In the show this time, we talk to Dr. Jason McEwen about next generation radio telescopes, Ian and Fiona round up the latest news, and we find out what we can see in the September night sky from Ian Morison and Claire Bretherton.
The News
A new set of rumours appeared this month, with many suggesting that an important new discovery has been made in the field of gravitational wave astronomy.
The two gravitational wave events so far confirmed by the LIGO team have been hugely important, but both apparently come from only one of the potential classes of gravitational wave events -- that of black hole-black hole collisions.
The potential new discovery is an entirely new type of event: gravitational waves from a collision involving a neutron star.
Black hole-black hole collisions are extrememly violent events, but, depending on how much other matter is in the vicinity, they may be expected to stay dark, releasing no flash visible in the electromagnetic spectrum. However, Neutron Stars -- remants of large stars consisting solely of neutrons held apart by the Pauli exclusion principle -- are both small and dense enough to produce an appreciable gravitational wave signal, but are also expected to be far more likely to produce emission visible in the electromagnetic spectrum by more traditional telescopes.
These flashes, often referred to as 'optical counterparts', can still be difficult to associate with gravitational wave events, as LIGO's interferometers are very ppor at working out which direction a gravitational wave has come from. This can be helped however by detecting gravitational waves in multiple detectors placed around the world. allowing the source's origin to be triangulated. The recent addition of the newly upgraded VIRGO gravitational wave interferometer to LIGO's arsenal means the collaboration can now do just that, and provide a much smaller region of the sky for the small army of electromagnetic telescopes, across the spectrum, which give up some of their time to respond quickly to gravitational wave detections, spin round, and look for optical counterparts in that part of the sky.
After a tweet from J Craig Wheeler of the University of Texas on the 18th of August, reading: "New LIGO. Source with optical counterpart. Blow your sox off!" (that's sox with an x), intrepid astronomer's did some digging and appeared to find exactly this process taking place.
The Hubble, DECam, and VLT optical and infrared telescopes; Chandra X-ray telescope; Fermi Gamma Ray telescope; and ALMA submillimetre telescope all appear to have made observations in the same direction at some point in the period from the 18th to the 22nd of August -- in the direction of the galaxy NGC4993, some 40 Mpc away. This appears to fit with what would be expected for a coincident detection of a Gamma Ray Burst and gravitational wave event, expected from a collision of two neutron stars. In addition, several of the observations have suspicious looking publice names -- the Hubble observation being labelled as 'BNS Merger' -- BNS being a common acronym for binary neutron star.
There has currently been no official statement on the rumour from the LIGO and Virgo collaboration, who did release this statement on the 25th of August, to coincide with the end of their most recent period of science observations:
"Some promising gravitational-wave candidates have been identified in data from both LIGO and Virgo during our preliminary analysis, and we have shared what we currently know with astronomical observing partners. We are working hard to assure that the candidates are valid gravitational-wave events, and it will require time to establish the level of confidence needed to bring any results to the scientific community and the greater public. We will let you know as soon we have information ready to share."
J Craig Wheeler also tweeted again on the 23rd of August with a mea culpa, apologising for the earlier tweet and stating "LIGO deserves to announce when they deem appropriate".
If an announcement is made soon, it will be a fantastic next step in the opening up of gravitational waves as a way to observe the Universe.
Also in the news this month were the celebrations of the 40th anniversary of the launches of the two Voyager spacecraft.
Launched on the 20th of August and 5th of September 1977 by NASA, Voyager 1 and Voyager 2 have been pioneering and unique missions to the outer solar system. In the intervening decades the Voyager probes, carrying their famous gold disc records of information about life on Earth for any potential extraterrestrial life to find, have sent back a wealth of information and awe-inspiring images of our solar system.
In 1979 Voyager 1 (which was actually the second of the two to be launched) sent back pictures of Jupiter, settling a centuries-long argument about the direction of spin of the great red spot storm. The probe then moved on to the moons, including Io where the first volcanoes outside of Earth were discovered. In the 80s, the first (and so far only) visits to the outer giant ica planets of Uranus and Neptune were made by Voyager 2, who discovered that Uranus is spinning on its side, and Neptune has its own giant storm, with 2,500 mph winds. By 1990, both probes had been directed up and out of the ecliptic plane of the solar system, allowing them to send back a 'family portrait' of all the planets in the solar systema s seen from above, including the famous 'pale blue dot' image of Earth from 6 billion kilometers away.
The two probes have since become famous for being so far away, including continual chatter about exactly where the 'edge' of our solar system should be defined and exactly when the probes can be said to have left. What is known for sure is that they are both still communicating with us, with measured distances of 2.08x10^10 km and 1.72x10^10 km as of July 2017.
Since last year the gyroscopes have been turned off and we can no longer control the path of the probes, and science instruments will gradually be shut off over the next five years, with the final communications expected to happen some time between 2025 and 2030.
And finally a new image of the star Antares was revealed this month, which shows the most detailed picture ever seen of a star other than the sun.
By using the Very Large Telescope Interferometer (or VLTI) located in Chile, astronomers from the European Southern Observatory.
Antares is a red supergiant star in the constellation of Scorpius 550 light years away, and was imaged by the team to a resolution of around 5 milliarcseconds -- that is 1/360,000 the diameter of the moon on the sky.
The astronomers did not just make a pretty picture. By making the images at multiple infrared wavelengths, they were able to make a map of speeds of gases flowing around the star, an important step in understanding the unexpectedly turbulent motions of old and dying stars like Antares.
Interview with Dr. Jason McEwen
Dr Jason McEwen is from the Mullard Space Science Laboratory (MSSL) at University College London (UCL). His fields of research are in astrostatistics and astroinfromatics applied on large astrophysical data sets. In this interview, he is talking about his work on statistical and mathematical analysis techniques using wavelets applied on radio interferometric data and how these techniques will be useful for the future SKA project.
The Night Sky
Northern Hemisphere
Ian Morison tells us what we can see in the northern hemisphere night sky during September 2017.
The Planets
- Jupiter: Now five months after opposition, Jupiter can still just be seen very low in the southwestern sky after nightfall, lying at an elevation of some 10 degrees 45 minutes after sunset. By month's end it will be at an elevation of just 4 degrees at dusk. With a magnitude of -1.7 and an angular size of ~31 arc seconds it will be at its dimmest and smallest during this year's apparition and is too low for any reasonable telescopic views. At the start of September, Spica, Alpha Virginis, lies some 4 degrees to its lower left. Jupiter, moving eastwards passes 3 degrees to the upper right of Spica on September 11th. Now moving down towards the lower part of the ecliptic, next year it will only have an elevation of 25 degrees when due south whilst for the following two years an elevation of just 18 degrees.
- Saturn came into opposition back on June 11th and so will be seen in the southwest as darkness falls and sets late evening. It shines initially at magnitude +0.4 falling to +0.5 during the month and has an angular size of ~16.5 arc seconds. With an angle of 26.8 degrees inclination to the line of sight, the rings are virtually as open as they ever can be. Their maximum tilt, at 27 degrees, will come in October - the first time since 2002. It is sad that Saturn, now lying in the southern part of Ophiuchus between Sagittarius and Scorpius, only reached an elevation of ~17 degrees above the horizon when due south, so hindering our view of this most beautiful planet. If imaging Saturn (or Jupiter), Registax 6 has a tool to align the red, green and blue colour images to largely remove atmospheric dispersion from the image. At somewhat over £100 one can purchase the ZWO atmospheric dispersion corrector which uses two, contra rotating, prisms to carry out an even better correction - and which can also be used for visual observing.
- Mercury. has now become a morning object and will form a very tight grouping with Mars and Regulus, in Leo on the morning of the 5th. They will lie about 15 degrees below Venus. Binoculars will be needed to observe them in the bright twilight but please do not use them after the Sun has risen. Rising in elevation during the first part of the month, by the 10th it will have brightened to zero magnitude and lie just half a degree to lower right of Regulus. Mercury reaches greatest elongation, some 18 degrees from the Sun on the 12th - its best morning apparition this year. On the 14th, it lies 11 degrees to the lower left of Venus whilst, before dawn on the 16th, it closes to just 0.3 degrees from Mars. In the final week of September, moving back towards the Sun, it will be lost in the Sun's glare. .
- Mars has now become a morning object at the start of its new apparition. Lying in Leo, and still not easily seen in the pre-dawn sky, it forms a tight grouping with Mercury and Regulus on the 5th some 15 degrees to the lower left of Venus. During the month, Mars has a magnitude of 1.8 and an angular size of just 3.6 arc seconds so no details will be seen on its salmon-pink surface. As the month progresses Mars rises higher in the sky before dawn and moves closer to Venus which is now moving back towards the Sun
- Venus is visible in the east before dawn this month, rising around 2 hours before sunrise. Its magnitude remains at -3.9 during the month as its angular diameter shrinks from 12.4 to 11.2 arc seconds. However, at the same time, its illuminated phase increases from 84 percent to 91 percent - which explains why its magnitude does not change.
- Saturn: After what felt like a long, cold, wet winter here in Wellington, September marks the start of spring in the southern hemisphere. As we head towards the equinox on the 23rd of the month we see a rapid change in our daylight hours, with our days getting longer and our nights shorter. Equinox means "equal night" because we have the same number of hours of daylight and the same number of hours of darkness at this time of year. By the end of September the Sun won't be setting until nearly half past 7.The mission has revealed the complexity of Saturn's ring system, identified numerous new moons, and provided some of the most stunning images of the solar system that we have ever seen. It has found liquid oceans and a thick atmosphere on Titan, with conditions that may be similar to early Earth, and exploration of the icy moon Enceladus has revealed a hot spot at the southern pole, icy jets spewing out from the surface and a vast ocean below the ice.
- Neptune: Whilst there are only two evening planets you can see with your own eyes, Neptune is also in our evening skies, with Uranus joining it before 10pm. Both can be picked out with binoculars, and you may even notice a greenish colour to Uranus, but Neptune will be indistinguishable from a faint star.Now is the best time to look for the eighth planet though, as it reaches opposition on the fifth of the month, when it will be directly opposite the Sun in the sky and at its highest in the north at midnight. At around this time the planet will also be at its closest and brightest, shining at magnitude 7.8, and is sat less than a degree just below and to the right of the 3.8 magnitude star lambda aquarii, but you'll still probably need a detailed finder chart to spot it. Unfortunately, the full moon passes close to Neptune just after opposition, so it may be easier to find a week or two later.
Highlights of the Month
September - Find the globular cluster in Hercules and spot the 'Double-double' in Lyra: There are two very nice objects to spot with binoculars in the south-eastern sky well after dark this month. Two thirds of the way up the right hand side of the 4 stars that make up the 'keystone' in the constellation Hercules is M13, the best globular cluster visible in the northern sky. Just to the left of the bright star Vega in Lyra is the multiple star system Epsilon Lyrae, often called the double-double. With binoculars a binary star is seen but, when observed with a telescope, each of these two stars is revealed to be a double star - hence the name!
September - A good month to observe Neptune with a small telescope. Neptune comes into opposition - when it is nearest the Earth - on the 2nd of September, so will be well placed to spot this month. Its magnitude is +7.9 so Neptune, with a disk just 3.7 arc seconds across, is easily spotted in binoculars lying in the constellation Aquarius as shown on the charts. It rises to an elevation of ~27 degrees when due south. Given a telescope of 8 inches or greater aperture and a dark transparent night it should even be possible to spot its moon Triton.
September 5th - before dawn: Mars Mercury and Regulus. Before dawn on the 5th, Mercury and Mars will be seen in a close grouping with Regulus in Leo. A very low eastern horizon will be needed to spot them with the use of Binoculars - but please do not use them after the Sun has risen. [The magnification given by the binoculars reduces the effective brightness of the pre-dawn light.]
September 12th - before dawn: the Moon closes on the Hyades Cluster. Before dawn on the 12th, the Moon will be seen closing onto the Hyades Cluster in Taurus.
September 16th - before dawn: three planets below the Moon. Before dawn on the 16th, a thin crescent Moon will be seen high above Venus, Mars and Mercury. Regulus lies between Venus and Mercury.
September 26th - after sunset: Saturn below the crescent Moon. After sunset on the 26th, Saturn will be seen lying below the Moon.
September: 12th and 28th: 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 28th the dark crater Plato and the young crater Copernicus will come into view. This is a very interesting region of the Moon!
Southern Hemisphere
Claire Bretherton tells us what we can see in the southern hemisphere night sky during September 2017.
Kia ora and welcome to the August Jodcast from Space Place at Carter Observatory in Wellington, New Zealand.
The Planets
Stars
The bright stars Vega and Canopus mark north-south around dusk this month, guiding our eye to the bright band of the Milky Way passing high overhead. Along with the nearby bright stars of Deneb, in Cygnus the swan, and Altair, in Aquila the eagle, Vega forms part of the "winter triangle" as seen here in the southern hemisphere.
To the south-east of Capricornus is the faint constellation of Piscis Austrinus, the southern fish, with its only bright star, Fomalhaut, marking the mouth of the fish. Fomalhaut is the 18th brightest star in the night sky, and the only, lonely bright star in its vicinity.Follow up observations, however, failed to confirm the planet and left many doubting its existence. It took until 2012 before Fomalhaut b was independently detected and confirmed. Its controversial past has earned it the nickname "the zombie planet", a planet resurrected from the dead.
Wishing you clear skies from the team here at Space Place at Carter Observatory.
Odds and Ends
When Hurricane Harvey hit Texas, it also affected the
Asteroid 3122 Florence (after Florence Nightingale) will be making its closest approach to the Earth on Sept 1st at 11.07 GMT. Florence is 4.4 km in diameter and will pass by the Earth at a distance of 7 million km (18 times distance between earth and moon). It is the largest object to come this close to the Earth since NASA started monitoring asteroids. It has a diameter of about4.5 km (for reference, the asteroid that wiped out the dinosaurs was about 15 km wide), and orbits the sun once every 2 years and 4 months. Asteroids like Florence usually live in the asteroid belt (between Mars and Jupiter), but sometimes resonance with Jupiter nudges them towards the sun. When Florence passes by the earth, astronomers will be able to look closely at it and learn more about it, like what shape it is and whether it has any moons. Amateur astronomers with access to small telescopes can also keep an eye out for Florence, which will be travelling upwards in the eastern sky all this week, through the two small constellations Equuleus and Delphinus (if you can't find those easily, look for them between Vega and the eastern horizon).
Show Credits
| News: | Ian Harrison and Fiona Healy |
| Interview: | Dr. Jason McEwen and Jean-Francois Robitaille |
| Night sky: | Ian Morison and Claire Bretherton |
| Presenters: | George Bendo, Fiona Healy |
| Editors: | Damien Trinh, Tom Scragg, Charlie Walker |
| Segment Voice: | Iain McDonald |
| Website: | Charlie Walker and Stuart Lowe |
| Producer: | Charlie Walker |
| Cover art: | The Voyager Golden Record! CREDIT: NASA, via Wikimedia Commons |
