This month, Mars remains in the southwest at dusk this month as it moves through Capricornus. Mars continues to fade a little each night as Earth continues to leave it farther behind.
Jupiter is now high in the south at dawn; it is the brightest thing there.
Venus begins to emerge from the Sun’s glare late this month. Can you spot it low in the southwest at dusk by New Year’s Eve?
Saturn begins to emerge into the morning sky by mid-month. Look low in the southeast at dawn.
In December, the Big Dipper is below the horizon at dusk. As the Big Dipper sets, though, Cassiopeia is high above the North Star. This is a pattern of five stars in a distinct M or W shape. Look for Cassiopeia high in the north on fall and winter evenings.
The Summer Triangle sets in the west. Watch for the Great Square of Pegasus almost overhead at dusk now and in the west by Christmas. Taurus, the Bull rises in the east. Look for the Pleiades star cluster above reddish Aldebaran. Dazzling Orion, the Hunter rises shortly after dusk (by month’s end, it is already up at dusk). As Orion enters the evening sky, we transition from the relatively dim evening skies of autumn to the brilliant stars of winter. We are beginning to face away from the center of the galaxy, looking at stars behind us in our own part (the Orion Spur) of our galaxy.
Moon Phases in December 2014:
Full: December 6, 11:26 am
Last Quarter: December 14, 11:53 am
New: December 22, 12:35 am
1st Quarter: December 28, 5:32 pm
At 10:03 pm on Sunday, December 21, the Sun is directly overhead at the Tropic of Capricorn, the farthest point south where this is possible. This puts the Sun as low as possible in our sky, and marks the winter solstice. In the Southern Hemisphere, the Sun is as high as possible in the sky—this is the summer solstice for them.
Although the winter solstice is the shortest day, the earliest sunset occurred on about December 2, and the latest sunrise will occur January 10.
That’s because the Earth speeds up on its orbit as it approaches perihelion (closest approach to the Sun) next month. This acceleration shifts sunrise, local noon, and sunset slightly later each day this month and next. The effect is smaller than that of the Sun taking a lower path across the sky, which normally dominates in causing earlier sunsets and later sunrises. But the Sun’s apparent path varies very little near the solstice itself, allowing the secondary effect of the Earth approaching the Sun to predominate. For most people, then, (those who witness sunset but sleep through sunrise), days will seem to lengthen throughout December, although they don’t really begin lengthening until December 21.
The Geminid Meteor Shower peaks this month, as it does every December. Along with the Perseids in August, the Geminids are one of the two most reliable meteor showers, producing on average about 100 meteors per hour.
The Geminids are unique among meteor showers because they are associated not with a comet but with an asteroid, 3200 Phaethon. This means that with Geminids, we see significant activity much earlier in the night than with other showers. Most meteor showers peak in the hours immediately before dawn. This is because what plows through the debris field is the leading edge of the Earth, and that’s the side going from night into day. Since Phaethon is an asteroid, however, debris along its orbital path forms a shallower angle to Earth’s orbital path, meaning that we begin to face into the debris field as early as 9 or 10 pm. Meteors will seem to ‘radiate’ from the constellation Gemini, hence the name of the shower. However, they may appear anywhere in the sky.
As always, you see more meteors the farther you are from big city lights which hide dimmer ones. Our George Observatory will be open from 5pm to midnight Saturday night, December 13 for observing this meteor shower. Midnight is about when the Moon, approaching last quarter phase, will rise.
Click here for the Burke baker Planetarium Schedule.
On most clear Saturday nights at the George Observatory, you can hear me do live star tours on the observation deck with a green laser pointer. If you’re there, listen for my announcement.