Podcaster: Ralph & Paul
Title : Awesome Astronomy’s December Sky Guide
Organization: Awesome Astronomy
Link : www.awesomeastronomy.com
Description: What to look out, and up, for in December. We start with the broad constellation of Gemini and an easy binary star, a planetary nebula and a group of star clusters for astronomy beginners to find, before embarking on a spot of exogazing!
Next up is the return of resplendent Jupiter and Venus to our skies. We bring you the phases and conjunctions of the moon and the Geminid meteor shower in December. Then we round up the best of the deep sky offerings for the month in the winter constellations of Orion, Eridanus & Lepus.
For those in the Southern Hemisphere, 365 Days of Astronomy also play Alice Enevoldsen’s What’s Up Tonight, Southern Skies Edition each month.
Bio: Awesome Astronomy is the show for anyone and everyone who has even the slightest interest in astronomy and science.
Join Ralph & Paul twice each month, for informative and fun astronomy programs telling you what to look out (and up) for every month. You can be guaranteed a passion for astronomy, simple explanations of complex and fundamental topics, space and science news, absorbing interviews with astronomers who make the news and listeners’ astronomy questions answered
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Transcript:
Paul: December is upon us once more, the longest nights, the darkest skies and a whole host of heavenly treats to fill you with festive cheer and make it worth the effort to wrap up warm, fill up that cheeky hip flask and get outside. We have a good meteor shower, some more of those Galilean moon mutual events and a nice planetary conjunction to look forward to. So before we look at the diary what have you got on offer for the beginners Ralph?
Ralph: Well, in December we welcome back the Gemini twins. We’ve got an easy binary star, an open cluster, a faint planetary nebula and a bit of exoplanet hunting to finish with in Gemini.
Firstly, you’ll want to find the shape of the two twins Castor and Pollux which are also the names of the brightest two stars in the constellation that sit at the head of the twins. Pollux is the lower one of the two, with Castor looking slightly dimmer immediately above it. And by the end of the month they’ll be high up in the south around midnight.
Our first stop is Castor which is actually a quadruple star system but we can only easily resolve it into two stars. With a modest 60x magnification a small scope will easily split Castor into the two white stars that sit 50 light years away orbiting around their centre of gravity every 450 years or so.
Next up we go to the far end of Gemini and the outstretched leg of Castor. Actually, there’s a line of 4 open clusters all within 2 degrees of each other here, just above the highest foot. But we’re interested in the brightest cluster that appears to be sitting on top of castor’s foot. This is Messier 35 or NGC 2168 and at magnitude 5 you might just be able to see it with the naked eye in dark skies and it’s a favourite with binocular viewers. But just a little extra magnification will show the tendrils of stars that seem to emanate from a dark void in the centre. But do trace the line back down to 1 Geminorum in the foot and see how many of the 4 open clusters you can bag.
Next up is more of a challenge and I’d recommend at least a 5” scope for this. If you draw line from the star in the waist of the Castor, through to Wasat in the waist of Pollux, then extend this line for two more degrees or the width of two fingers held at arm’s length. This should find you in the right spot for the Eskimo Nebula NGC 2392. Although a faint smudge in small scopes, a larger aperture will show you the iconic face inside a Parka hood that gives this planetary nebula its name. At almost 3,000 light years away William Herschel was still able to spot this magnitude 10 fuzzy star, which we now know is shells of gas that are energised by the star in the centre.
Finally we go exogazing. We can’t spot exoplanets with amateur telescopes but we can take a look at their host stars and know the characteristics of the planets that orbit some of them. And in Gemini we have the exoplanet with the brightest host star, Pollux in the head of the lower twin in the sky.
Taking a look at this orange giant, you can know with some certainty that there is a gas giant planet called Pollux b orbiting a similar distance from Pollux as Mars is from our sun, but three times the size of Jupiter. And there are at least 6 other stars in Gemini that are known to play host to other planets.
Paul: Now turning to the solar system lets have a look what kind of show the planets are putting on for us this month.
We start with the King who is now back in evening skies after the long summer autumn absence. Those who have been up early will have already been enjoying what the largest planet has on offer but now even the evening observers can enjoy this cloud covered disc before turning in with Jupiter rising over the horizon for those at around latitude 50 before 9pm by the middle of the month. You will still need to stay up late to enjoy it at it’s best and the sight of Jupiter sitting with the constellation Leo is going to make for some great skies this apparition. There are more of those mutual events this month that we talked about last sky guide with the Galilean moons eclipsing, occulting and transiting each other through a fortuitous alignment of earth Jupiter and the sun during this season.
The 6th sees Ganymede occult Io from just after 10pm UT, the 12th sees io occulted again, this time by Europa just after 11pm UT. The 14th sees Ganymede occult Io from 9pm UT while on the 18th after 5am UT Europa will transit Ganymede- this one will be a particularly good view as jupiter culminates, that is reaches it’s highest point in te sky at about this time in December. On the 20th Europa Occults Io after 4.30am UT while on the 21st we have Io eclipsed in Callisto’s shadow after 3.10 am UT. Europa’s shadow eclipses Ganymede on the 24th after 6.20am UT while those with a new scope for Christmas might be able to enjoy Europa transiting Ganymede just after 1020pm UT. On the 30th we have another occultation between io and Europa beginning after 9.30pm UT. There are other events, this is just a selection of the best and look out for the smaller moons such as Amalthea which are visible in larger scopes, these smaller moons are being occulted and eclipsed regularly and it’s worth keeping an eye out for. Remember that these mutual events are an every 12 year event, so get out n enjoy them while you can
Next up for the planet hunters is Venus which as the month goes on climbs back into the evening sky after spending almost the entire year camped in the predawn sky. Early in the month it will be still low in the evening sky but as the month progresses we will see our cloud shrouded twin climb away from the Sun and take up residence in the evening sky. Not much to see telescopically though and I’ve always thought of Venus as more of a visual treat. Filters sometimes help to pull out a little cloud detail, but this may need to wait until Venus is higher and in darker skies.
As we fall into the last part of the month Venus is joined by Mercury for what could be a beautiful conjunction in the low evening sky, Venus shining away at -3.8 and below that close to the horizon will be mercury at -0.7. On the 23rd they are joined by a thin crescent moon. Grab yourself a good south western horizon, perhaps with some elevation and enjoy the inner planets over the Christmas and New Year week.
Uranus is still on show in Pisces and while getting more distant all the time it is still visible to the naked eye at magnitude 5.8. I you need help finding it the moon sails past at less than a degree just after midnight on the morning of the 2nd. Neptune in Aquarius is currently magnitude 7.9 and with Aquarius now in the southwest after sunset your observing time is short.
Mars is still hanging around like a jilted lover, low in the southwest after sunset in Capricornus it sits close to the moon on Christmas day if you want to test your freshly opened astronomy prezzies.
Saturn has made it around the back of the Sun from our perspective and is now returned to our skies as an early morning object for those desperate for a dose of ringworld. It is currently in Scorpius and can be viewed in the hour or so before dawn.
The Moon this month starts just beyond first quarter and we reach full moon on Saturday 6th at 12.27pm UT, last quarter is reached on the 14th at 12.52pm UT and New moon follows on 22nd at 1.36 am UT. Last quarter is achieved on the 28th at 6.32pm UT.
For the libration fans there is a good chance of catching Crater Rozhdestvenskiy on the night of the 10th. This is a rare libration target to bag as it sits right on the edge of what is possible to see with libration and is a farside crater, 110 miles across if you could see it face on it would be one of the larger impact craters, Plato, a large crater not too distant from Rozhestvenskiy is a lot smaller at only 68 miles across.
December is of course time for the Geminid meteor shower which is one of the better showers in the calandar with a ZHR bigger than the Perseids. It is perhaps less famous because of the time of year, the Perseids picking the warmer less cloudy time of the year to put on their show. The radiant will move past Castor in Gemini through the month with the radiant just next to Castor at the showers peak on the 14th. The peak is during the daylight for Europe so the best time to see the shower is in the early hours of the 14th. The moon isn’t perfect for this shower, but will have passed full so won’t drown out everything.
Comet wise despite the ubiquitous presence of Churyumov-Gerisimenko on the news at the moment we are in a bit of a drought with some faint comets available for the keen eyed and large scoped. Comet R1 Borisov is magnitude 11.1 in Virgo and slowly brightening, Comet Q3 Borisov is in Draco at magnitude 11 and fading while E2 Jacques which entertained us so well this year is in Aquila and is fast vanishing off of amateur levels of magnitude.
For our deep sky challenge this month we are going look at objects that are in or near Orion that aren’t the habit forming M42 or flame and horsehead nebulae. The area of sky around Orion is one of the skies most famous and always eagerly anticipated, but hidden around it are perhaps some of the most overlooked deepsky objects, drowned out by the clamour for perhaps the most famous objects in the sky.
First of all let’s start with two of the most ignored Messier objects on the list. M78 is in Orion just to the left of a line from Betelgeuse and Alnitak in the belt. This is an emission nebula that is also part of the Orion molecular cloud and is around 1600 light years away. You will see two stars with this cloud that are around magnitude 10 and are responsible for lighting up this cloud of dust.
Next we are dropping below Orion into the rarely viewed constellation of Lepus the Hare, the poor creature being chased by Orion’s dogs. Below the main body of the constellation you can find Messier 79 a globular cluster, unusual for the time of year as we mainly think of globs as a summer target and also a bit of an enigma as it is thought that M79 is not native to our galaxy and may have originally formed part of the disputed Canis Major dwarf galaxy. It is often described as starfish shaped and is magnitude 8 and 42,000 light years away.
We will now jump to the right of Orion and look at the constellation Eridanus, the river. It is a long indistinct constellation that fills the sky in the area to the right of Rigel. Here you can track down two nice targets in the form of planetary nebula NGC1535 which is a real challenge for observer and imager alike and will need patience and good skies, but you will be rewarded with a distinctive blue fuzzy disc. To begin your hunt start at the star Zaurak and move back towards Rigel and as Zaurak leaves your finder scope you are close. Now above 1535 is a nice multiple known as Keid which has celebrity status, for this is the home star of the planet Vulcan. Keid A is in fact very similar to our sun and must be a prime target for SETI, it has two faint companions B which is easily seen in a reasonable sized scope at low power and C which is much fainter and requires high magnification and a good clear sky.
For our last around Orion challenge we go back into the constellation itself but this time to the rarely visited club, the area of stars above Betelgeuse towards Gemini. Here you will find the Monkey Head Nebula NGC2174 and an associated cluster 2175. This is an Hii emission nebula 6,400 light years away and is magnitude 6.8.
So I wish you happy hunting and clear skies.
End of podcast:
365 Days of Astronomy
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