In the show this time, we talk to Prof. Ignas Snellen about finding exoplanets from the ground, Ian rounds up the latest news, and we find out what we can see in the May night sky from Ian Morison and Claire Bretherton.
In the news this month: Hubble turns 25, astronomers detect lunchtime and dark matter is mapped
The Hubble Space Telescope celebrated 25 years since its launch this month, drawing tributes and plaudits from across the astronomical community. The famous space telescope lifted off from the Kennedy Space Centre on the 25th of April 1990 and has since taken hundreds of thousands of beautiful and useful astronomical images which have revolutionised our picture of the Universe. It didn't always look good for Hubble. Even when it had made it to orbit, a notorious flaw in the construction of the primary mirror had it initially labelled a failure. Due to an incorrectly assembled piece of testing equipment, the mirror had been ground incredibly precisely -- but to the wrong shape. This caused a spherical abberation in images sent back by Hubble, and whilst the images were still superior to those of a typical ground-based telescope, they were nowhere near the sharpness which had been designed and expected. Fortunately, a series of maintainence missions had always been planned for Hubble and the first of these was able to install corrective "spectacles" in 1993, with spectacular results. Since then, the telescope has operated nearly continuosly, with four further service missions refreshing its cameras, spectographs and computers. The images produced have been spectacular, as summarised in the many anniversary lists available online, but Hubble also released a special image of the Westerlund 2 star cluster in the Carina constellation, showcasing the high resolution, wide-field images which simply would not be possible to achieve when looking through the Earth's unstable atmosphere from the ground.
Hubble has done excellent science both inside and outside our own galaxy, including on projects viewing the impact of the Shoemaker-Levy 9 comet on Jupiter, views of the birthplaces of stars and planets within our own galaxies, precision determinations of the rate of expansion of the Universe and the Deep Field studies -- staring at an apparently empty patch of the sky for a long period in order to gather the faint light from some of the earliest galaxies in the Universe. These Deep Fields are particularly humbling, revealing tiny patches of sky to contain thousands of galaxies billions of light years away, each hosting innumerable of stars and planets. Even after 25 years, Hubble is still capable of groundbreaking science, but is nearing the end of its time in space. The cost of its replacement -- the James Webb Space Telescppe (or JWST), which will haveover five times the collecting area -- is such that it has become difficult to justify service missions to Hubble, meaning a hard limit on its lifetime is set by either equipment failureor its gradual orbital decay, with best estimates as to the end of the mission between 2020 and 2030. For now though, Hubble observing time remains one of the most prized goals of many astronomers.
Also this month, astronomers showed that a mysterious signal detected by radio telescopes actually has a banal origin: as emission from a local microwave oven. The signals, known as "Perytons" had been detected at telescopes including the Parkes radio dish in New South Wales, Australia and were previously of unknown origin. However, work from Emily Petroff and collaborators was made available on the arXiv service this month has shown they actually originate from impatient astronomers in the Parkes staff room, opening the door of a microwave oven before the timer had expired, releasing the burst of radio waves. Since their description in 2011, Perytons have been detected in archival data and been an annoying foreground in the searches for another mysterious radio signal: Fast Radio Bursts (FRBs or "furbies"). Perytons are regarded as less interesting by astronomers as they were known to have some kind of terrestrial origin, unlike furbies which are expected to originate outside of our galaxy. However the two types of signal have a similar frequency signature, leaving lingering doubts in the minds of some that they could both be man-made. Perytons had still had a number of potentially exotic explanations, including as artifacts from ball lightning, metoer trails and large magnetic fields. In the end the crucial clue about their true nature came from their distribution in time -- that is, their appearance in the Parkes data was clustered strongly around lunchtimeat the telescope. Following a hunch, Petroff and the paper's other authors were able to reproduce Peryton signals at will using two microwave ovens installed in staff kitchens at the observatory. Their paper contains surely some of the most incongruous discussion in anastronomical publication; on the particulars of components and operations of two 27 year old microwaveovens, the use of a cermaic mug of water as a test load and the detection in data from 1998 of a cluster of Perytons inferred to be from a hungry astronomer defrosting a meal with a small amount of foil caught in the oven door. The paper has generated much amusement, but is invaluable in showing a definite and distinct origin for the Perytons, removing any lingering doubts that they were related to the more interesting (due to their apparent extraglactic origin) FRBs. The microwave ovens are still in working order and have not been retired, but new guidelines for their use have been strictly implemented.
And finally, the Dark Energy Survey (DES) collaboration released their first map of the dark matter within our Universe this month. The team used data from their Dark Energy Camera (DECam) at the Victor M. Blanco telescope in Chile to measure the shapes of thousands of distant galaxies. They then used the fact that the gravity of objects between us observers and those galaxies distorts by a tiny amount their apparent shapes in an effect known as weak gravitational lensing. By looking at the shapes of thousands of galaxies in a 139 square degree patch of sky, the international team were able to see where distortions were greatest, showing them where the mass was. This total mass is expected to be dominated by dark matter, which cannot be directly seen by other means. The resulting map of dark matter is one of the largest so far made and proves that the DES team are capable of this very difficult science. In the coming years they hope to expand their region to a full 5000 square degrees of sky, enabling then to measure the growth of structures in the dark matter over the history of the Universe and inferring the effect which the even more mysterious Dark Energy has had on that growth.
Interview with Prof. Ignas Snellen
Prof. Ignas Snellen from Leiden University is an exoplanet researcher. He explains the different techniques used to detect exoplanets, talks about the different types of exoplanets discovered so far, and delves into the prospects of detecting exoplanets using ground-based telescopes as well as space missions.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during May 2015.
The winter constellations of Orion, Taurus and Gemini are setting in the west after sunset, with Auriga close behind. Leo is higher in the sky to their left, and further over is the bright star Arcturus in Boötes. Between them, in an otherwise fairly blank part of the sky, the Realm of the Galaxies offers 18 Messier objects to telescopic observers. The Summer Triangle rises in the east later in the evening, consisting of the bright stars Vega in Lyra, Deneb in Cygnus and Altair in Aquila. The constellation of Hercules is between Arcturus and Vega, and its four brightest stars make a trapezium called the Keystone. Two-thirds of the way up the Keystone's right-hand side, binoculars can locate the globular cluster M13. The asterism of the Plough is overhead, its hindmost stars, Merak and Dubhe, pointing towards Polaris in the north. Below Polaris is the W-shaped constellation of Cassiopeia.
- Jupiter is in the south-south-west after dark. Receding from us, its brightness declines from magnitude -2.1 to -1.9 during the month, while its angular diameter decreases from 38 to 35". It moves eastwards from Cancer towards Leo, and a telescope shows its equatorial bands, Great Red Spot and Galilean moons. From 22:00 BST (British Summer Time, 1 hour ahead of Universal Time) on the 20th, observers can see the shadow of the moon Ganymede passing across Jupiter, followed by the moons Callisto and Io themselves.
- Saturn reaches opposition this month, when it is opposite the Sun in the sky and due south at around 01:00 BST.
- Mercury passed superior conjunction (behind the Sun in the sky) on the 10th of April, and can be seen low in the west after sunset in early May, a few degrees from the Pleiades Cluster in Taurus. It is best seen on the 7th, 22° from the Sun in the sky at eastern elongation. Its brightness falls from magnitude -0.4 at the beginning of the month to +3.0 in the middle, when it becomes lost in the Sun's glare. At the same time, its angular size grows from 6.8 to 11".
- Mars may be just visible on the 1st, 9° below the Pleiades Cluster and shining at magnitude +1.4, but is lost in the twilight after this. With an angular size of 3.8", it is too small for surface details to be seen.
- Venus shines brilliantly in the west after sunset, climbing from Taurus into Gemini and passing the star Epsilon Geminorum on the 16th. On the way to its greatest separation from the Sun in the sky on the 6th of June, it brightens from magnitude -4.2 to -4.4 and grows from 16 to 22" during May, while its illuminated fraction drops from 67 to 53%.
- Saturn is well placed for observation this month, as it reaches opposition on the 23rd and is therefore visible for most of the night. The rings are inclined at 24° to the line of sight, almost as visible as they can ever be. Saturn brightens to magnitude 0 during May, its brightest for 8 years, with the planet spanning 18.5" and the rings 42". Around the time of opposition, the lack of shadow on the ring system makes them appear brighter than usual, a phenomenon known as the Seeliger Effect. Saturn is moving retrograde (westwards) away from the double star Beta Scorpii and towards the constellation of Libra, which it reaches on the 12th. Unfortunately, it cannot currently be seen higher than 18° above the horizon from the UK, making atmospheric scintillation a problem for viewers.
- Mercury can be seen between the Pleiades and Hyades Clusters shortly after sunset on the 2nd.
- The Eta Aquariid meteor shower peaks before dawn on the 6th. The radiant, in Aquarius, is low in the south-eastern sky, but some meteors may be spotted around 90 minutes after sunset. A waning gibbous Moon in the west may hinder the view slightly.
- Venus and a crescent Moon are close together about an hour after sunset on the 21st and 22nd. Venus is below the stars Castor and Pollux in Gemini, with the Moon to its lower left on the 21st and to its left on the 22nd.
- Jupiter appears near the crescent Moon around 22:00 BST on the 23rd and 24th, close to the Mane of Leo the Lion. The Moon is below Jupiter on the 23rd and to its left on the 24th.
- Around the 23rd, Saturn is just above the fan of stars that marks the head of Scorpius. It is in the south-east at around 23:00 BST and rises higher over the following two hours.
- Comet Lovejoy is still visible as a faint, fuzzy ball this month, and can be found using binoculars or a small telescope when it passes within 1° of the star Polaris on the 28th.
Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during May 2015.
Three bright planets are visible in the early evening. Venus appears low in the north-west as the Sun sets, outshining everything except the Sun and Moon as its atmosphere reflects almost 70% of the sunlight that falls on it. Jupiter appears soon after Venus, just to the left of the head of Leo the Lion in the north. It sets around midnight NZST (New Zealand Standard Time, 12 hours ahead of Universal Time) at the beginning of the month and 22:00 at the end, and is near the Moon in the sky on the 24th. Saturn rises a little later in the east, officially in Libra but close to the Claw of Scorpius and to the left of the star Antares. It is at its brightest and closest to us around the time of opposition on the 23rd, and appears high in the north at midnight. Its rings are inclined favourably for viewing, and the Moon passes within 2° of it on the 6th.
On the same night, the Earth's passage through debris from Comet Halley causes the peak of the Eta Aquariid meteor shower, so named because the meteors appear to radiate from a point (the radiant) near the fourth-magnitude star Eta Aquarii in Aquarius. The radiant rises around 02:00 NZST in New Zealand, and up to a meteor a minute may be spotted streaking across the sky - although the Moon will obscure the fainter ones. The more minor Alpha Scorpiid meteor shower peaks on the 13th, its radiant near to Antares and Saturn. Although visible throughout the night and largely unhindered by the thin crescent Moon, it provides no more than 5 meteors per hour.
To the lower-left of Saturn, in the constellation of Serpens, is the globular cluster M5, also called NGC 5904. At magnitude +5.7, binoculars can be used to view it, while a small telescope picks out some of its hundreds of thousands of stars. It is home to over one hundred variable stars, the brightest of which is called Variable 42 and changes from magnitude +10.6 to +12.1 and back every 26.5 days. M5 is around two-thirds of the way from the red star Antares to the orange star Arcturus in Boötes, which rises in the north-east after dark. Above Arcturus is the bright blue star Spica, in Virgo, which is actually a double.
On the opposite side of the sky, Comet C/2015 G2 (MASTER) is expected to reach a peak brightness of magnitude +5.4 on the 14th, making it easily visible in binoculars. The comet begins May in the constellation of Sculptor, resides in Fornax from the 9th to the 14th, moves through Eridanus, Lepus and Canis Major and ends the month in Monoceros. It is visible above the south-western horizon after dusk on the 14th, setting just after 21:00 NZST.
Odds and Ends
Interested in geography and astronomy? Here is a way to combine the two! NASA Astronaut Scott Kelly was recently launched into space to spend one year on the International Space Station and while he is there he will be taking a series of photographs of Earth. Each Wednesday a new photo will be posted on his Twitter feed and if you are the first to identify where on Earth he has taken a picture of then you will win a signed copy of the photograph. To join in follow Scott Kelly on Twitter @StationCDRKelly . For full terms and conditions click here.
The Atacama Large Millimeter/Submillimeter Array (ALMA) issued a press release in April announcing the results from their first experiments with placing the antella on long baselines. This means that the antennas were spread out over distances as long as 15 km, which allows astronomers to produce sharper images with ALMA than what can be done with a more compact configuration. The multi-ringed structure in the protoplanetary disc HL Tau was previously discussed in a November 2014 press release; astronomers think that these rings could be related to the growth of dust grains in the disc, which would be the first step in planet formation. One of the new results is an image of the gravitational lens SDP.81, which looks like a nearly-perfect ring. The image contains enough detail that astronomers can use models to map structures within the gravitationally-lensed galaxy. The press release also contains multiple images of the asteroid Juno, and it is possible to see the asteroid rotating in the images. Additional details as well as images are available from the press release.
The Spitzer Space Telescope collaboration with the Polish Optical Gravitational Lensing Experiment (OGLE) have discovered their first exoplanet, which is one of the most distant discovered. The experiment uses a method of detecting exoplanets called microlensing, which is a phenomenon that occurs when a star passes in front of another and the gravitational field acts as a lens to magnify the more distant star. An exoplanet has a bit of extra gravity and causes a blip in the light curve of the event, which is related to the size and orbit of the planet. The experiment is unique in that it takes advantage of the different vantage points between the ground-based Polish telescope and Spitzer, which is in solar orbit and around 207 million km from Earth. This creates a time delay between observed events, from which the distance to the exosolar system can be determined. It is hoped this will allow astronomers to understand how planets are distributed around stars in the Milky Way.
|Interview:||Prof. Ignas Snellen and Indy Leclercq|
|Night sky:||Ian Morison and Claire Bretherton|
|Presenters:||George Bendo, Josie Peters and Hannah Stacey|
|Editors:||Adam Avison, Indy Leclercq and Mark Purver|
|Segment Voice:||Iain McDonald|
|Website:||Indy Leclercq and Stuart Lowe|
|Website:||Indy Leclercq and Stuart Lowe|
|Cover art:||An image of the Westerlund 2 region taken by Hubble, released for the 25th anniversary celebrations. CREDIT: NASA/ESA/Hubble Heritage team,A.Nota and the Westerlund 2 Science team|