Hello? Is there anybody there? In the show this time, we talk to Tom Scragg about Pulsar timing arrays, Jonathan Wong rounds up the latest news, and we find out what we can see in the December night sky from Ian Morison, Haritina Mogosanu and Samuel Leske.
This month in the news: the Decadal Review, iodine propulsion and the launch of DART
Firstly in the United States, the decadal review, made by the national academies of science, engineering and medicine has been published. This is done by the board of physics and astronomy, usually around the start of a new decade, and outlines key proposals for what will be done in the future for astronomy.
The US as a country is the world's largest investor in astronomy, so this review is very important in shaping how the field progresses. To give a few examples, the review from the 1970s pushed for the construction of the Very Large Array. The 1980s review pushed for a space based advanced x-ray telescope which resulted in the launch of the Chandra x-ray observatory in 1999. The review in 2001 led to the construction of the James Webb Space Telescope.
The major proposal this time is for a large (6m diameter) space telescope in Infrared/Optical/Ultraviolet. The telescope would be able to perform imaging and spectroscopy with the sales pitch being that it could be used to detect biosignatures in habitable zone exoplanets. More broadly though, with recent missions giving astronomers large numbers of exoplanets found this telescope would be able to focus on interesting targets, giving more detailed spectra so we have a better idea of their composition.
The plan would be for this telescope to be planned later this decade, with an initial launch date in the 2040s.
Some of the other proposals in the decadal review include maintaining the Explorer program the creation of a ‘probe class’ of missions.
The Explorer program involves smaller, lower budget space missions. It is split into medium class, small and university class. They tend to be missions with a single or narrow focus, meaning they still produce high quality research at those budgets. For example both ACE (the advanced composition explorer) and WMAP (the wilkinson microwave anisotropy probe) are explorer medium class missions.
The previous decadal survey pushed for an expansion of the Explorer program, leading to more proposals and more successful launches. This decade one of the major proposals is to build on this program and in particular to keep the launch rate high for these smaller missions.
The idea for the ‘probe class’ comes from the review seeing a large gap between the medium class explorer missions and the major missions, what the review refers to as ‘large strategic missions’. This gap is rather obvious in terms of the finances and timescales, the largest medium explorer missions cost in the hundreds of millions (capped at $350 million) and there is nothing between that and Planck or JWST size missions.
The proposed probe class would have a funding cap like the explorer missions but larger, and aim for a launch every decade. Far more regular than the flagship telescope launches.
In other news a paper has recently been published reporting on the use of iodine as a way to propel small satellites. The key to this idea is that of electric propulsion, which works by first ionising a gas, then it is possible to accelerate those ions to produce thrust. Currently these systems use Xenon as their propellent, but as the authors point out, Xenon is rare, expensive to make and must be stored at high pressure.
Iodine has been proposed as an alternative many times before, it would eliminate the need for high pressure containment and is less rare than Xenon, however this is the first time an iodine propulsion system has been tested by performing manouvres in space.
The paper shows a test of an electric propulsion system using iodine as a propellant, detailing the construction of the system, which was built into a cubesat. Then describing tests of propulsion system on earth in a cryostat, before finally detailing a test of the system in orbit, with results both from on board telemetry and from being tracked by the US Sky Surveillance Network.
Some of the technical challenges this project faced include the electronegativity of iodine which was mitigated by using a polymer film coating on many of the parts and the use of technical ceramics such as zirconium oxide used to make some of the components. Also the potential problem of vibration breaking the initially solid iodine was solved by embedding the iodine in a ceramic block.
The paper demonstrates the cost savings from using iodine as the propellant, both in reducing the cost of the fuel itself but also reducing the cost of the hardware needed, mainly as iodine can be stored as a solid and sublimated, meaning no need for the high pressure containers used in xenon systems.
In future, this lower cost could enable more small scale missions to include propellant, as currently many cubesat missions do not. This means an opportunity for more interesting science results due to small, low cost satellite missions adding the ability to position themselves in space, and the ability to bring a far larger fraction of our small missions out of orbit, while currently most cubesat missions are left in space.
Finally, the DART mission was launched. DART, standing for Double Asteroid Redirection Test, is a mission to impact an asteroid in order to redirect its orbit.
The target is a binary asteroid system of Didymos and a smaller orbiting satellite, Dimorphos. The plan is to crash DART into Dimorphos and observe how it moves in response to the impact. As Dimorphos is orbiting Didymos we have a good knowledge of its orbit, in particular we know its current orbital period to an impressive degree of accuracy.
The reason for this experiment is because this method is a good way to prevent near earth objects from reaching earth. If one were to be on a collision course with earth we would want to force it away, however destroying the object could still be dangerous, replacing one large object with a large number of smaller fragments. The safe option would be to give a small kick to the asteroid, nudging its orbit while it is still a safe distance to the point that it is no longer a danger to earth, without causing it to break up unpredictably.
DART will let us test this idea in space on a system which is far away and on an orbit which does not intersect with earth.
The mission also includes the Light Italian CubeSat for Imaging of Asteroids. 10 days before impact this smaller satellite will separate from DART, and will use both a high resolution imager and a large field of view camera to record the impact.
Interview with Tom Scragg
Tom Scragg is interviewed about his work on pulsar timing arrays, in particlar eMerlin and DARA (Development in Africa with Radio Astronomy).
The Night Sky
Ian Morison tells us what we can see in the Northern Hemisphere night sky during December 2021.
- Jupiter As darkness falls at the start of December, Jupiter, having a magnitude of -2.29 and an angular size of 38.3 arc seconds, may be seen in the south. It transits at 17:15 GMT with an elevation of ~24 degrees. By month's end its magnitude will have reduced slightly to -2.13 and its angular size to 35.36 arc seconds and it will be seen in the south southwest at nightfall. Happily, this year Jupiter has climbed up the ecliptic somewhat so the atmosphere will not hinder our view of the solar system's giant planet as much as it has in the last two years.
- Saturn Saturn precedes Jupiter into the sky and will be seen towards the south southwest at nightfall. It then shines with a magnitude of +0.7 with its disk 16 arc seconds across and the rings spanning some 37 arc seconds. By month's end, it has a reduced brightness of magnitude +0.71 with a 15.46 arc second disk. Sadly, its elevation will only be about 17 degrees at as December begins so the atmosphere will hinder our view of this most beautiful planet.
- Mercury Having passed behind the Sun at the beginning of December makes an appearance after sunset in the last few days of the month very low in the southwest below Venus. It will have a magnitude of ~-0.73 and an angular size of ~6 arc seconds. Binoculars may well be needed to spot it, but please do not use them until after the Sun has set.
- Mars This month, Mars climbs out of the Sun's glare in the pre-dawn sky having a magnitude of 1.64 on the first with an angular size of 3.77 arc seconds. It will then be best seen at around 06:41 GMT in the southeast. By month's end the best time to observe it will be at ~07:00 GMT when it magnitude will have increased slightly to 1.54 with an angular size of 4 degrees. Binoculars may well be needed, but please do not use them after the Sun has risen.
- Venus At the start of December, Venus, at magnitude -4.87 and having an angular size of ~39 arc seconds, will only have an elevation of ~8 degrees at sunset looking towards the south southwest. It may well be lost in the Sun's glare until around 16:00. During the month it falls back towards the Sun and will be lost in the Sun's glare. As the ecliptic is at a shallow angle to the horizon in the latter part of the year, it has never got to a high evening elevation during this apparation.
Highlights of the Month
- December, evening: the Double Cluster and the 'Demon Star', Algol. This month is a good time to look high in the southeast towards the constellations of Cassiopea and Perseus. Perseus contains two interesting objects; the Double Cluster between the two constellations and Algol the 'Demon Star'. Algol in an eclipsing binary system as seen in the diagram below. Normally the pair has a steady magnitude of 2.2 but every 2.86 days this briefly drops to magnitude 3.4.
- December: find M31 - The Andromeda Galaxy - and perhaps M33 in Triangulum. In the late evenings when the Moon is not prominent, the galaxy M31 in Andromeda will be visible high in the southeast. The chart provides two ways of finding it:Around new Moon (3rd December) - and away from towns and cities - you may also be able to spot M33, the third largest galaxy after M31 and our own galaxy in our Local Group of galaxies. It is a face on spiral and its surface brightness is pretty low so a dark, transparent sky will be needed to spot it using binoculars (8x40 or, preferably, 10x50). Follow the two stars back from M31 and continue in the same direction sweeping slowly as you go. It looks like a piece of tissue paper stuck on the sky just a bit brighter than the sky background. Good Hunting!
- December - still worth observing Jupiter. This is still not a bad month to observe Jupiter which will be visible in the south after sunset. It lies in the southern part of the ecliptic and, sadly, will only reach an elevations of ~22 degrees when crossing the meridian. An interesting observation is that the Great Red Spot appears to be diminishing in size. At the beginning of the last century it spanned 40,000 km across but now appears to be only ~16,500 km across - less than half the size. It used to be said that 3 Earths could fit within it, but now it is only one. The shrinking rate appears to be accelerating and observations indicate that it is now reducing in size by ~580 miles per year. Will it eventually disappear? The features seen in the Jovian atmosphere have been changing quite significantly over the last few years - for a while the South Equatorial Belt vanished completely (as seen in Damian's image) but has now returned to its normal wide state. The diagram on right shows the main Jovian features as imaged by the author at the beginning of December 2012.
- December: find Uranus. This month is a still a good time to find the planet Uranus in the late evening as it reached opposition on November 4th. With a magnitude of 5.7, binoculars will easily spot it and, from a really dark site, it might even be visible to the unaided eye. A medium aperture telescope will reveal Uranus's 3.7 arc second wide disk showing its turquoise colour. It lies in Aries, close to the boarder of Cetus as shown on the chart. A highlight below shows when it lies just above the Moon so making it easy to find.
- December 6th - after sunset: Three Planets and a crescent Moon. If clear after sunset on the 6th, there will be lovely line up of Jupiter, Saturn and Venus along with a very thin crescent Moon. Binoculars may well be needed to cut through the Sun's glare, but please do not use them until after the Sun has set.
- December 8th after sunset: - Jupiter, Saturn and the Moon. If clear after sunset on the 6th, one could observe the Moon lying below Jupiter and Saturn.
- December 14th - evening: - Uranus above the Moon. If clear in the evening of the 14th, Uranus could be spotted lying up to the left of the Moon.
- December 16th - late evening: the Moon below the Hyades and Pleiades Cluster. If clear in the late evening of the 16th, the Moon will be seen to lie just below the Hyades and Pleiades clusters.
- 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. This year, the Moon will be moving towards third quarter so, sadly, its light will 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 31st - before dawn: Mars and the Moon. If clear and given a low horizon towards the southeast, Mars should be visible down to the left of a very thin waning crescent Moon.
- December - Evenings of the 12th and 26th: The Straight Wall. The Straight Wall, or Rupes Recta, is best observed either 1 or 2 days after First Quarter or a day or so before Third Quarter. To honest, it is not really a wall but a gentle scarp - as Sir Patrick has said "Neither is it a wall nor is it straight!"
Haritina Mogosanu and Samuel Leske from the Carter Science Centre in New Zealand speaks about the Southern Hemisphere night sky during December 2021.
In the southern hemisphere it is summertime but everything else is the same, we too are preparing for Christmas and to celebrate the anniversary of Apollo 8 - the first people to ever go around the Moon on Christmas Day 1968.
Speaking about the Moon, this month, the New Moon is on the 4th of December - this is when it is great to go deep-sky observing. First quarter is on the 11th of December - which means the Moon is in the sky in the first part of the night, and is setting after midnight. Full Moon occurs on the 19th of December - we hope you like long walks under the moonlight, because no deep sky objects will be easily visible in the sky as full Moon does make light pollution, and you will use a moon filter if you want to observe the Moon. And finally last quarter on the 27 of December, which means the Moon is in the sky in the last part of the night so rising after midnight. This is very helpful to plan your stargazing accordingly.
Venus, Saturn and Jupiter are beautifully aligned at sunset and visible at the beginning of the month just after sunset. Venus is the closest to the horizon followed by Saturn and then Jupiter. Towards the end of the month, Venus will get too close to the Sun, Neptune and Uranus are visible all night long. Mars is in Libra and moving into Scorpius by the end of the month, which means it will be visible in the morning sky then.
I often get comments like, who can remember oh, so many stars, or is it really hard to remember all those constellations and so on. While this is true, many cultures - we all know that, invented stories about different stars in the sky and that made things easier to remember. Some cultures, in particular, had seasonal asterisms, and some of these asterisms encompassed the entire sky. How to remember all of it? Is by linking to things that are memorable or make your own stories!
With that in mind, let’s look at the sky in December in New Zealand.
December is very famous for Christmas and Christmas is very famous for Christmas trees. As I was learning the south celestial night sky, one night it occurred to me that right now in December, the entire region of the south celestial pole looks like a giant Christmas tree. Of course I am biased, and I love Christmas trees as well, but this trick helped me remember where everything was. Let’s look at that patch of the sky.
The sky looks like a Christmas tree only in December, just after sunset, if you look at the southern part of the sky. I will start at the top with Achernar, we can give that magical tree topper function.
Is very high in the sky about 75 degrees from the horizon. Then, just a bit lower down, the Magellanic Clouds are like two patches of snow one third town the tree and at the base, Look under the Southern Cross, those two stars, Gamma Centauri (Muhlifain) and Delta Centauri, together with the Southern Cross and Musca are the trunk.
All the other stars in Centaurus and Vela are decorations on the lower branches. Can you see the giant celestial Christmas tree? We might not have snow this time of the year in the Southern Hemisphere but it is like nature compensated for that with a celestial Christmas Tree just in time for Christmas.
Then, in the North, the Great Square of Pegasus – is the only horse that looks like a square and one of the very few northern constellations that is not upside-down.
Pegasus pulls a sleigh – we can make that up out of the Pleiades, Hyades and Orion. Draw a line between these asterisms and you can see the sleigh. Orion is the back of the sleigh where the driver sits and the Pleiades is the front where the runners are curved. Can you see the sleigh? We don’t have reindeers in New Zealand so Pegasus the flying horse will have to do.
Running behind the sleigh, on the ground , is a Dog - this is the Dog Star, Sirius. He’s very happy on the snowy road, which is the Milky Way. We can imagine that the sleigh has just come up from behind the Christmas tree and is flying across the sky to the Northern Hemisphere. But there’s one more star, my favourite star here, Canopus. I call this the Cat Star as every Sirius astronomer in New Zealand who wants a cat should contemplate this name first.
Halfway through from the top of the Christmas tree which is the star Achernar, our cat, Canopus jumps to catch the back of the sleigh. By the looks of it, it will probably land on the dog.
So we can turn the night sky in December, in New Zealand into a big Christmas Scene. We have a horse, sleigh, and a big Christmas Tree.
Draw a line from Sirius to Canopus – which are two very bright stars, it will lead you to the Magellanic Clouds. Sirius is in fact the brightest star in the sky, Canopus is the second brightest star in the sky and to the right of the imaginary Christmas Tree is Alpha Centauri, the third brightest star in the sky.
Lower on the Northern horizon, underneath the galloping hind-legs of Pegasus, Andromeda Galaxy is a smidge of light. It is the furthest object we can see with the naked eye, 2.5 million light years distance from us. When the light that we see now from Andromeda left the galaxy, on Earth, some of our hominid ancestors, facing food shortages, developed larger brains, as an evolutionary strategy. This led to the genus Homo, which first arose 2.5 million years ago. Homo habilis developed as the ice ages began, a time known as Pleistocene. And who knows, maybe the first human memories of winter too.Some cool binocular objects this month lay low around the horizon. Best objects to start with are obviously the Moon, the planets and double Stars (Alpha Centauri, Gamma Velorum, Beta Muscae and Upsilon Carinae, The Pleiades and Andromeda Galaxy are all great binocular targets. Then, of course, the Magellanic Clouds are great to look at. Some favourites of ours are visible in the night sky in December. The first of these is M74 which is vey hard to see due to its very low surface brightness. With very dark skies it can be seen from the Wairarapa, you’d need Bortle Scale 2 or 1 to see it. 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.
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 a large spiral galaxy at an angle to us so it looks like an elongated ellipse. It’s relatively bright and easy to spot if 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 and appears about 27 arc minutes 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 grey 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.
At this time of the year the two galaxy groups of the Fornax Cluster and the Grus Quartet are also in a good position for viewing. As the month advances the position of the Fornax Cluster improves and the position of the Grus Quartet gets worse so get in early to see these four stunning galaxies. Both groups are between 60 Mly and 80 Mly distant with the Grus Quartet being three galaxies visually quite close to each other and another galaxy a little further away. With the right eyepiece you can get all four in the same field of view. With the Fornax Cluster it is possible to get up to 11 galaxies at once in the same field of view. These are mainly elliptical galaxies including the stunning Fornax A.
December in the Southern Hemisphere is generally the unhappy month for the astronomer, unless your thing is solar astronomy, because the nights are short and the temperatures are creeping up. It seems to take forever for the night to get truly dark and forever for the telescope to cool down. Unlike the rest of the population, us astronomers are craving a cold front to blow through and give us a nice cool patch of air to settle the thermals and give us some great seeing. The good news is that this time of year is perfect for an all nighter of astronomy (all 4.5 hours of astronomical night) as the Milky Way passes through the zenith in the early hours and there’s a wealth of deep sky objects to fill your eye piece.
Due East – Taurus Orion region
A good place to start an evening’s viewing is Orion, that majestic constellation that is easy to find in the Northeast at about 35 degrees in elevation. With a pair of binoculars an observer can easily see the Great Orion Nebula (Messier 42 or M42) which is a huge star forming region just above Orion’s Belt, which is made up of the three stars of Alnitak, Alnilam and Mintaka. Mintaka is very dear to navigators as it’s located exactly on the celestial equator.
Orion has a number of very interesting stars including Betelgeuse which is a red supergiant and one of the largest stars in the sky. It is one of the few stars that have been imaged and it’s unusual shape is quite apparent showing it probably has a very unstable atmosphere causing the asymmetric bulging of the star. Because of its massive size Betelgeuse will not live for much longer – maybe only another 1000 years. Or it may have already exploded! But given its 400 or so light years away we might not find out for a while. When it does go it will create quite a spectacle on Earth as it will be a very bright supernova and will probably even be visible in daylight.
M42 is relatively close to us at about 1400 light years which makes it one of the brightest nebulae in the sky. With a telescope the M42 can appear to have a greenish tint, unlike the bright red photos that are often published. It is estimated that M42 is about 24 light years across and that it is part of a much larger structure known as the Orion Molecular Cloud, which extends for about 10 degrees across the whole constellation of Orion. This cloud includes the famous Horse Head Nebula (B33), Flame Nebula (NGC 2024), M78 and Barnards Loop (Sharpless 2-276). If you have access to an infrared telescope, you can also see the brightest object in infrared, that is the Becklin-Neugebauer object. M42 is one of the most photographed objects due to its brightness and visibility in both the Northern and Southern Hemispheres.
These are some of my favourite things about December, other than sleigh bells and snowflakes and warm woolen mittens and from here from New Zealand,
I wish you clear skies so that you can always see the stars and always remember we are made of the same star dust as they are.
Odds and Ends
The James Webb Space Telescope's launch has been delayed following an incident while setting up for launch. The telescope, a USD $10 billion successor to the Hubble Space Telescope, had recently been transported to Kourou in French Guiana to be launched at their spaceport, ahead of a planned launch on 18th December 2021. However, it was announced in late November that a sudden, unplanned release of a clamp band" had resulted in vibrations in the telescope, and the launch was delayed to allow for inspection to ensure there were no issues with the telescope's ability to operate. At time of recording, the telescope's launch had been rescheduled for the 22nd of December; however, unrelated issues with the telescope's communication system have now delayed the launch until the 24th of December at the earliest.
The 29th of November marked the anniversary of Australia's first satellite in space. The satellite made Australia the 7th nation to reach space unmanned.
|Interview:||Tom Scragg and Michael Wright|
|Night sky:||Ian Morison and Haritina Mogosanu|
|Presenters:||Fiona Porter and Mariam Rashid|
|Editors:||Michael Wright, George Bendo and Thomas Rennie|
|Segment Voice:||Tess Jaffe|
|Website:||Michael Wright and Thomas Rennie and Stuart Lowe|
|Producer:||Michael Wright and Thomas Rennie|
|Cover art:||In early March, testing teams deployed Webb’s 21 feet 4-inch (6.5 meter) primary mirror into the same configuration it will have when in space. Like the art of origami, Webb is a collection of movable parts that have been specifically designed to fold to a compact formation that is considerably smaller than when the observatory is fully deployed or extended. CREDIT: Northrop Grumman|