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The Sky Tonight

The Sky Tonight is a monthly update of the amazing things you can find when looking up from here in Western Australia.

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The casual observer

The summer solstice for the southern hemisphere occurs on December 21st this year. The sun is the furthest south in the sky for the year and after this the days begins to get shorter for us again. Sunsets will keep getting later, however, until early January when the Earth reaches perihelion, the closest it gets to the sun in its orbit.

Mid-December is also time for one of the best meteor showers of the year for the southern hemisphere, the Geminids. The peak time for the shower are the nights of the 13th and 14th of the month, so you may notice more meteors than usual around this time. This year they occur just before New Moon, which means no Moon to wash out the fainter meteors, but it’s on a Sunday and Monday night. Best viewing for meteors is after midnight, but you may see some earlier in the night as the radiant is above the horizon most of the night.

Be prepared for a Great Junction social media onslaught this month! Jupiter and Saturn meet up for their once every twenty years conjunction low in the evening sky this December, but what is special about this one is that it will be the closest one witnessed since Medieval times in 1226 AD. Coincidentally closest approach occurs on the evening of the solstice, December 21st  although they will appear . If you miss this conjunction you will have to wait until 15th March 2080 to see another this close – The conjunctions in 2040 and 2060 will be much wider apart.

At their closest approach Jupiter and Saturn will appear as two distinct bright stars low in the west at the end of evening twilight on the 21st December.

Phases of the Moon

Last Quarter

December 8

New Moon

December 15

First Quarter

December 22

Full Moon

December 30

Last Quarter

December 8

Dates of interest

  1. Waning crescent Moon next to Venus, morning twilight

    December 13

  2. Crescent Moon next to Jupiter and Saturn, early evening

    December 17

  3. Solstice

    December 21

  4. Jupiter and Saturn only 0.1 degree apart, early evening

    December 21

  5. Moon above Mars, evening sky

    December 24

Planets to look for

Jupiter and Saturn hog the spotlight this month, with their once-in-twenty-years conjunction, and a spectacularly close one at that as well. The Moon will join them on the evening of the 17th, but the day of closest approach is the evening of the 21st of December, the same day as the Solstice. For a week surrounding this day they will both fit in the same field of view of a telescope eyepiece but at closest approach they will be only 0.1 degree apart. A simulated view of what observers will see is depicted below (it may appear upside down, or reversed, depending on the arrangement of your optics.) In comparison, the width of an average Full Moon is 0.6 degrees.

The position of the brightest of Jupiter’s and Saturn’s moons on the night of their conjunction, 21st December, 2020.

Mars looks quite lonely in comparison, still in Pisces after several months. It is now in the north west as it gets dark. The Moon passes by on the 23rd and 24th of December.

Venus continues to cruise along the top of the morning twilight line to the south, moving from Virgo to Libra. A slender waning crescent Moon will join it on the morning of the 13th at a separation of only one degree, which will make a pretty sight for early risers.

Mercury spends this December too close to the Sun to be seen. Keen observers may be able to observe it in the evening twilight during late January.

Constellation of the month

Aries the Ram

Aries is famous for being the first constellation of the Zodiac. Around 2000 years ago the vernal equinox (in March) occurred there. This equinox, when the sun passes from the southern hemisphere to the northern, was important to the ancient people of earth as it marked the start of spring and the New Year. Today, due to the precession of the poles, the vernal equinox occurs among the stars of Pisces, but Aries still retains his leading status.

Aries is not a very eye-catching constellation. It is primarily marked by three bright stars in a curve and you could extend it further to a fourth is you wish. These stars can be seen as marking the curve of the Ram’s back.

There are various stories as to how a sheep ended up in the sky. One story is that is the Golden Fleece that Jason and the Argonauts sought. Another that it is the sheep that Odysseus hid under as he escaped from the Cyclops during his long journey back from Troy.

The brightest star is called Hamal, which is Arabic for ‘lamb’.

Look northwards to find Aries the Ram in our summer skies from Australia.

Object for the small telescope

The Pleiades (The Seven Sisters)

The Pleiades is also known as the Seven Sisters.  It is a cluster of young stars that lies about 420 light years away. A quick count of the brighter stars in this cluster usually reveals only six (although sharp eyes will almost certainly see a few more). It is an international mystery as to why we call them the Seven Sisters when we see only six stars. There are many stories in myths and legends from many different cultures as to why it might be so but no one really knows why. How many stars can you see in the cluster? Binoculars are a good way of enjoying this object.

The Pleiades are part of the constellation of Taurus. The Hyades make the face of the Bull and Aldebaran, “The Follower” (it is following the Pleiades), marks one of the Bull’s eyes.

Hayabusa2 Returns its Sample to Earth

The fiery return of the sample capsule from the first Hayabusa mission, seen in 2010. Credit: NASA

 

On 6th December all eyes will be skyward at the Woomera Test Range in South Australia as they await the fiery re-entry of the sample capsule from Hayabusa2.

This Japanese mission to a small asteroid they named Ryugu, or “Dragon’s Palace” after a Japanese folk tale has been active since launch in 2014 and now the primary phase of the mission is nearing its end. How much sample did it collect? What will the sample look like? Everyone is bursting with excitement to find out. But first the sample capsule has to reach the surface of Earth and be recovered, while Hayabusa2 sails on towards an extended mission.

 

The mission patch for the sample return to Earth.

 

The Japanese Space Agency, known as JAXA, first tried to sample an asteroid with Hayabusa, which means “Peregrine falcon.” They overcame many problems on this mission, with a failure in the drive which meant the mission took longer than expected, then they weren’t sure if they had collected any sample from 24143 Itokawa, the asteroid they had chosen on that first mission. Only a few grains of dust could be found in the returned sample canister. But they learnt from this, and built a second sample-return mission, Hayabusa2, and it has run much more smoothly than the first.

Asteroid Ryugu as seen from Hayabusa2 from 20km distance.

Image credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu and AIST.

 

Two samplings of Ryugu’s unexpectedly rocky surface were collected, but a third planned sampling touch-down was cancelled to reduce the risk of damage to the spacecraft. It has taken just over a year to return from Ryugu back to Earth to drop of the samples in a special sample return capsule.

After Hayabusa2 drops off it’s “treasure box,” it will continue its journey on an 11 year extended mission. It will visit two more unnamed asteroids, one as a flyby and the second asteroid a 30-metre-wide object that spins once every ten minutes. How does an object that small hold itself together? You can find out more about the extended mission by watching this subtitled video and visit the Hayabusa2 mission home page to find out more about the mission and find some cute cartoon versions of the spacecraft like the one below.

Credit: JAXA

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