in the 1946 issue of the astronomy magazine Sky & Telescope. It got reported on a national radio program, eventually found its way into the game of Trivial Pursuit and thus became “fact” and an urban legend. An actual Blue Moon is the result of smoke and dust from fires or volcanoes. The moon and the sun can take on a blue tint. It is very rare. Although it is difficult to tell by eye, on December 31 the full moon is the largest moon of 2009.

The Planets: Mercury – You will need binoculars to see Mercury low in the Southwest in early December but by mid-month, it should be a naked eye object about six degrees above the horizon after sunset. It will fade from view by month’s end.

Venus – It rises shortly before the Sun as December begins but is lost in the sunrise after only a few days.

Mars – Rises a few hours after the sun in early December but by the end of the month appears about three hours after sunset. On December 18 use binoculars to see Mercury 6 degrees to the lower right of the crescent Moon in the Southwest after sunset. The earth is catching up with Mars in its orbit and therefore its Eastern movement in the sky is slowing and will eventually stop on December 21. On that date it starts moving Westward (retrograde) in the sky. Mars is getting larger too as earth gets nearer but you will still need binoculars or a telescope to see its 12.7 arc second diameter. Earth passes Mars every 26 months. Don’t fall for that e-mail that goes around when this opposition occurs. It’s the one that exclaims that Mars will be as large as the Moon – in a telescope maybe! This opposition occurs January 9, 2010 and Mars will be only 14 arc seconds in diameter.

Jupiter – You can see Jupiter in the high south south-west as the sun sets. Jupiter sets by about 8PM by month’s end.

Saturn – At the start of December, Saturn rises about 1:30AM. By December 31, it rises around 11:30PM. It is highest just before the sun comes up. Its rings are becoming more obvious as their tilt increases from 4.3 degrees to 4.9 degrees at the end of December. You will need a telescope to see the rings but the planet itself will be very bright in the sky.

Meteors – The Geminids - This is one of the finest meteor showers of the year and a personal favourite. The radiant or the spot in the sky from which the meteors appear to originate, is just North of the star Castor in the constellation Gemini and Gemini will be about 30 degrees above the Eastern horizon.

The shower occurs on the night of December 13/14. This year is a special treat. The Moon is new so it won’t be in the sky acting like a huge spotlight! The predicted peak is midnight, with hourly rates increasing from early evening until then. The ZHR (Zenith Hourly Rate) is expected to peak at 120. Get out there and bundle up well against the chill.

Special dates:

- December 7 is the earliest sunset of the year.

- December 21 is the shortest day of the year (Winter Solstice) in the Northern Hemisphere. Winter begins at 12:47PM EST when the Sun reaches its southern most point in the Northern Hemisphere sky which is directly  over the Tropic of Capricorn in the southern hemisphere (Summer Solstice  begins in the Southern Hemisphere).

The Sharbot Lake Pharmacy is expecting a shipment of The Beginner’s Observing Guide by Leo Enright in time for Christmas.

Don’t forget that we have an excellent Canadian astronomy magazine, SKY NEWS. You can arrange for a copy by contacting the Royal Astronomical Society of Canada at www.rasc.ca/publications.

The Beginner’s Observer’s Guide by Leo Enright is available at the Sharbot Lake Pharmacy or by contacting the Royal Astronomical Society of Canada www.rasc.ca/publications.