Sky at a Glance December 15 – 22

Photo showing the location of the eclipsing binary star(s) Algol in the constellation Perseus.

This Week’s Sky at a Glance, December 15 – 22 ~by Curt Nason

Evening stargazing can be tricky this time of year with all the festive lights, especially if you have a neighbourhood Griswald. You can make the best of it by finding a darker location or waiting until most people have turned their lights off. Occasionally I make the best of it by targeting some distant colourful outdoor display with binoculars or a telescope.

If you happen to be out, try identifying a few constellations. In the northeast there is pentagonal Auriga the Charioteer, with bright Capella the Goat Star at one corner. To the right is the V-shaped face of Taurus the Bull, with the dipper-like star cluster of the Pleiades marking its shoulder. Orion and Gemini follow below Taurus and Auriga. Above Auriga is Perseus, seemingly standing on the bull’s back. It is here a patient stargazer can watch a marvel of the night sky.

In mythology, Perseus beheaded Medusa to seek revenge on tormentors by turning them to stone. The second brightest star in the constellation Perseus represents the evil eye of Medusa and it is called Algol, the ghoul or demon. There is a reason for this name. Every three days, minus about three hours, this star slowly dims by a factor of three and regains brightness over several hours. Algol is an eclipsing binary, two stars orbiting each other closely and aligned to our line of sight. When the smaller, dimmer star passes in front of the brighter one we can see their combined-light diminish and recover. By comparing it with nearby stars of similar brightness you might notice Algol getting brighter. Our next evening opportunity to watch this is around 10 pm Christmas night.

This Week in the Solar System

Saturday’s sunrise in Moncton is at 7:54 am and sunset will occur at 4:34 pm, giving 8 hours, 40 minutes of daylight (7:56 am and 4:42 pm in Saint John). Next Saturday the Sun will rise at 7:58 am and set at 4:36 pm, giving 8 hours, 38 minutes of daylight (8:00 am and 4:44 pm in Saint John). The Winter Solstice occurs on December 21 at 6:23 pm, the day of minimum sunlight but giving lots of time for stargazing.

The Moon is at first quarter this Saturday and full next Saturday, the Long Night Moon or the Mi’mgaw Chief Moon. Mercury is at greatest elongation this Saturday, rising nearly two hours before the Sun and two hours after Venus. Jupiter climbs to within one degree of Mercury by Thursday, and next Saturday they rise together with brighter Jupiter on the right. Mars is at its highest in the south at 6 pm, but Saturn is too low in the west at sunset for observing. Comet 46P/Wirtanen passes between the V-shaped Hyades star cluster and the Pleiades star cluster this weekend as it moves to within 11.5 million kilometres of Earth. It is seen best with binoculars, resembling a hazy thumbprint the size of the Moon or larger. You might also catch a few late meteors from the Geminid shower this weekend.

Questions? Contact Curt Nason.

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