Every week, SkyNews publishes a list of key events in the Canadian sky in This Week’s Sky. This series gives you all the latest news in Solar System movements, including where the planets are in our sky and Moon phases. From eclipses to meteor showers, This Week’s Sky keeps you updated on the best in upcoming astronomical highlights.
Wednesday, December 21 – Mercury at greatest eastern elongation (after sunset)
Mercury (orbit shown in red) will reach its widest separation of 20 degrees east of the Sun, and maximum visibility for its current evening apparition, on Wednesday, December 21. With Mercury positioned just below the tilted evening ecliptic (green line) in the southwestern sky, this appearance of the planet will be a relatively good one for both Northern and Southern Hemisphere observers. The optimal viewing times at mid-northern latitudes will be around 5:20 p.m. local time. Viewed in a telescope (inset) the planet will exhibit a waning, slightly gibbous phase. The much brighter planet Venus will shine to Mercury’s lower right (or celestial west).
Wednesday, December 21 – Northern winter solstice (at 21:48 GMT)
Winter in the Northern Hemisphere will officially commence on Wednesday, December 21 at 21:48 GMT, which converts to 4:48 p.m. EST and 1:48 p.m. PST. At that time, the Sun will reach the solstice — its southernmost declination for the year — resulting in the lowest elevation of the noonday Sun, the shortest amount of daylight of the year for the Northern Hemisphere, and the maximum daylight hours for the Southern Hemisphere. After the December solstice, the amount of daylight time will begin to increase for the Northern Hemisphere.
Thursday, December 22 – Ursids meteor shower peak (pre-dawn)
The annual Ursids meteor shower, produced by debris dropped by periodic comet 8P/Tuttle, runs from December 13 to 24. The short-duration shower will peak while Earth is traversing the densest part of the debris field on Thursday afternoon, December 22 in the Americas.
Since meteors require a dark sky, the best time to watch for them will be the hours before dawn on Thursday and again after dusk that night — but expect to catch fewer than the typical peak rate of five to 10 meteors per hour. True Ursids will appear to travel away from a position in the sky above Polaris in the Little Dipper (Ursa Minor), but the meteors can appear anywhere in the sky. This year’s shower peak will be moonless, allowing fainter meteors to be seen.
Friday, December 23 – New Moon (at 10:17 GMT)
The Moon will reach its new phase on Friday, December 23 at 5:17 a.m. EST, 2:17 a.m. PST, or 10:17 GMT. At that time our natural satellite will be located in Sagittarius, 4.5 degrees south of the Sun. While new, the Moon is traveling between Earth and the Sun. Since sunlight can only reach the far side of the Moon, and the Moon is in the same region of the sky as the Sun, the Moon becomes unobservable from anywhere on Earth for about a day (except during a solar eclipse). On the evenings following the new Moon phase, Earth’s planetary partner will return to shine in the western sky after sunset.
Saturday, December 24 – Crescent Moon meets Venus and Mercury (after sunset)
In the southwestern sky after sunset on Saturday, December 24, the very slim crescent of the young Moon will begin its monthly trip past the planets — shining several finger widths to the left (or five degrees to the celestial southeast) of Mercury and Venus. Mercury will be positioned to the upper left of 24 times brighter Venus, close enough for the two inner planets to share the view in binoculars (green circle) — but don’t aim any optical aids towards the western horizon until the Sun has completely set.
Sunday, December 25 – A Christmas star (late evening)
Sirius, the brightest star in Canis Major and in the entire sky (not counting the Sun), will appear above the southeastern horizon by 7:30 p.m. local time in late December. It is hard to miss Sirius once it clears the trees and rooftops. The star will climb to its highest point, in the lower part of the southern sky, shortly after midnight.
If you are walking through your darkened house in the middle of the night, Sirius might catch your eye out a window because it never climbs very high. Sirius is a hot, blue-white, A-class star located only 8.6 light-years from the Sun. Its extreme brightness and its low position in the sky combine to produce spectacular flashes of colour as it twinkles. A very large telescope may allow you to see Sirius B, a faint white dwarf companion located just 10 arcseconds east of Sirius.
Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the Universe together.