Mars at opposition on December 8, 2022 at 12:01 a.m. EST. | SkyNews
Mars at opposition on December 8, 2022 at 12:01 a.m. EST.

This Week’s Sky: December 5-11

The full Oak Moon occults Mars during the second week of December, while Algol’s visual brightness dims and re-brightens.

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 7 – Full Oak Moon occults Mars (at 11:08 p.m. EST)

Full Oak Moon occults Mars on December 7, 2022 at 10:28 p.m. EST. | SkyNews
Full Oak Moon occults Mars on December 7, 2022 at 10:28 p.m. EST. (Chris Vaughan, Starry Night Education)

The December full Moon will occur at 11:08 p.m. EST or 8:08 p.m. PST on Wednesday, December 7 in the Americas. That converts to 04:08 GMT on Thursday, December 8.

Traditionally known as the Oak Moon, Cold Moon, and Long Nights Moon, it always shines in or near the stars of Taurus and Gemini. The Ojibwe of the Great Lakes region call the December full Moon Manidoo Giizisoons, the “Little Spirit Moon.” For them, it is a time of purification and of healing of all creation. Since it is opposite the Sun on this day of the lunar month, the Moon is fully illuminated and rises at sunset and sets at sunrise. 

Full moons during the winter months reach as high in the sky at midnight as the summer noonday sun, and cast similar shadows. Since the planet Mars will also be opposite the Sun tonight, observers in northwestern Mexico, the Continental United States (except for southern and eastern states), all of Canada (except southwestern Nova Scotia), Greenland, Svalbard, western Europe, and the northern coast of Africa can watch the Moon pass in front of, or occult, Mars. 

The event can be observed with unaided eyes, binoculars, and telescopes. Exact times vary by location, so use an app like Starry Night to determine your own circumstances. In Toronto, Ontario, the leading edge of the Moon will cover Mars at 10:29 p.m. EST on Wednesday evening. Mars will reappear from behind the Moon’s opposite, southern limb at 11:17 p.m. EST. In Europe, the occultation will occur before dawn on Thursday morning. Start watching several minutes ahead of each time. 

Thursday, December 8 – Mars at opposition (all night)

Mars at opposition on December 8, 2022 at 12:01 a.m. EST. | SkyNews
Mars at opposition on December 8, 2022 at 12:01 a.m. EST. (Chris Vaughan, Starry Night Education)

Mars will officially reach opposition after midnight on Wednesday, December 7 in the Americas. On that night, the bright red planet and the full Moon will rise among the northerly horn stars of Taurus, the Bull at sunset, climb to their highest positions due south at midnight local time, and then set at sunrise. For observers located across most of North America, the full Moon will occult Mars on Wednesday evening. 

On opposition night, Mars will shine with a peak visual magnitude of -1.97. Although its distance from Earth of 51.05 million miles, 82.15 million km, 0.549 AU, or 4.72 light-minutes will be slightly farther than it was at its closest approach on November 30, Mars will still be an impressive sight in backyard telescopes — showing an apparent disk diameter of 17.05 arc-seconds (Jupiter’s disk spans about 42 arc-seconds). 

Mars’ Earth-facing hemisphere on December 7-8 will display its bright northern polar cap — visible as a small bright spot along the planet’s edge — the dark Tyrrhena Terra, Cimmeria Terra, and Sirenum Terra regions, and the lighter-toned Amazonis Planitia and Eylsium regions. After the lunar transit, the very dark, wedge-shaped Syrtis Major Planum region, the dark Tyrrhena Terra, and Sinus Sibaeus regions, and the lighter-toned Hellas Planitia region will all rotate into view. 

Mars oppositions occur approximately every 25.5 months. 

Friday, December 9 – Watch Algol fade (7:08 pm to 12:08 am EST)

Watch Algol fade on December 9, 2022 at 7:08 p.m. EST. | SkyNews
Watch Algol fade on December 9, 2022 at 7:08 p.m. EST. (Chris Vaughan, Starry Night Education)

Algol, also designated Beta Persei, is among the most easily observed variable stars for skywatchers. During a 10-hour period that repeats every two days, 20 hours, and 49 minutes, Algol’s visual brightness dims and re-brightens noticeably. This happens when a companion star, orbiting nearly edge-on to Earth, crosses in front of the much brighter main star, reducing the total light output we receive. 

Algol normally shines at magnitude 2.1, similar to the nearby star Almach (or Gamma Andromedae). But when fully dimmed, Algol’s magnitude 3.4 brightness is almost identical to Rho Persei (or Gorgonea Tertia, or ρ Per), the star that sits just two finger widths to Algol’s lower right (or 2.25 degrees to the celestial south). When Algol appears in the northeastern sky after dusk on Friday evening, December 9 in the Americas, it will be shining at its regular intensity. At 9:08 p.m. PST or 12:08 a.m. EST (on December 10), Algol will have faded to its minimum brightness. At that time it will sit nearly overhead. 

Algol’s changes can best be seen with unaided eyes and binoculars, which allow you to see its comparison stars at the same time. To find other opportunities to watch Algol fade, or to re-brighten, search the web for “minima of Algol” times. 

Saturday, December 10 – Gibbous Moon passes Pollux (all night)

Gibbous Moon passes Pollux on December 10, 2022 at 7:45 p.m. | SkyNews
Gibbous Moon passes Pollux on December 10, 2022 at 7:45 p.m.

In the eastern sky on Saturday evening, December 10, the waning gibbous Moon will shine several finger widths to the right (or several degrees to the celestial southwest) of the bright star Pollux in Gemini. Its fainter twin, the star Castor, will shine to their upper left. As the grouping crosses the sky during the night, the eastward orbital motion of the Moon will carry it closer to Pollux during the wee hours of Sunday. Meanwhile, the diurnal rotation of the sky will swing the Moon to the stars’ left. 

Tuesday, December 13 – Geminids meteor shower peak (overnight)

Geminids meteor shower peak on December 13, 2022 at midnight. | SkyNews
Geminids meteor shower peak on December 13, 2022 at midnight. (Chris Vaughan, Starry Night Education)

The Geminids meteor shower, usually one of the most spectacular showers of the year, runs from November 19 to December 24 annually. The number of meteors will gradually ramp up to a peak during the wee hours of December 14, and then decline rapidly on the following nights. 

Geminids meteors are often bright, intensely coloured, and slower-moving than average, because they are produced by sand-sized grains dropped by the asteroid designated 3200 Phaethon. 

In the Americas, expect to see the most Geminids beginning after dark on Tuesday evening, December 13, and continuing until dawn on Wednesday morning. True Geminids will appear to radiate from a position above the bright stars Castor and Pollux, but the meteors can appear anywhere in the sky. In years when the peak night sky is moonless, up to 120 meteors per hour are possible around 2 a.m. local time — when the sky overhead will be pointing toward the densest part of the debris field. 

In 2022, a waning gibbous Moon will rise in mid-evening, obscuring the fainter meteors. 

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 to tour the Universe together.