December 2020

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 17^th, but the day of closest approach is the evening of the 21^st 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, 21^st 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 23^rd and 24^th 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 13^th 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.

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 6^th 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