Sky at a Glance December 9 – 16

Photo of the constellation Gemini

This Week’s Sky at a Glance, December 9 – 16 ~by Curt Nason

Perhaps the year’s best meteor shower radiates from near the star Castor in Gemini this week. Under ideal conditions the Geminids can average two shooting stars per minute, but don’t expect to see anywhere near that number. Be very happy if you see a couple dozen per hour. With Gemini rising soon after an early sunset and riding high just after midnight, convenient evening viewing is rewarded more often than for the showers from Perseus and Leo, which rise much later on their peak nights. Geminids are relatively slow and easier to catch with the eye, and they often have a golden glow.

This year the shower peaks around 3 a.m. on December 14, making that morning and the previous evening the best time to watch. As a bonus for evening observers the moon doesn’t rise until 4 a.m., and its waning crescent phase will not wash out the sky significantly for morning viewers. Dress very warmly, get comfortable in a reclining position, face an unobstructed patch of sky toward the north or south away from artificial lighting, and hope for a cloudless evening. Viewing on the evenings before and after could also be worthwhile if the weather forecast isn’t promising for December 13.

The parent “comet” for the Geminids is actually the asteroid 3200 Phaethon, which was discovered in 1983. It orbits the Sun in a little more than 17 months, crossing the orbits of Mars, Earth, Venus and Mercury. At perihelion its temperature can exceed 600C, which can cause its carbon-water material to break down and release the dust particles that give us meteors when they burn up in our atmosphere. On December 16 Phaethon passes within 10 million kilometres of Earth and can be seen moving against the background stars with a medium-size telescope.

This Week in the Solar System

Saturday’s sunrise in Moncton is at 7:49 am and sunset will occur at 4:33 pm, giving 8 hours, 44 minutes of daylight (7:51 am and 4:41 pm in Saint John). Next Saturday the Sun will rise at 7:55 am and set at 4:34 pm, giving 8 hours, 39 minutes of daylight (7:57 am and 4:42 pm in Saint John).

The Moon is at third quarter on Sunday, and passes above Mars and Jupiter on Wednesday and Thursday mornings, respectively. Mercury is at inferior conjunction on Tuesday, moving into the morning sky later in the month. Saturn sets just 35 minutes after sunset midweek, while Mars is moving rapidly toward Jupiter in the morning sky. (Spoiler alert: It catches up on January 7.) Venus is heading sunward, reaching superior conjunction on January 9.

The William Brydone Jack Astronomy Club meets at the UNB Forestry / Earth Sciences Building in Fredericton on Tuesday at 7pm. All are welcome. That same evening, an uncertified lunatic gives a presentation on the Moon at the Mapleton Park Rotary Lodge in Moncton.

Questions? Contact Curt Nason.

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