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May 2015: Sleuths

May 2015

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.

The News

In the news this month: Hubble turns 25, astronomers detect lunchtime and dark matter is mapped

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

Northern Hemisphere

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.

The Planets


Southern Hemisphere

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.

Show Credits

News:Ian Harrison
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

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