• Mel Hulbert

What’s in the Sky - December 2021

Moon Phase:

New Moon 4th

First Quarter 11th

Full Moon 19th

Last Quarter 27th

Summer Solstice: 22nd


Evening Sky

Mercury reappears in the constellation Sagittarius just above the southwest horizon after sunset on the 20th, and will steadily gain height through the remainder of the month. Venus is low in the western sky after sunset. The brilliantly shining planet is in the constellation Sagittarius and will slowly move closer to the horizon as the month progresses.

Jupiter is high in the western sky after sunset. The giant of the Solar System, starts the month in Capricornus and moves into Aquarius on the 15th.

Saturn is in the western evening sky in the constellation Capricornus.

Morning Sky

Mars makes a reappearance low in the morning sky during the first week of the month. Starting the month in Libra, the red planet moves into Scorpius on the 16th and into Ophiuchus on the 25th.

Worth a Look:

3rd: The waning crescent Moon is beside Mars in the early morning sky and a great opportunity for wide-field photographers.

6th & 7th: On the 6th, the waxing crescent Moon is below and to the south of Venus and on the 7th, the Moon is above and slightly to the west of the brilliantly shining planet. The crescent Moon and Venus together in the sky (and close to the horizon) are a wonderful target for wide-field photographers.

8th: The waxing crescent Moon is above Saturn in the western evening sky.

9th: The waxing crescent Moon is slightly to the west and above Jupiter.

27th: In the southwestern evening sky, Mercury and Venus will be side-by-side just above the horizon. Above and west of the two planets are Saturn and Jupiter and provides a great opportunity for wide-field photographers.

Solar Eclipse

4th: For those in Tasmania and southern Victoria, a partial eclipse will be visible. Parts of Antarctica and the South Pacific and South Atlantic Oceans will see a total solar eclipse. A solar eclipse occurs when the Moon passes between the Earth and the Sun. This three-body alignment is known as a syzygy.

A little quirk of nature means that the diameter of the Sun is 400 times greater than that of the Moon’s, but the Sun is on average 400 times farther away from the Earth, so both appear to have the same angular diameter (0.5°) in the sky. It’s this combination that allows us to see solar eclipses.

When the Moon is directly between the Earth and the Sun, it casts a conical shadow on the Earth. The darkest part of the shadow is called the umbra and no part of the Sun can be observed at totality from Earth. The lighter part of the shadow is known as the penumbra and the Moon will only partially cover the Sun. What we see will depend on where we are in the Moon’s shadow.

Standing at the point on the Earth where the umbra falls, results in observers seeing the disk of the Moon completely covering the disk of the Sun. This is called a Total Solar Eclipse. Observers only slightly removed from the umbra shadow would be in the penumbral shadow and see only part of the Sun’s disk covered by the Moon. This is called a Partial Solar Eclipse.

This partial eclipse for Tasmanians and southern Victorians will be low to the horizon. Caution: Special filters are required to view and image a solar eclipse and It is dangerous and harmful to your eyesight to watch a solar eclipse without the proper equipment. For those with solar filters, this is a great opportunity for telescopic and fixed telephoto lens imagers!

Timings for the eclipse in Hobart and Melbourne are listed in the table below.

Eclipse Hobart Melbourne Partial Begins 6:34pm* 6:53pm* Mid-Eclipse 7:06pm* 7:12pm* Partial Ends 7:37pm* 7:30pm*

* All times are in Australian Eastern Standard Time (AEST).

Meteor Shower

13th-14th: The Geminids are one of the best annual meteor showers. While most meteors showers originate from the debris left by comets, the Geminids are unusual in that they originate from 3200 Phaethon, an asteroid (or possible “rock-comet”) [1]. When the Earth passes through the trail of particles left by 3200 Phaethon, we see lots of meteors appearing to come from the one area of the sky. This is called the radiant and each shower is named after the constellation or bright star near which the radiant appears. In this case it’s the constellation of Gemini and the radiant is near the bright star Castor, one of the twins’ heads.

The best time to observe any meteor shower is after midnight, usually a few hours before dawn and in dark skies away from city lights if possible. The Geminids are active from the 4th to the 17th of December, with the peak on the morning of the 14th here in Australia. Predictions suggestion an hourly rate of 150 meteors, though keep in mind that this is a prediction and that activity can vary from year to year. With New Moon on the 15th, the early morning hours will be free from moonlight – perfect observing conditions! The Geminids often produce bright, medium speed (35km/s) and provides a good opportunity for both visual observers and widefield imagers. It will take patience and a wide angle lens with short continuous exposures to capture a meteor or two!

You can download a star map for December here.

Clear Skies!