What’s up in the sky – December

By Fred Barrett

December is always a great month for stargazing but this year it offers a special treat – a total eclipse of the Moon!

The eclipse occurs during the night of December 20 / 21 and it has been three years since we’ve had a chance to see a lunar eclipse. During the partial stage of the eclipse you can see that the Earth’s shadow on the Moon is curved – visible proof that the Earth is round! Look around you as the eclipse progresses. As the Moon slowly becomes more shadowed, the night that was very bright earlier under the full Moon becomes darker and darker and more and more stars start to become visible. It gives me a strange feeling to sense the darkness growing around me. What was a light-filled, washed-out sky under a full Moon becomes a dark, starry expanse of glorious Milky Way! Watch as the shadow’s edge creeps from crater to mountain range as it makes its way across the Moon. The partial stage of the eclipse begins early morning on the 21st at 1:30AM (EST-Eastern Standard Time). Totality begins at 2:41AM and lasts until 3:53AM with midpoint at 3:17AM.

You may notice a reddish colour to the Moon’s surface during totality. Since there is no sunlight in the umbra, which is the Earth’s inner shadow, why isn’t the Moon completely black? Why does it have colour? What happens is that Earth’s atmosphere bends the light that grazes the edge of our globe sending it into the Earth’s shadow. The deeper the Moon is in the umbra, the darker it will appear. The Moon can vary from deep to light red to no colour at all. This is caused by the amount of dust in the atmosphere and is often provided by volcanic eruptions. The dust acts like a filter that favours light from the red end of the colour spectrum – it lets red light through to tinge the Moon. It will be interesting to see if atmospheric conditions around the Earth for this eclipse cause a deep red or colourless surface on the Moon.

Enjoy this eclipse because the next one for all of North America doesn’t happen until April 14 / 15, 2014. By the way, this month’s full Moon is called the COLD Moon; need I say more. Winter Solstice occurs at 6:38PM EDT about 15 hours after the eclipse. It marks the beginning of winter in the North and summer in the South. It is the longest night of the year for us.

An hour before sunrise (about 6AM) on December 3rd, have a look to the southeast. It will be difficult not to notice Venus which will be at its brightest and at its highest point in the sky this time around. It will shine at an astonishingly high magnitude of -4.9 (brightness increases as the magnitude number decreases and goes negative). By comparison, the brightest star in the sky, Sirius, is -1.46.

That’s not all, though. The crescent Moon, the bright star Spica (magnitude +1) and Saturn join with Venus to form a wavy line in the southeast. If you have a telescope, take a look at Saturn. Its rings, until recently, have been edge on to us and hard to see. They are coming more into view now and by the end of the month, will be quite a sight!

Jupiter is still bright in the south in the early evening (magnitude -2.4) but it’s getting smaller. A telescope will show two shadows on Jupiter from its moons Io and Europe starting at 5:45PM on the 25th and two shadows from Io and Ganymede starting at 8PM on the 26th.

Photo by Fred Barrett, taken a week or so ago through his 11" telescope using a Canon 20D DSLR. 1600ISO and 9 1/2 minute exposure.

The closest galaxy to our own Milky Way is the Andromeda Galaxy. It is now almost straight overhead throughout the night in the constellation Andromeda. The bottom right leg of Cassiopeia’s W points directly to it. Binoculars will be necessary, although on very clear dark nights, it can actually be seen by the naked eye. I have included a picture of this beautiful galaxy with this column to show that it is well worth looking for.

The beautiful winter constellation Orion rises above the horizon about 8PM in early December. The spectacular Orion Nebula can be seen below Orion’s belt. The constellation takes up a huge swath of sky! Above and to its left is the constellation Gemini with the twins Castor and Pollux at its head. I mention Gemini because this month on the evening of the 13th and the early morning of the 14th the great Geminid Meteor Shower occurs. This shower is often better than the Perseids in August. Dress warmly. It’s chilly out there, especially when standing still watching for meteors! You should expect about two meteors per minute when the shower ramps up in meteor numbers from 7PM on. The Moon is only at a quarter and sets around 1AM so the sky light conditions will be excellent. Note that the paths of the meteors radiate from Gemini in the East but the meteors can appear to start in any part of the sky.

If you have questions or suggestions, Fred Barrett may be contacted at cygnushill@hotmail.com

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, subscriptions for our very own excellent Canadian astronomy magazine, Sky News, are also available from RASC..