Captured. This month, we continue our feast of interviews from the National Astronomy Meeting. We talk to Dr Patrick Sutton about gravitational wave detection with LIGO, Dr Antonio Chrysostomou and Dr Mark Thompson tell us about the sub-millimetre camera SCUBA-2, and Professor James Dunlop brings us up to speed on sub-millimetre galaxies and the instruments used to observe them. Megan rounds up the latest news and we find out what's in the June night sky from Ian Morison and John Field.
In the news this month:
Solar flares are energetic but short-lived eruptions in the atmosphere of the Sun. Most of the time they barely affect the Earth, but occasionally one heads in our direction and is strong enough to cause aurorae and affect satellites. Some stars have been observed to produce flares which are much more energetic but, up to now, very few so-called superflares have been detected on solar-type stars, making detailed studies impossible. Now, using the enormous amount of data collected by the Kepler satellite, a team of researchers led by Hiroyuki Maehara at Kyoto University has carried out a study of 365 superflares, on 148 solar-type stars, making meaningful statistical studies of the phenomenon possible for the first time.
The most energetic flare on record from our own Sun is known as the Carrington Event, which occurred in 1859 and left a detectable trace in polar ice cores on the Earth. But even this event was ten times weaker than the weakest superflares observed on other stars, some releasing 10,000,000 times as much energy as the Carrington Event. Polar ice cores show no evidence of stronger flares from the Sun over the last 2000 years, while the Kepler data show that, for the sample of stars in the survey, a superflare occurs on a solar-type star once every 350 years on average. The data also show that superflares occur less frequently on slower-rotating stars, and more often on cooler stars. Brightness variations in the stars which displayed superflares also suggest that they have much larger sunspots than our Sun. Since sunspots and starspots store magnetic energy, the superflares can be explained by large regions of starspot activity. Faster-rotating stars display more active magnetic fields and are generally younger than slower-rotating stars, and these results suggest that superflares occur more frequently on fast-rotating solar-type stars that are younger than the Sun. Superflares on stars similar in age to the Sun occur less frequently, but release similar amounts of energy.
Aside from sunspot activity, one other theory for the cause of stellar superflares is the magnetic interaction of the star with a so-called "hot Jupiter", a large gas giant in orbit very close to the star. However, these new results from the Kepler data suggest that such a mechanism is unlikely since, despite looking, not a single exoplanet has been found orbiting any of the 148 stars which displayed superflares. Kepler makes accurate measurements of stellar brightnesses, looking for the characteristic dimming caused by a planet passing between us and the star, but not every exoplanet will pass directly in front of its host star from our perspective. On average, if a planet exists in orbit around a particular star, the probability of a transit is about 10% (averaged over all possible orientations of the planet's orbit); so, if hot Jupiters were responsible for the flare activity seen in this survey, Kepler ought to have detected around 15 of them. Since none was found, it seems that superflares caused by planetary interactions are rare.
Over the last couple of years, images from the High Resolution Imaging Science Experiment (HiRISE) on board the Mars Reconnaissance Orbiter have shown many spectacular features of the Martian surface, including clear evidence of wind erosion, sand dune formation and seasonal avalanches. Now, in a paper published in Nature on the 17th of May, a team led by Nathan Bridges of The Johns Hopkins University has found evidence for the ongoing large-scale migration of sand dunes, not too different to dune migration seen on the Earth.
Mars has a much thinner atmosphere than the Earth, so high-speed winds (needed for the surface movement of material) are much less frequent and generally weaker than on our own planet. Sand dunes on the Earth are seen to migrate, with the entire volume of a dune being overturned as the wind blows the sand along. Although sand dunes have been known about on Mars since the days of the Viking spacecraft, it has long been debated whether they are currently active, or relics left over from a time when the atmosphere of Mars was thicker and the winds stronger. Now, images of a region known as Nili Patera, taken three years apart, have shown evidence that entire dunes, some as thick as 60 metres, are migrating across the surface of the planet at rates not much slower than those measured in some dune fields on the Earth. This result is surprising, since the wind speeds measured by landers on Mars rarely reach high enough to initiate the large-scale transport of sand. One solution is that local small-scale topography may be able to generate sufficiently large localised winds; another factor is the lower gravity of Mars, meaning that, once particles are lifted by the wind, they stay airborne more easily than on the Earth. Another surprising result is that the formation time scale for these dunes is much shorter than the time scales of climate fluctuations on the planet, implying that these dunes are not relics from a time when Mars had a thicker atmosphere, but that they could have formed under current climatic conditions.
There are, of course, many questions left to be answered, not least whether the level of activity seen in the Nili Patera region is typical of dune regions on Mars, or whether it is unusually active. Further studies of other regions on Mars, utilising the same careful image comparison techniques used by this team, should help to answer some of these questions.
And finally: After many years, several meticulous site surveys and thousands of pages of detailed reports, Friday the 25th of May saw the long-awaited result of the site selection process for the world's largest radio telescope, the Square Kilometre Array. And, rather than having one single location, the telescope will now be split across two continents.
After an initial international call for bids to host the telescope, the options were eventually narrowed down to two sites: Southern Africa and a joint bid by Australia and New Zealand. In both cases, the core of the telescope (consisting of a large proportion of the total number of antennas) would be constructed in a remote location away from man-made interference such as radio, television and mobile phone signals, with other groups of antennas built at a number of locations spanning distances of several thousand kilometres.
The project will be the largest radio astronomy facility on the planet and will ultimately consist of three different types of antenna, each covering a different part of the radio band. The dual-site option, selected by the SKA's international board, involves building different types of antenna in the two different locations which, since the different technologies will operate independently, makes use of the existing infrastructure at the two candidate sites where precursor telescopes have already been under construction for a couple of years. The first phase of the project, SKA1, will see 180 dishes added to South Africa's MeerKAT precursor telescope, forming a telescope with a narrow field of view but high sensitivity, while 60 dishes will be added to ASKAP, the Australian precursor, forming an array with a wider field of view but lower sensitivity and designed to carry out fast surveys of the sky, as well as many thousands of dipole antennas distributed over the Australian site and forming an array working at low frequencies. By incorporating the existing precursor instruments, the completed SKA1 will have greater capabilities than originally planned. The decision was welcomed by both of the bidding countries, although some onlookers have raised concerns over cost increases that may be incurred by constructing a dual-site telescope. However, due to the existing infrastructure at both sites, and the need for separate cores for each of the components, operating across two sites will add no more than 10% to the projected cost of phase one according to John Womersley, chair of the SKA Board of Directors. For phase two of the construction, expected to be completed around 2024, all the dishes and the mid-frequency aperture arrays will be built in Southern Africa, while the low-frequency antennas for phases one and two will be built in Australia.
Interview with Dr Patrick Sutton
Dr Patrick Sutton, from Cardiff University, works on gravitational wave detection with LIGO. LIGO is part of a network of ground-based interferometers looking for the tiny ripples in space known as gravitational waves, which are believed to exist all around us. Its two sites each host L-shaped vacuum tubes of several kilometres in length, along which laser beams are split, reflected back and forth repeatedly and finally recombined to produce destructive interference at a detector.
Dr Sutton explains how gravitational waves can change the interference pattern and so be detected, even when they alter the length of an interferometer tube by only one thousandth of the diameter of a proton. He talks about the sorts of cosmic events which should produce detectable waves, the way in which detection techniques have already been tested and how various interferometers all over the world will corroborate each other's measurements. These measurements will be complementary to those of pulsar timing arrays and future space-based interferometers, as these projects will observe gravitational wave of different frequencies. Dr Sutton explains how they will, collectively, allow astronomers to probe deeper into dark and energetic events within the Universe.
Interview with Dr Antonio Chrysostomou and Dr Mark Thompson
Dr Antonio Chrysostomou, from the Joint Astronomy Centre in Hawaii, and Dr Mark Thompson, from the University of Hertfordshire in the UK, work with the SCUBA-2 instrument, which is mounted on the James Clerk Maxwell Telescope. It is a bolometric camera, placed high up in the dry air of Mauna Kea in order to receive submillimetre electromagnetic wavelengths that are largely absorbed by water in the Earth's atmosphere.
Dr Chrysostomou describes the advanced receiver and refrigeration technologies used in SCUBA-2, giving wide-field images and sufficient sensitive to correct for variable atmospheric distortion. Dr Thompson explains what can be observed at these wavelengths, from molecular clouds made of very cold cosmic dust released by dying stars, which go on to form new stars, to debris discs, which go on to form planets. In particular, a neat quirk of nature means that SCUBA-2 can locate dusty galaxies both nearby and far away, because the redshift of the more distant galaxies brings their brighter emission into the submillimetre band. This allows astronomers to use the camera to investigate the roles of gas and dust in the formation of galaxies, stars and planets from the Milky Way back to the early Universe.
Interview with Prof. James Dunlop
Prof. James Dunlop, from the University of Edinburgh's Institute for Astronomy, talks to us about submillimetre galaxies and what information their study brings to our understanding of galaxy evolution. Using space telescopes such as Herschel, or larger ground-based instruments such as the brand-new SCUBA-2, we can observe these dust- and gas-filled monsters. As Prof. Dunlop explains, they are very active in star formation and are predecessors of the giant quiescent galaxies we observe in the local Universe.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during June 2012.
The constellation of Leo is setting in the west after sunset, with Mars below it. The brightest visible star is Arcturus, in the southern sky in Boötes. Corona Borealis is to its left. Continuing left, we reach Hercules, containing the Keystone asterism. Two thirds of the way up its right-hand side is the globular cluster M13, which is a fuzzy blob through binoculars but whose individual stars can be seen with a telescope. Rising in the east is the Summer Triangle of Vega in Lyra, Deneb in Cygnus and Altair in Aquila. Brocchi's Cluster, an asterism also know as the Coathanger, lies a third of the way from Altair to Vega. Ursa Major is overhead; within it, the second star in the handle of the Plough is a double named Mizar and Alcor. A telescope shows that Mizar is itself a double star. The right-hand stars of the Plough, Merak and Dubhe, point up towards Polaris, the North Star.
- Jupiter passed behind the Sun (superior conjunction) on the 13th of May and reappears this month in the pre-dawn sky. At the beginning of the month, it rises about 45 minutes before the Sun at magnitude -2; by month's end, it rises two hours before dawn. It is 34" in diameter and lies between the Hyades and Pleiades Clusters in Taurus. Saturn reached opposition (opposite the Sun in the sky) on the 15th of April. It is now in Virgo, about 5° about the first-magnitude star Spica and 20° above the horizon after sunset, towards the south. It's westward retrograde motion ends on the 26th of June, meaning that it does not move much relative to the stars during the month. Its magnitude drops from +0.5 to +0.7 as it moves away from us, while its angular size decreases from 18 to 17".
- Mercury can be seen for about an hour and a half after sunset in the latter half of the month, shining at magnitude 0. You may need binoculars to find it, but don't use them until the Sun has gone down.
- Mars drops in magnitude from +0.5 to +0.8 and in angular size from 8 to 6.6" over the month, and moves from Leo into Virgo on the 20th.
- Venus is at inferior conjunction (between the Earth and the Sun) on the 6th, but can just about be seen at the beginning of the month, 6° above the north-western horizon at sunset. By mid-June, it reappears half an hour before sunrise as a very thin crescent of magnitude -4.1, with just 2% of its disc illuminated.
- This month is a good one to observe noctilucent clouds, which are about 80 kilometres above the Earth's surface, sunlit from below the northern horizon. These bright, blue-white wisps are best seen after midnight, and may result from methane dissociating into water ice that crystallises around dust particles.
- Venus and Mercury are 12" apart on the 1st.
- Another supermoon occurs on the 3rd and 4th, when the Moon is full and close to perigee. Its area at this time is around 30% bigger than when it appears at its smallest.
- Mercury lies very close to a thin crescent Moon in the west just after sunset on the 21st. You may also see earthshine.
- Before dawn on the 29th, Venus will be in the Hyades Cluster and just below Jupiter, low in the west.
- A rare daytime highlight occurs on the 6th, when Venus passes directly across the face of the Sun for the last time this century. Only the last part of the transit will be visible in the northern hemisphere; in the UK this will be from sunrise at between 4:30 and 5am BST (British Summer Time, one hour ahead of Universal Time) to the end of the transit just before 6am. There has been a long fascination with transits of Venus, from prediction by Johannes Kepler, to the first recorded observation by Jeremiah Horrocks and William Crabtree in 1639, to timing measurements in 1761 and 1769 by the likes of Captain Cook, which allowed determination of the distance from the Earth to the Sun, as previously suggested by Edmond Halley. While you should never look directly at the Sun with the naked eye or unmodified magnifying equipment, you can use eclipse glasses or special telescope filters. Alternatively, you can follow Horrocks and Crabtree by projecting the transit using, for example, a pair of binoculars pointing into a shoebox.
John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during June 2012.
The winter solstice occurs on the 20th of June, marked by the dawn rising of Matariki (the Pleiades) and the star Puanga (Rigel). These are important transitions in Te Maramataka, the Māori annual calendar. The south-eastern sky is dominated by Scorpius and Sagittarius, the former containing the red star Antares, representing the Scorpion's heart. Antares is the sixteenth-brightest star in the night sky and has a faint companion, which can just about be seen against Antares' glare using a small telescope. Scorpius is a fishing hook to Māori and some Polynesian cultures, with Rehua (Antares) as the eye of the Hook. Many star clusters and nebulae can be observed around Scorpius, as the Milky Way passes through it. The globular clusters M4 and NGC 6144 are near Antares, a number of double stars appear along the Scorpion's body, and the open clusters NGC 6231, M7 and M6 (the Butterfly Cluster) are near its stinger. Binoculars or a telescope will reveal the individual stars in these clusters. Sagittarius, a Centaur and an archer in Babylonian mythology, also plays host to many nebulae and star clusters. The Lagoon Nebula, M8, has a compact core of stars surrounded by nebulosity containing dark rifts and globules where stars are forming. The Trifid Nebula, M20, is nebulous, but a medium-sized telescope reveals dark lanes that cut it into three. The brightest stars in Sagittarius form an asterism called the Teapot, near the top of which is the globular cluster M22, one of the brightest in the night sky. Other nearby star clusters are M23, M24, M25 and M55. An irregular dwarf galaxy known as Barnard's Galaxy, or NGC 6822, also resides in Sagittarius. The constellation is in the direction of the Galactic centre, so the Milky Way is at its most prominent in this region of the sky. The Māori called it Te Ika Roa, the Long Fish.
- Mars and Saturn appear in the evening sky.
- Jupiter is in the pre-dawn sky, where Venus joins it by the end of the month.
- A partial lunar eclipse occurs on the night of the 4th to 5th of June, with a maximum of 37% of the Moon's visible surface falling entirely under the Earth's shadow. The entire event is visible throughout New Zealand and most of Australia, with its maximum at 11:03pm NZST (New Zealand Standard Time, 12 hours ahead of Universal Time).
- The transit of Venus occurs during the day on the 6th, with the planet crossing the Sun over a period of around six hours. The sky will hopefully be clear, but the event will be streamed by a number of websites for anyone who cannot see it directly.
Odds and Ends
Venus is set to transit the Sun on the 5th-6th of June. If you live in the UK, you'll have to get up at sunrise on the 6th to see the last two hours. If you want to take part in a global citizen science project and follow in the footsteps of Captain Cook, check out Jodcast listener Grahame Bowland's attempt to measure the distance from the Earth to the Sun. You can take part by tweeting the time you observe Venus entering and leaving the disc of the Sun, and where in the world you are. The results you send will be used to calculate the astronomical unit live on the site as the event goes on. There is also a free smartphone app for a similar project. Whatever you do, make sure you observe the transit safely.
NASA has released an amazing video of the Sun using enhanced images from the Solar Dynamics Observatory. It highlights structure on the surface of the Sun, caused by convection and the magnetic field.
NASA released the results of its investigation of the Vesta asteroid by the Dawn spacecraft. Among other highlights, the orbiter discovered that Vesta resembles a planetoid in consisting of core, mantle and crust, and that it is responsible for 6% of Earth's meteorites. In August, Dawn will set off on a two-and-a-half-year journey to the dwarf planet Ceres, which is the largest of the asteroids.
The Dragon capsule, launched from the SpaceX Falcon 9 rocket, became the first commercial vehicle to dock with the International Space Station (ISS) on the 25th of May. The unmanned craft was captured by a robotic arm under the control of astronauts on the ISS, completing a milestone in the new era of commercial space flight. SpaceX intends future incarnations of the capsule to carry human crews.
Note: On the 31st of May, after recording, Dragon successfully splashed down in the Pacific Ocean and was retrieved.
A team from the Universities of Manchester and Cambridge will be hosting an exhibit all about ALMA at the Royal Society's 2012 Summer Science Exhibition in London from the 3rd to the 8th of July. The exhibit will be manned in part by some of the Jodcast team, so please come and say hello! As well as ALMA, there are teams representing the Herschel Space Observatory and cosmic ray experiments in the field of astronomy. There are also 18 other exhibits, covering all aspects of science from how animals see things to robots playing football!
|Interview:||Dr Patrick Sutton and Mark Purver|
|Interview:||Dr Antonio Chrysostomou, Dr Mark Thompson and Mark Purver|
|Interview:||Prof. James Dunlop and Melanie Gendre|
|Night sky:||Ian Morison and John Field|
|Presenters:||Adam Avison, Leo Huckvale and Mark Purver|
|Editors:||Mark Purver, Adam Avison, Claire Bretherton and Melanie Gendre|
|Segment Voice:||Cormac Purcell|
|Website:||Mark Purver and Stuart Lowe|
|Cover art:||The SpaceX Dragon capsule, held securely by the International Space Station's robotic arm, Canadarm2. CREDIT: NASA/ESA|
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