In the Sky in December 2017

The evening sky is mostly devoid of visible planetary landscapes, with the exception of Mars and Jupiter late in the morning and Uranus and Neptune throughout most of the night (which you will need a telescope to see).

You can read an overview of the Sky of December here.

The Planets in December 2017

As the star patterns repeat every year and so the same stars will adorn the night sky year after year in the same month of the year. But the planets,  the wanderers of the night sky, will change their positions every day, in a dance measured by what we call ‘ephemeris‘,

The planetary night scape for December is really a night of two halves. At the start of the month both Neptune in Aquarius and Uranus in Pices are visible but as Neptune is magnitude 7.9 you will need a telescope to see it at all. With a reasonable sized telescope you can make out the distinctive blue disk. Neptune is a long way away at 29.9 astronomical units (one astronomical unit is the distance from the earth to the sun), or 249 light minutes or 4,470,000,000 km.

Uranus is a little easier to see and will be visible in a reasonably powered pair of binoculars as it’s at magnitude 5.7. To make out the distinctive green disk of the planet you will also need a telescope. Uranus is about 1.5 billion kms closer at 19.2 AU or 159.6 light minutes. Given both planets are roughly the same size it shows what a difference 1.5 billion kms can make in visible magnitude.

By the end of the month Neptune sets around midnight and Uranus at about 1:30am so they are both best observed earlier in the month not long after astronomical twilight.

Uranus and Neptune
Uranus and Neptune in December 2017, Created in SkySafari Pro

Created in SkySafari Pro

If you want to catch a glimpse of Jupiter and Mars then you will only have a small window to see the before the dawn at the start of the month with Mars rising at 3:45am and Jupiter at 4:30am. By the end of the month they are both rising a little earlier at 2:45am for Jupiter and 2:30am for Mars.

As far as distances go, Jupiter is much closer than the icy gas giants mentioned above at 6.12 AU or just under 51 light minutes. So if you think about the Juno spacecraft that is visiting Jupiter right now then it takes about 51 minutes for the beautiful pictures it is capturing to return to Earth.

Image taken by NASA’s Juno spacecraft on 24 Oct 2017 from about 10,000km above Jupiter’s cloud tops during Juno’s 9th close flyby of the planet (https://www.nasa.gov/image-feature/jpl/pia21971/jovian-tempest)

The above picture is of a raging storm in Jupiter’s northern hemisphere captured by NASA’s Juno spacecraft. Back on Earth the telescope view of the planet will generally show up some of the banding and if you’ve got good conditions then you might see the Great Red Spot. The four brightest moons of Ganymede, Io, Europa and Callisto will be visible as well at various times throughout the month.

Mars is considerably closer at 1.97 AU by the end of the month which is about 16 minutes light minutes or 295 million kms. With a good sized telescope and excellent seeing conditions you might be lucky enough to see the polar ice cap, but with dawn approaching when the planet gains some altitude you need a very clear dark sky site. Without any visual aids Mars will appear it’s distinctive orange/red hue at magnitude 1.5, meaning that it will be very easy to spot just below and to the left of the much brighter, at magnitude -1.8, Jupiter. Throughout the month Mars will appear to get get closer to Jupiter, in actual fact they do get physically closer as Mars’ orbit appears to catch up with Jupiter’s. Over the course of the month they get closer by about 30 million kilometres.

Evening Sky in December 2017
Evening Sky in December 2017, Created in SkySafari Pro

Meteor showers this month

The Geminid meteor shower peaks on the morning of the 15th.  The meteors appear to come from the constellation of Gemini, low in the northeast at midnight, moving to the north by dawn. The meteors are clumps of dust from a comet, the friction from the air heats them up and makes the air around them glow.

A visiting comet to our skies

For the avid cometeer with a good telescope there’s the opportunity to see 24P Schaumasse throughout the month in the vicinity of Mars – just below and to the left, but you’ll need a good telescope as it’s visible magnitude will be around 12 and diminishing throughout the month. It will be very hard to see: very low in the horizon so you’ll need a good dark Eastern horizon.