February 2019

Planets to look for

A fading, unimpressive Mars is the only planet of note in the evening sky during February. Mercury is on the evening side of the Sun, but too close to be seen; wait until it returns to the morning sky in late March and April to see it. But back to Mars, particularly if you have a small telescope or even binoculars, as the aqua-green planet Uranus will glide past within one degree of it on the 12^th and 13^th of February. To give you an idea of this separation, a full moon is about 0.6 of a degree in width, so Mars and Uranus will be almost two full moon-widths apart.

Jupiter starts the month rising at 1.30am but by the start of March it will be rising before midnight. However it will be late April before it becomes an easy evening target.

Saturn and Venus put on the early morning show this month. Venus starts it with a spectacular pairing with the waning crescent moon on the 1^st of February, then it takes nearly three weeks for Saturn to catch up with Venus up above it on the 19^th. By the end of the month Saturn is rising at 2am.

Constellation of the month

Puppis the Stern

In ancient times there was a huge constellation known as Argo Navis, which represented the Greek ship Argo, made famous from the Greek myth of Jason and the Argonauts who went to fetch the Golden Fleece. To make things a little easier a French astronomer called Nicolas-Louis de Lacaille split the ancient constellation into four smaller ones: Carina the Keel, Vela the Sails, Puppis the Stern and Pyxis the Compass. (Actually, there was an attempt to make one part Malus the Mast but it wasn’t very popular and soon forgotten.) Puppis, the westernmost section of Argo Navis, is well placed for exploring this month.

Puppis takes up a large area to the south of Canis Major, with part of it stretching underneath the Big Dog’s back. Or you can start from Canopus, the second brightest star in the sky, and follow the pattern of the Stern from there.

The star clouds of the Milky Way run through the middle of Puppis and an observer scanning this area with binoculars will many clusters of stars.

Puppis is to the south of Canis Major, the Great Dog.

One problem we have looking at the sky is that distance is hard to perceive. We can be looking in one direction and seeing several objects that lie at different distances, even though it appears they are all together in the sky. When we look up and out at a lovely open cluster of stars known as Messier 46 (also NGC 2437) in Puppis the Stern, we encounter this problem as well.

M46 is a roundish group of 500 stars that are about 300 million years old, so could be considered middle-aged for an open cluster of stars, stars that all formed together out of the same cloud of gas and dust. They’ve done well to survive one full rotation around our galaxy, which is considered to take about 250 million years.

They seem unremarkable until you look a little more carefully on the north side of the cluster, where a small, round nebula appears over the top of cluster. This little planetary nebula is a ring of gas thrown off by a dying star that was probably not much bigger than our Sun. Ultraviolet light from that dying star is making the gases glow at the moment, for a brief 10,000 years or so. But when we measure the distance to this planetary nebula astronomers find it is well in front of the open cluster, only 3000 light years away compared to 5,400 light years for the cluster. So we just happened to be in the right place to catch them passing each other by.

If you have trouble seeing the little planetary nebula use your averted vision – look away from the nebula and it should appear to jump into view in the corner of your eye. If you look back directly at it, it will disappear again. Look away, look back; you should be able to make it blink on and off. The edges of your eye are more sensitive to shades of brightness, while the centre of your does the colour detecting in bright daylight, which is why it seems to only appear when your vision is averted.

M46 can be found under Canis Major (to the east.)

The Goddess of the Moon and the Jade Rabbit

The beginning of January was a busy time for followers of space exploration both near and far. On the 3^rd of January the Chinese lander Chang’e 4 made a successful landing on the far side of the Moon and the small rover Yutu 2 rolled off it onto the Moon’s surface.

Chang’e 4 on the surface of the Moon, taken by the Yutu 2 rover (tracks are visible on the right-hand side of the image).

By CNSA

Chang’e 4 is named after the Goddess of the Moon, and Yutu is the Jade Rabbit who is a companion to Chang’e. There was a Chang’e 3 and Yutu 1 in 2013 that was a successful mission and this is a follow-up mission, to the far side of the Moon. Because we see we only see one side of the Moon, as it is gravitationally locked towards us, a communications relay satellite was sent up in May 2018 to circle inside what is known as the L2 point, or Langrangian 2 point, on the far side of the Moon as well, where the gravitational pull of the Moon and Earth cancels out. This satellite is called Queqiao, or “Magpie Bridge.”

You might be wondering why the Chinese have gone to all this trouble of putting a lander on the far side of the Moon, if it means so much work. But there is a very good reason to do so – they have landed Chang’e 4 inside one of the craters in the solar system, called the Aitken Basin. It is 2,500 km across and 13 km deep, and they have landed Chang’e 4 in this 13 km deep area in the hope that they may find parts of the Moon internal crust exposed at the surface.

Chang’e 4 also tried to run an experiment growing plants and hatching insects, but the chamber was not kept warm enough and the plants that germinated soon died.

Future Chang’e missions are planned, ones that will collect samples of Moon rock and soil and send them back to Earth. In the mean time we will all look forward to what Yutu 2 might find in its travels.

The lunar rover Yutu 2 rolls out onto the Moon’s surface.

Credit: Chinese Lunar Exploration Program (CLEP)