December 2021 Skies

December 2021 Skies

Summer starts in Australia and New Zealand on December 1, and the nights are most definitely getting shorter. Both countries use the meteorological definitions of the seasons. Other countries use the astronomical definitions which relate to equinoxes and solstices.

Key points this month are not to miss out on the Geminids Meteor Shower and checking out 4 bright planets in the evening sky throughout the month.

December is well known to those interested in the night sky due to the solstice, which this year comes at 2:59am AEDT Wednesday December 22nd. Virtually every culture has celebrated the solstice as a seasonal “turning point. in the North it is a sign that brighter, longer days lie ahead and for the South that the nights will start to get longer.

Wurdi Youang is a stone arrangement site in Wathaurong country in Victoria dates back some 11,000 years ago. The stones were positioned to track the winter and summer solstice with three stones pointing to the summer equinox. Various research over the years has removed the possibility that this formation could have been caused by nature but rather that it portrays a culture that was well-attuned to the timings of the cosmos and could utilize its movements to aid tribal living.

This month is also known for the annual Geminid meteor shower, which peaks on Saturday, December 14th. Ordinarily astronomers can count on the Geminids to give us a pretty good show, maybe one meteor per minute from a really dark location. But this year the Moon is nearly full, so its light will wash out the faintest Geminids but it is still worth going out to check in the early hours of a December 14.

Constellations

During summer the bright centre of the Milky Way is mostly below the western horizon by now This means we need to look to the south and east to see the cool stuff during the short warm summer evenings.

This is the time to check out the constellation of Orion – also known to us down under as ‘The Saucepan’ with its striking patterns of stars it makes for easy stargazing.

The Pleiades, Taurus, Orion, and his hunting dogs Canis Major and Canis Minor make their welcome return to the evening skies, spawning all manner of mythological tales. Sirius reminds us that it is the brightest star in the night sky, as it marks the collar of Canis Major, the ‘big dog’, while Orion has to negotiate with Taurus, the Bull, if he ever wants to make it with the Seven Sisters by Greek and roman mythology.

In many cultures the Pleiades are seen as seven sisters being pursued, usually by a man or beast. With indigenous Australian’s this is no different. The Warlpiri tribe of central Australia, see the the group of stars as the Napaljarri sisters from one skin group being chased by the Jakamarra man from a different skin group trying to take a wife, forbidden by tribal law.

In many other Australian indigenous cultures, the Pleiades are a group of young girls, and are often associated with sacred women’s ceremonies and stories. The Pleiades are also important as an element of Aboriginal calendars and astronomy, and for several groups their first rising at dawn marks the start of winter.

Western commonalities like The Pleiades don’t stop there. While the indigenous folks look for meaning between the stars in the dark, western cultures look for it in the stars themselves. We do share a common comfort that the stars above us are our loved ones watching peacefully over us.

Venus, Saturn and Jupiter continue their impressive nightly display lined up in the western evening sky.

Since Daylight Saving is in place in New South Wales, Victoria, South Australia, Tasmania, the Australian Capital Territory and Norfolk Island, all times this Month are in AEDT (Australian Eastern Daylight Time)

The Moon this Month

(All times are in Australian Eastern Daylight Time)

New Moon:                    06:00 pm December 4th

First Quarter:                 Noon December 11th

Full Moon:                      03:00 pm December 19th

Last quarter:                  Noon December 27th

At 8pm on December 4, the Moon will be at Perigee, the closest it gets to the Earth each month. This month will be a mere 356,794 km away. On the 18th at noon, the Moon will be at apogee, its furthest point from Earth this Month at 406,320 km.

Co-incident with the New Moon there is a solar eclipse this month on 4 December, but its path is so far out there that we won’t be able to see it. People in the far southeast of Australia such as Tasmania will get a glimpse of a partial eclipse, but only barely and it will be difficult to see, and you will need to be using correct protective eclipse glasses or appropriate filters to see the small bite taken out of the Sun. It is never safe to look directly at the Sun.

Summer Solstice

The ancient Celts celebrated the summer and winter solstice as the time when the day length started to change. The December solstice occurs at 02:59 AEDT on December 22. At this time the South Pole of the earth will be tilted toward the Sun. The Sun will have reached its southernmost position in the sky and will be directly over the Tropic of Capricorn at 23.44 degrees south latitude. This is the first day of winter (winter solstice) in the Northern Hemisphere and the first day of astronomical summer (summer solstice) in some countries in the Southern Hemisphere

If you have been able to regularly watch the sunrise or sunset (a bit difficult of late in the eastern states with all the rain and cloud)  you may have noticed that it rises and sets in a different place each day relative to the horizon. Due to a combination of the Earth’s tilt and orbit, over the course of a year the place against the horizon where the Sun rises and sets moves north, and then south, and back again, and the days where it reaches its maximum and turns around are the solstices. The word ‘solstice’ comes from ancient Latin – sol: sun, sistere: stand still.

On 22 December the Sun has reached its most northern location. Following this, it will then appear to move south a little more each day. It can be a fun little project over the next few months to make a note of where the Sun sets. You don’t have to do it every day, but try it maybe once a week, note where the Sun has set against the horizon and watch it move week after week. You should catch the last of its northern motion before the turning point on the 21st and the subsequent southern motion.

The December solstice is also the day of the year with the most amount of daylight for those in the southern hemisphere, and from here on out the days will get shorter. Note that this doesn’t mean that sunset will be earlier – in fact, it’s still getting later as summer progresses, but the later sunrises each day will start to shave time off the length of the day, making this a maximum length day.

Planets in December

This month’s fun fact about the planets:

Venus

Venus is the second planet from the Sun and is Earth’s closest planetary neighbour. It’s one of the four inner rocky planets, and it’s often called Earth’s twin because it’s similar in size and density. These are not identical twins, however – there are radical differences between the two worlds.

Venus has a thick, toxic atmosphere filled with carbon dioxide and it’s perpetually shrouded in thick, yellowish clouds of sulfuric acid that trap heat, causing a runaway greenhouse effect. It’s the hottest planet in our solar system, even though Mercury is closer to the Sun.

Another big difference from Earth – Venus rotates on its axis backward, compared to most of the other planets in the solar system. This means that, on Venus, the Sun rises in the west and sets in the east, opposite to what we experience on Earth.

Venus was the first planet to be explored by a spacecraft – NASA’s Mariner 2 successfully flew by and scanned the cloud-covered world on December 14, 1962.

As it sped away in February 1974, NASA’s Mariner 10 spacecraft captured this view of Venus showing a world wrapped in a dense layer of toxic clouds. The clouds whip around the planet at about 100 metres per second circling the globe in about four and a half days. Credit: NASA/JPL Caltech

Mercury

Mercury returns to have western evening twilight this month and is best seen late in the month sharing the sky with Venus, Saturn and Jupiter. On the 27th the duo of Mercury and Venus will be parallel to the horizon and best viewed about 30 minutes after sunset. They appear at their closest on the 29th .

Venus is still shining brilliantly in the western evening sky, and you certainly can’t miss it.  After eight months as the Evening Star, Venus is now rapidly heading back toward the Sun. and by the end of the moth it will be lost in the Sun’s glare as it nears inferior conjunction early in January.

Venus reaches its brightest on the 4th at -4.7 magnitude – known as greatest illuminated extent. It is defined as when the planet’s illuminated portion or day side covers the greatest amount of sky. At this time, we see Venus one-quarter illuminated, just like a 3- or 4-day old Moon. On the 7th the 4-day old waxing crescent Moon appear about 5° above the planet.

The planets after sunset on 29th December 2021 in the Western Sky

Earth

The Earth is at Solstice on the 22nd when the days are longest. On this day, the Sun is at its most southerly position with a declination of -23.5°.

Mars

Mars is now visible in the eastern dawn sky in the constellation of Libra during the first half of the month. It will then cross into the claw region of Scorpius and lastly into Ophiuchus. On the 3rd, the planet will be 4° to the south of the slender crescent of the waning 28-day old Moon – binoculars and a good eastern horizon will help you see it in the dawn sky.

The Moon and Mars in the early morning sky on 3rd December 2021.

Jupiter

Jupiter stands out in the western sky at the end of twilight, the only bright star nearby being 1st magnitude Fomalhaut in Piscis Austrinus. If you want to view the planet through a telescope, you should do so early in the month before it loses too much altitude. Jupiter’s brightest has decreased a little over half a magnitude since it’s opposition last August. Its equatorial diameter has also diminished by 32%. On the 9th, the 6-day old waxing crescent Moon will be 4° from the planet.

Saturn

Saturn is visible low in the western evening sky, setting around 10 pm mid-month. Although a little too low for meaningful telescopic observations of the planet, waxing crescent Moon provides a pleasant visual display at the end of twilight. First, on the 7th the Moon will be seen near Venus, then on the following evening near Saturn and finally on the 9th near Jupiter. With each visit the Moon appears within 5° of the planet.

Uranus

Uranus now past opposition, is in the northern evening sky at the end of astronomical twilight in Aries, transiting the meridian around 9 pm mid-month.

Neptune

Neptune comes to the end of five months in retrograde on the 2nd and appears high in the early north-western evening sky at the end of astronomical dusk.

METEOR SHOWERS

A casual observer may watch the sky at night and see 3 to 5 sporadic meteors per hour. However, on some nights, this number may increase markedly, and on projecting the paths of the meteors back, we find that many appear to radiate from a tiny area in the sky. This point or place is termed the radiant of the meteor shower.

Geminid Meteor Shower

The Geminids visible from December 4th to December 20th are considered to be one of the most spectacular meteor shows of the year, with the possibility of seeing around 120 meteors per hour at its peak, which is on December 13 or 14, depending on your time zone.  The waxing gibbous Moon will be a hindrance until after 2 am but from then until dawn the sky will be Moon free.

This is the one major shower that provides good activity prior to midnight as the constellation of Gemini is well placed from midnight onward. The Geminids are often bright and intensely coloured. Due to their medium-slow velocity, persistent trains are not usually seen. These meteors are also seen in the southern hemisphere, but only during the middle of the night and at a reduced rate.

The shower owes its name to the constellation Gemini because the meteors seem to emerge from this constellation in the sky. Whereas most meteor showers are associated with comets this one is associated with an asteroid 3200 Phaethon.

Looking for Christmas Gift Ideas?

Why not grab the 2022 Astronomy calendar, which also includes the amazing photos and information on the planets, moon phases and sky maps for each month –$19.95

Want to get the best information for what is in the sky each month? Grab your copy of Astronomy 2022 Australia available from our website. Only $29.90 for a year full of fantastic information on what you can see in the sky – even without a telescope.

Clear skies until next month! Stay up to date on my Facebook page.

Donna the Astronomer

I am a keen astronomer lucky enough to live and work in Coonabarabran the Astronomy Capital of Australia! I am a ‘Drover’s Brat’ and discoverer of a couple of comets and asteroids. I operate Milroy Observatory and can show you how to best integrate dark sky experiences into your tourism, farm stay or AirBnB business.

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