The night sky for December 2018

Northern Hemisphere

Ian Morison tells us what we can see in the Northern Hemisphere night sky during December 2018.

The Planets

• Jupiter - Jupiter passed behind the Sun on November 26th and will appear low in the eastern pre-dawn sky around the 12th of the month. It will have a magnitude of ~-1.8 and a disk ~32 arc seconds across. It is not a good month to observe Jupiter due to its low elevation, but do see the 'highlight' above.
  
  
• Saturn - Saturn might just be glimpsed in the first few days of December very low in the southwest around 16:45 but soon disappears into the Sun's glare as it moves towards superior conjunction on January 2nd. It will have a disk of ~15 arc seconds and a magnitude of +0.5.
  
  
• Mercury - Mercury passed between us and the Sun (inferior conjunction) on the 27th of November but appears in the pre-dawn sky around the 6th of the month. It will then have a magnitude of +0.5 which increases to magnitude 0 by the 8th. Mercury reaches its greatest elongation (west) of the Sun on the 16th, when 21 degrees away and rising over an hour and a half before it when it is ~60% lit. As the morning ecliptic is at a steep angle to the horizon at this time of the year, this is an excellent apparition. Do not miss (when hopefully clear) its conjunction with Jupiter as described above.
  
  
• Mars - Mars, though fading from magnitude -0.0 to +0.4 during the month remains prominent in the southern sky as it starts the month at an elevation of 27 degrees in Aquarius. It will lie due south around 6 pm. As the month progresses, it moves eastwards into Pisces on the 21st; slightly higher in elevation at ~32 degrees when due south around 5:30 pm. Its angular size falls from 9.3 arc seconds to 7.5 arc seconds during the month so it will become harder to spot any details, such as Syrtis Major, on its salmon-pink surface.
  
  
• Venus - Venus begins December at an elevation of ~32 degrees and with a dazzling magnitude of -4.9. Its angular size reduces from 40.7 to 26.6 arc seconds during the month as it moves away from the Earth but, at the same time, the percentage illuminated disk (its phase) increases from 26% to 47% - which is why the brightness only reduces from -4.9 to -4.6 magnitudes. It will reach greatest elongation from the Sun on January 6th.
  
  

Highlights

• Comet46P/Wirtanen rises high in the sky and may be visible to the unaided eye. This month we have a chance of seeing a comet with our unaided eyes as it could reach magnitude +3. The chart shows its position during the month as it rises above the southern horizon through Taurus and Auriga. On the night of the 16/17th December it will pass between the Pleaides and Hyades clusters in Taurus - making a wonderful imaging opportunity if clear. Then, on the night of the 24th, it will lie very close to Capella in Auriga (but sadly, the Moon will then be full).
  
  
At closest approach on the night of December 16th it will be only 30 times further than the Moon. Then its coma should be about 1 km in size and span one degree across. The waxing gibbous Moon will hinder our view early on that night but will set at 1 am, so it is worth staying up late if it is clear!


• December 3rd - before dawn: Venus below a very thin crescent Moon. Looking southeast before dawn one should, if clear, be able to easily spot brilliant Venus lying below a very thin crescent Moon. Spica is over to the right of Venus making a nice photo opportunity.
  
  
• December 7th - 1 hour after sunset: A very close conjunction of Mars and Neptune. Looking south after sunset one should, if clear, be easily able to spot Mars. But when it gets fully dark, with binoculars or a small telescope, Neptune should appear just down to its lower right. A great opportunity to find Neptune - let's hope it is clear!
  
  
• December 14th - after sunset: Mars will lie 4 degrees above the First Quarter Moon. Looking south after sunset one should, if clear, be able to spot Mars lying about 4 degrees above the First Quarter Moon making a nice photo opportunity.
  
  
• 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. The Moon is at First Quarter and will set around 11 pm so, when Gemini is highest in the sky, its light will not hinder our view. The Geminids can often produce near-fireballs and so the shower is well worth observing if it is clear. 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 21st - just before dawn: Jupiter and Mercury together with Venus above. If clear just before dawn, and given a low horizon towards the east, one should be able to see Mercury lying a little above Jupiter making it appearance in a new apparition. Venus will be shining brightly up to their right. A nice photo opportunity.
  
  
• 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. Sadly, this year Full Moon is on the 21st, so its light will greatly hinder our view. 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 it is worth having a look should it be clear.
  
  
• December 16th (late night) and 17th: Two Great Lunar Craters. This is a great night to observe two of the greatest craters on the Moon, Tycho and Copernicus, as the terminator is nearby. Tycho is towards the bottom of Moon in a densely cratered area called the Southern Lunar Highlands. It is a relatively young crater which is about 108 million years old. It is interesting in that it is thought to have been formed by the impact of one of the remnents of an asteroid that gave rise to the asteroid Baptistina. Another asteroid originating from the same breakup may well have caused the Chicxulub crater 65 million years ago. It has a diameter of 85 km and is nearly 5 km deep. At full Moon - seen in the image below - the rays of material that were ejected when it was formed can be see arcing across the surface. Copernicus is about 800 million years old and lies in the eastern Oceanus Procellarum beyond the end of the Apennine Mountains. It is 93 km wide and nearly 4 km deep and is a clasic "terraced" crater. Both can be seen with binoculars.
  
  

Haritina Mogosanu from the Carter Science Centre in New Zealand speaks about the Southern Hemisphere night sky during December 2018.

Introduction - Kia Ora from New Zealand, here at Space Place at Carter Observatory in the heart of Wellington in the Southern Hemisphere, Haritina Mogosanu and Samuel Leske are your hosts for December 2018.

Space Place - Space Place is one of the historical icons of New Zealand in terms of astronomy, located at the heart of our capital city. There's not many capital cities where the Milky Way is visible on a dark night so we're very lucky in Wellington to have a city not totally given over to light pollution.

We have amazing historical telescopes, a 23 cm Cooke built in 1867 that we use for public viewing and we also have a retro Boller and Chivens 16". The Cooke has quite a story behind it and how it got to New Zealand and eventually how it ended up in Wellington. It has been a very important telescope for research including being used to photograph Halley's Comet in 1910.
Also on display is a James Short telescope. We only look at this one - and not through, it's locked in the displays. It's a very important telescope that we believe came here with Captain Cook and it was donated by Adam Read; he is the son of Peter Read, the creator and presenter of the New Zealand's Night Sky TV show in the 1960s.
We also have a beautiful planetarium where I spend a lot of my time.
If you ever wish to find us, Space Place is at the top of the botanical gardens looking out to the harbour, and surrounded by flowers and New Zealand birds that are amazing so you can imagine the views, and the sound, both day and night. We actually have a bunch of New Zealand owls in a tree right in the front of us, they are called morepork and we can always hear them when we look through the telescopes.

Observing in December - We have some instructions for you as to what to do with the December night sky. For those of us who don't read the instructions, we just have some amazing stuff that we wish to share and those who do neither instructions nor stories, here's the gossip.

Did you know there's going to be a comet in the December night sky? How about a Meteor Shower? And a Full Moon? And the Summer Solstice?
And did you know that this Christmas we celebrate 50 years since we went around the Moon? Also in December, the Americans are aiming to land a probe on an asteroid to get a sample and, - my favourite - someone calculated all the starlight that adds up in the Universe, so starting this month we will be fully informed about how many photons are reaching Earth, since the dawn of time, or so they say.

Here is what you need to do. Look for the comet around the 16th of December. It should appear on the Eastern horizon just in between the Pleiades and the Hyades. Perhaps take a picture of it too, just because you can, it's going to be really bright. Keep an eye on our site for instructions for how to do that if you need help.

Look for the meteor shower anytime between 7 and 17 of December (that is, yes you're right almost in the same time as the comet.) It's the Geminids so the radiant (the point in the sky that seems to "rain stars") is in the constellation Gemini.

Moon - With the full Moon, - now depends if you are into moonlight or not. I'm not, it casts too much light and I cannot see the stars properly, so I'm trying to avoid it as much as I can. The good news is that the first two weeks are good for observing, since the New Moon will be on the 7th of December. The awesome thing is that this month's full Moon will coincide with the Apollo 8's 50 years around the Moon celebration.

Shortest Night - Just a few days before that, at 11:23 AM on Saturday 22 December, Earth will be at its maximum tilt towards the Sun. What does it mean for us? Well, it will be the shortest night and with the Moon almost full, best thing we can do is just celebrate light. Speaking of which, our Sun went stealth, it's in a minimum of a minimum but just because we can't see any spots it doesn't mean there's nothing to learn about it. The Parker solar probe has now joined the rest of the successful missions out there and we are looking forward to some good data from it.

Comet Party - Since December is the month of major celebrations, we think a star party might be in order. If you have never been to one, here's a great opportunity. It could be a Moon party if it's around Christmas or else a star party could work around the 7th of December more or less a few days.

Now the trick is the night is extremely short - we wanted to photograph 47 Tucanae the other day and had to wait until 9:22 pm and even then there wasn't good enough for proper imaging, only for lining up. So your efforts might be best conserved to try and find the comet, here's a comet party, we don't get these too often and I do remember a few years ago a comet appeared in the New Zealand Sky around this time. It was fun and it wasn't as bright as this one, we needed telescopes then to see it. This one is a naked eye comet.
So a comet-party seems like a good idea. The best time to look at it is just after sunset and on the 16th of December will have the magnitude of approximately 3. What does that mean? It means we can see it with the naked eye.
Have you ever tried to pronounce a comet's name? 46/P Wirtanen (go pronounce that in one word!) P stands for periodic and 46 is that it's the 46th to be discovered (in case you were wondering, the first ever was Halley's comet). Wirtanen will arrive from the direction of Cetus / Eridani and is very tiny. Only 1.2 km in diameter, Wirtanen has a short period too, 5.4 years.
What's cool is that this comet was the original target for ESA's Rosetta spacecraft but the launch window was missed so they sent the probe to another comet with an even better name (just because is longer and harder to pronounce) 67P/Churyumov-Gerasimenko.
What's a magnitude 3? If you ever managed to spot the famous galaxy Andromeda, then you have the answer. Something that looks like Andromeda (3.4).
Now that you know where to look, and what you might find, the comet can be your centrepiece for the comet-party. But nothing says that you should not look at the stars and deep sky objects.

Star Party (and Deep Sky Objects) - New Zealand is in a great spot for observing the night sky, and we, of course, get the whole Southern Sky but also a reasonable chunk of the Northern Sky as well. We can't see the stalwarts of the Northern Sky such as the Big Dipper and there's no taking in the beautiful face on spirals of M51, the Whirlpool Galaxy, or M101 the Pinwheel Galaxy.

At this time of the year the nights are getting shorter and shorter and the telescopes of the early evening are being swapped with BBQs and the smell of lithium grease is replaced with the smell of burnt sausages. But while some of our fellow Wellingtonians are going to bed or spinning embellished stories around the embers of their BBQ we are cracking open the Space Place Domes and collecting some ancient photons.
Some favorites of mine are visible in the night sky and the early part of the month will be ideal to try and see them given the Moon will be well hidden. The first of these is M74 and unfortunately, despite all of the aperture we have available at Space Place, we are not going to see this one visually because of it's very low surface brightness. We'll have to borrow the van and take the portable Meade over the hill to the very dark skies of the Wairarapa to see this beautiful face on spiral. Luckily it's not all bad for galaxy hunting in December as not too far from M74 is the bright galaxy of M77 - also known as Cetus A. This one is easy to spot even from central Wellington. We won't see the faint outer regions of the spiral arms but the bright active core is very visible and at 33 Million light years distant the photons from this object have spent a long time making their way to Wellington.
Despite not having M51 and M101 to look at, we do have some very impressive galaxies in the Southern Sky. One of these is NGC 253 - also known as the Sculptor Galaxy. This is large spiral galaxy at an angle to us so it looks like an elongated ellipse. It's relatively bright and easy to spot it you've got plenty of aperture. You'll have to put your light bucket on the back of your scooter and head to a dark sky location to make out much detail, but if you do, you'll be in for a treat as you take in the complex shapes and clumps of detail visible on the disk. Sculptor is about 12 million light years away appears about 27 arcminutes long so is quite big.
Quite close to Sculptor is the tight spiral galaxy known as NGC 300. This is a great galaxy to view as it's quite close at only 6.6 million light years - for Northern Sky observers it's a bit like a mini M33. Viewing from Wellington will show the bright core but you'll have to head to the hills to get any detail out of the spiral arms. Keen astrophotographers will have a better time in Wellington as this galaxy is bright enough to burn through the light pollution and produce quite a nice picture.
The problem with viewing galaxies is that they don't really look anything like the beautiful photographs people take. They are often just a faint gray smudge in the eyepiece and you have to use your best visual observing skills to get any detail out of what you're looking at. This is when it's great to swing the telescope around to the majestic brilliance of the likes of the Tarantula Nebula. This gives you a picture in the eyepiece very similar to what photographers capture, just not in colour. This big giant bright complex of gas clouds and massive stars looks a bit like a spider, hence its name and it is a must see of the Southern Sky and is almost compulsory viewing on any observing evening.

Moon Party - If all the above fails, you could always have a Moon Party.

That could be really spectacular since exactly 50 years ago the first people orbited around the Moon, the astronauts of Apollo 8. Some amazing things happened during that flight including taking the picture that changed the world, Earth rise. One little picture is credited as the most important legacy of the Apollo programme, showing Earth half hanging in shadow and suspended in the middle of nothing at all. Humans saw their planet for the first time as a whole world, a small, blue, finite globe in the distance. It's the image that is credited with starting the environmental movement and has been used as a hopeful symbol of global unity. So we think if you're going to have a Moon Party this December it's going to be pretty cool. Again, keep an eye on our website, as we will post some more content there.

Mars - There's one more thing I want to talk about, Mars.

Mars will always have a special place in my heart and now has a new resident, InSight. InSight was the mission that brought the first cubesats to Mars and now sits happily on the red planet stretching its arms. Literally.
We wish you happy hunting for comets and galaxies this month, and if all that doesn't work then grab yourself a couple of craters on the Moon.

Clear skies from Haritina and Sam here at Space Place at Carter Observatory in Wellington New Zealand, and see you next year!