Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during December 2016.

• Venus below a thin crescent Moon

  After sunset on December 3rd, looking low towards the south-southwest, Venus shining at magnitude -4.2, will be seen, if clear, below a very thin crescent Moon.

• December 4th after sunset: Venus, Mars and a crescent Moon

  If clear after sunset on the 4th, looking low towards the south-southwest it should be possible to see a thin crescent Moon to the upper left of Mars with Venus well down to its right.

• December 13 before dawn: The Moon Occults Aldebaran in the Hyades Cluster

  During the night of the 12th/13th December, the Full Moon will pass throught the Hyades Cluster and occult many of its stars. At around 6:15 UT on the 13th, it will occult -0.7 magnitude Aldabaran which lies between us and the cluster. This may be a grazing occultation from parts of the UK.

• December 14th and 15th after midnight: the Geminid Meteor Shower

  The early mornings of December 14th and 15th will give us the chance, if clear, of observing the peak of the Geminid meteor shower. Sadly, this is not a good a year as these nights are just after the Full Moon and the fainter meteors will not be seen. However, as I saw last year, the Geminids can often produce near-fireballs and so the shower is still well worth observing. An observing location well away from towns or cities will pay dividends. The relatively slow moving meteors arise from debris released from the asteroid 3200 Phaethon. This is unusual, as most meteor showers come from comets. The radiant - where the meteors appear to come from - is close to the bright star Castor in the constellation Gemini as shown on the chart. If it is clear it will be cold - so wrap up well, wear a woolly hat and have some hot drinks with you.

• December 22nd/23rd - late evenings: the Ursid Meteor Shower

  The late evenings of the 22nd and 23rd of December are when the Ursid meteor shower will be at its best - though the peak rate of ~10-15 meteors per hour is not that great. Pleasingly, the Moon will not affect our view during much of the night. The radiant lies close to the star Kochab in Ursa Minor (hence their name), so look northwards at a high elevation. Occasionally, there can be a far higher rate so its worth having a look should it be clear.

• December 30th/ 31st after sunset: Venus closes on Mars

  After sunset at the end of the month, Mars, in Aquarius will be seen to the upper right of Venus low in the south-southwest.

• December 6th and 20th: The Alpine Valley

  These are good nights to observe an interesting feature on the Moon if you have a small telescope. Close to the limb is the Appenine mountain chain that marks the edge of Mare Imbrium.Towards the upper end you should see the cleft across them called the Alpine valley. It is about 7 miles wide and 79 miles long. As shown in the image a thin rill runs along its length which is quite a challenge to observe.Over the next two nights following the 6th the dark crater Plato and the young crater Copernicus will come into view. This is a very interesting region of the Moon!

Haritina Mogosanu from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during December 2016.

• We'll start our tour in Orion, sitting high in the east after dark. Orion lies along the celestial equator, and can be seen (at least partially) throughout the world. As he was invented in the Northern hemisphere, in New Zealand we see him upside down. Orion contains a number of interesting objects to observe with both binoculars or telescopes. If you look carefully you may see the middle star of Orion's sword has a fuzzy appearance. This is the Orion Nebula, which is a stellar nursery, a huge cloud of gas and dust in which new stars are being born. In the heart of the Orion nebula is a small group of bright stars known as the Trapezium Cluster. The ultraviolet radiation from these stars is lighting up the surrounding gas.
• Following Orion's belt to the left we come to an upturned V shape of stars marking the head of Taurus the bull. At the bottom of this V is the bright orange star Aldebaran, at around 65ly away, representing the eye of the bull. The other stars in the V are part of the more distant Hyades cluster. At 153 ly away, the Hyades is the closest, and one of the best studied, open clusters to Earth. It is estimated to be around 625 million years old. Over time the cluster will continue to spread out and disperse into space, with some of the largest and brightest members already coming towards the ends of their lives.
• Following Orion's belt to the right, you can follow the band of the Milky Way around the sky, through the False and Diamond Crosses to Crux, the Southern Cross, low in the south. Sat beside the Southern Cross is a dark patch called the Coal Sack Nebula. Known as a dark nebula, the gas and dust in this cloud is blocking the light from more distant stars, obscuring them from our view. To Maori the Coal Sack Nebula is known as Te Patiki, or the Flounder.
• In our western skies, we see a trio of planets this month. Mercury is low on the southwestern horizon for the first half of the month, setting around an hour and a half after the sun, before sinking into the evening twilight after the 15th. Venus is higher in the west, the first thing you'll see as the sky begins to darken, and sets close to midnight. Mars is much fainter and to the top right of Venus, moving through Capricorn and into Aquarius over the course of the month
• The Phoenicids reach their peak on 6th December and are thought to be associated with the comet D/1819 W1 (Blanpain). With the radiant in the constellation of Phoenix, not far from Achernar, this shower is well placed for southern hemisphere observers throughout the hours of darkness. The minor Puppid-Velids meteor shower also reaches its peak at around the same time with a zenithal hourly rate of around 10.
• The Geminids are peaking on the 15th of the month. This is one of the best meteor showers of the year, but we are not well placed for viewing in New Zealand, with the radiant in the constellation of Gemini and well north of the equator. The constellation is at its highest around 3 am, but still appears low in our northern sky. Due to this low height we only see around half of the meteors visible to those in the northern hemisphere.