The Sky Tonight is a monthly update of the amazing things you can find when looking up from here in Western Australia. This section is written by Jacquie Milner, resident astronomer at the Scitech Planetarium.
The casual observer
The summer solstice for the southern hemisphere occurs on December 22nd 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, but the waning last quarter Moon could drown out the fainter meteors this year.
An update on the interstellar visitor A/2017 U1 mentioned in last month’s feature section: It has been given a name and had a new designation created for it! It is now known as 1I/ ‘Oumuamua, where the “I” stands for “Interstellar” and ‘Oumuaua is a Hawaiian name meaning “the first to reach out” or “advance scout.” You can read the official release describing the reasoning behind the name and new designation from the Minor Planet Centre here.
Dates of interest
14th – Crescent Moon to the lower left of Mars, morning sky
15th – Thin crescent Moon to lower left of Jupiter, morning sky
22nd – Solstice
31st – Bright Jupiter and red Mars either side of the star Zubenelgenubi (alpha Librae), morning sky
Planets to look for
After the first week of December, the evening sky will be empty of planets for a while. Mercury and Saturn star the month together, low in the evening twilight to the south of west, but they quickly sink into the evening twilight.
Once that happens, you will just have to enjoy the Moon and stars for a while.
Mars is now rising around 2.30am, but still won’t be much to look at through a telescope. Jupiter rises less than hour later, and over the course of the month seems to speed up a little so that by New Year’s Eve the two planets are rising almost together. On December 31st they will frame the star Zubenelgenubi (“The southern claw”) as they rise – Jupiter will be the brightest of the pair.
Venus is now lost in the Sun’s glare and will be out of sight for several months. We will next see it in the evening sky in March 2018.
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.
Objects 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.
Sir Arthur C. Clarke 100th Anniversary
This December is the 100th anniversary of the birth of Sir Arthur C. Clarke, on 16th December 1917. Even if you haven’t heard of him your life is no doubt touched by him in some way. He didn’t work as an astronomer or in the space industry but he had a huge influence on the many people that did.
In 1945 he proposed a system of “rocket stations” that might give world-wide radio coverage. Although he wasn’t the first to come up with this idea, he gave the clearest description of the concept of we now call geostationary satellites to date. This orbit, which is about 35,786 km from the Earth, is called the Clarke Belt in his honour. Next time you watch a live sports game from overseas, you will probably be benefiting from a satellite sitting in this zone.
He was also famous for his science fiction novels, particularly “2001: A Space Odyssey” which he wrote as part of the process of developing the screenplay for the movie of the same name, with director Stanley Kubrick. Still widely regarded as one of the movies of all time, its subjects of a troublesome self-aware computer and also life on other bodies in the solar system are still hot topics today. He wrote 25 novels in all.
He moved from the UK to Sri Lanka in 1956, where he lived the rest of his life. He was a keen scuba diver. He passed away on 19 March 2008, aged 90.