January 2019

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. And we can’t even get excited about the red planet, as it is now far away from us, getting around the other side of the Sun from our position as it continues to fall behind us, and it will become hard to see any features on it as it is now quite small, even in a telescope. You might miss spotting it 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 the 12^th to the 13^th of January in the evening sky.

So if Mars is by itself in the evening sky, that 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 the 23^rd. 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 the 14^th, but it will be hard to see low in the bright morning twilight, so don’t feel too bad if you can’t find them. February is probably a better month for viewing the ringed planet, so if you can be patient, the wait will be worth it.

Constellation of the month

Phoenix

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, 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, so are not too hard to find. I have seen all sorts of shapes drawn for this bird but the one I like best and find easiest to find in the sky I have drawn for you 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 the Arabs saw these stars as a boat next 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.

You would have all 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 will be reached – New Horizons will fly-by a Kuiper Belt object, the furthest object in our solar system to be seen up close by a spacecraft. What will it look like? What discoveries will be made? It’s not that often we get to see totally unknown ground for the first time, so there is a current of nervous excitement growing amongst planetary astronomers as the end of 2018 approaches – although by the time you get to read this the first images from New Horizons may well have already arrived back at Earth!

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 planet 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 of tholins – 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

Image Credit: NASA/APL/SwRI

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 Houmea, 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 they, too, are covered in tholins. But we will have to wait to find out about them. On January 1^st New Horizons will have a small body known as Ultima Thule in its camera sights.

Ultima Thule is only 30km across, and New Horizons will fly past it at 50,700km per hour. It will skim past it at a distance of only 3,500km, giving images down to a resolution of 30m at their best. It will be able to 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. They think it may be 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 are confident they will be 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!

You can follow proceedings via the NASA website or on twitter at @NASANewHorizons, but it will take over six hours for the information to be sent back to us from such a far distance. Also the first news probably won’t be available until January 2^nd Australian time.

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