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 latest sunset of summer occurs on 3 January, when the Earth reaches perihelion, or the closest point in its orbit to the Sun. You probably won’t notice the evenings growing noticeably shorter until February – although the time for sunrise should have changed by about half an hour during this time.
While you’re out there enjoying the warm summer evenings, find out what satellites will be visible from your location by checking out www.heavens-above.com, also available as an app for your smartphone or tablet. Satellites will be visible nearly all night long, especially during the first weeks of January, when the Sun is still near its southern extremity and not all that far below the horizon – at least not from a satellite’s high point of view.
January sees the first of three eclipse seasons for 2019. This happens from time to time as the nodes, the place where the Moon crosses the ecliptic, line up with the Sun near the turn of the year. Neither the partial solar eclipse on 6th January nor the total lunar eclipse that occurs on 21 January will be visible from any part of Australia. But we will get to see part of the lunar eclipse in July and the solar eclipse on 26 December. More about those events as the time approaches! If you can’t wait, there are several websites to check out:
• NASA Eclipse website
Dates of interest
2 January – Crescent Moon next to Venus, morning sky.
3 January – Earth at perihelion (closest point in its orbit to the Sun), latest sunset of the year.
4 January – Slender crescent Moon under Jupiter, morning sky.
13 January – Moon above Mars, evening sky.
14 January – Saturn and Mercury together, low in morning twilight.
23 January – Venus and Jupiter together, morning sky.
Planets to look for
As the new year starts and the nights slowly begin to get longer again, the evening sky has nothing much to show in the way of planets except for Mars. However we can’t get too excited about the red planet, as it is now far away from us, travelling around the other side of the Sun from our position and continues to fall behind us. It will soon become hard to see any features on it as it is now quite small, even through a telescope. You might miss spotting Mars in the sky, as it isn’t as bright as it was six months ago when it was behind us from the Sun at opposition; The Moon will pass by it from 12 to 13 January in the evening sky.
If you are wondering that if Mars is by itself in the evening sky and this must mean the other planets are in the morning sky, that’s mostly correct. Although you are unlikely to see Mercury this month as it stays close to the Sun.
Venus is rising about 2am during January, so if you are up and about in the pre-dawn hours its bright light may well catch your eye. Jupiter climbs up to meet with it on the morning of 23 January. It’s always a pretty sight to see the brightest planets side-by-side.
Saturn also climbs out of the Sun’s glare this month, clearing the twilight a few days after Venus and Jupiter meet. Saturn has a conjunction with Mercury on 14 January, it will be difficult to see low in the bright morning twilight, so don’t feel too bad if you can’t find them. February is likely a better month for viewing the ringed planet, so if you can be patient the wait will be worth it.
Constellation of Month
The Phoenix is the mythical bird that was reborn from its own ashes. This splendid bird was placed in the sky by two Dutchmen, Keyser and Houtman, in 1798 and then adopted by Bayer for his well-known work, Uranometria in 1603. The stars of the constellation lie next to Achernar, at the end of Eridanus the River, and aren't too hard to find. There are all sorts of shapes drawn for this bird, but the easiest to find in the sky has been drawn below. The brightest star in the constellation is Ankaa, which is an anglicised form of the Arabic word for phoenix al’anqa, or “a fabulous bird.” In earlier times, Arabs saw these stars as a boat next to the river of Eridanus.
To find Phoenix, look on the opposite side of the South Celestial Pole to the Southern Cross near the bright star Achernar, which marks the end of Eridanus the River.
Objects for the small telescope
You would have likely seen the Hyades (pronounced hi-AY-dees) at some time, perhaps without realising you were looking at the nearest open cluster of stars to our solar system. The brightest stars in the Hyades make up the V-shaped face of Taurus the Bull. The bright orange star Aldebaran, “The Follower,” is not a part of this cluster, but lies in front of it.
Aldebaran, the Hyades, and the nearby Pleiades all make an interesting frame of reference in which we can compare distances in the sky. Aldebaran is closest to us, only 65 light years away. The stars that make up the Hyades are a little over twice as far than that, at 153 light years away. The Pleiades are way back in the distance at 444 light years, which is why they look so small.
We know the stars in the Hyades all belong together in the cluster as they are all moving in the same direction at the same speed. Interestingly, the open cluster in the middle of Cancer the Crab, M44 or the Praesepe Cluster, is also travelling in the same direction as the Hyades, indicating they have a common origin in the past.
Look northwards to find the Hyades during January.
New Horizons Explores the Kuiper Belt
Right at the beginning of 2019 an important milestone was reached – New Horizons flew by a Kuiper Belt object, the furthest object in our solar system to be seen up close by a spacecraft. Questions were buzzing, such as ‘what will it look like?’ and ‘what discoveries will be made?’ It’s not that often we get to see totally unknown ground for the first time, so there was a current of nervous excitement growing amongst planetary astronomers as the end of 2018 approached.
New Horizons made history when it flew past Pluto and its moons in July 2015. Instead of an icy, crater-covered world, it showed us a geologically active world with a massive heart-shaped glacier on its surface, delicate layers in its thin atmosphere of nitrogen and cryovolcanoes (volcanoes that emit ice). There were some craters puncturing the red snow, known as tholins which are complex forms of organic molecules that are created when ultraviolet light interacts with very cold gases such as nitrogen, ethane and methane – but not as many as some thought there might be.
What New Horizons saw when it flew past Pluto in July 2015.
New Horizons flew past Pluto and kept going into the Kuiper Belt, a large belt of asteroids beyond the orbit of Neptune. You may have heard of some of the large members of this belt, such as Haumea, Makemake, Quaoar, and the infamous Eris, the object that got Pluto demoted to a dwarf planet. Many of these objects also reflect back a reddish hue, indicating that they, too, are covered in tholins. But we will have to wait to find out more about them.
On 1 January New Horizons had a small body known as Ultima Thule in its camera sights, breaking the record for the most distant object ever visited by a spacecraft. Ultima Thule is only 30km across, and New Horizons flew past it at 50,700km per hour. It skimmed past it at a distance of only 3,500km giving images down to a resolution of 30m at their best. It was able to do this as astronomers went on several involved expeditions to observe Ultima Thule occult (hide) a star over the last couple of years, so they could determine its size and shape. It was revealed that Ultima Thule is what is known as a contact binary, much like what comet 67P that the Rosetta spacecraft explored and landed on and that it doesn’t have any rings or moons. Because of this they were able to fly quite close to the asteroid without trouble. You don’t want anything running into New Horizons when it’s travelling 50,700km per hour!
Image taken of Ultima Thule published Jan 2 2019, further higher resolution images are yet to come.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
An artist's illustration of NASA's New Horizons spacecraft cruising by the distant object Ultima Thule on Jan. 1, 2019.
Credit: Steve Gribben/NASA/JHUAPL/SwRI