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September 2011: Diamond

September 2011

In the show this time, we talk to Dr Martin Bureau about galaxies and we find out about an exciting new discovery in the pulsar world. As always, Megan rounds up the latest news and we hear what we can see in the September night sky from Ian Morison and John Field.

The News

In the news this month:

Interview with Dr Martin Bureau

Dr Martin Bureau (Oxford University) studies the molecular gas in local early-type galaxies. In this interview, he tells us what an early-type galaxy is, how studying the molecular gas in these galaxies might change our understanding of galaxies and what telescopes he uses to observe them.

Interview with Dr Ben Stappers and Lina Levin

The discovery of a 'diamond planet' orbiting a pulsar caused a stir in the media at the end of last month. Here we find out the real story from two of the researchers involved in the discovery. Dr Ben Stappers of the University of Manchester's Jodrell Bank Centre for Astrophysics tells us about the likely history of the planet, accreted and ablated from a white dwarf companion into a dense carbon-oxygen planet, while Lina Levin of the Swinburne University of Technology in Melbourne, Australia, discusses the international pulsar survey which found it.

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during September 2011.

The Summer Triangle of the stars Deneb, Vega and Altair, in the constellations of Cygnus, Lyra and Aquila, is visible in the south after dark. Just to the left of Vega, which is in the top-right of the triangle, binoculars show a double star called Epsilon Lyrae, with two stars just about distinguishable to the naked eye. A small telescope reveals that each of these stars is itself a double, and the system is known as the 'Double Double'. The stars in each pair have an orbital period of several hundred years, while the pairs orbit one another every million years or so. Looking from Vega down to Altair, your line of sight crosses the dark Cygnus Rift in the Milky Way, where interstellar dust obscures the centre of the Galaxy. Brocchi's Cluster, with its asterism of the Coathanger, resides here. Comet Garradd passes to the right of it in the sky on the 2nd and 3rd of the month, moving westward towards Hercules. Pegasus, the Winged Horse, is to the left of Cygnus. Looking to the right of the Square of Pegasus, the Sun-like star 51 Pegasi is visible. It is home to the first extrasolar planet found to be orbiting a main-sequence star: a planet of half the mass of Jupiter but orbiting every 4.2 days, making it very hot and surprisingly close to its star. The planet-hunting spacecraft Kepler observes the stars between Cygnus and Lyra, and has found planets only slightly larger than Earth. After a year or two of observations, it will be able to detect planets with similar orbits to Earth as well as similar masses, and will give an indication of how common habitable planets might be. The Milky Way's neighbour, the Andromeda Galaxy, appears not far from the top-left of the Square of Pegasus. It was here that Edwin Hubble observed a Cepheid variable star in 1924, whose known relationship between brightness and period of brightness variation told him that Andromeda was outside our own Galaxy.

The Planets


Southern Hemisphere

John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during September 2011.

The Spring Equinox occurs on the 23rd of the month, after which the days become longer than the nights. The constellations of Scorpius and Sagittarius are in the west in the evening sky, followed by Capricornus, Aquarius and Pisces, while Orion rises in the small hours. Capricornus, depicted with head of a goat and the tail of a fish, appears as an elongated triangle with its tip facing away from Sagittarius. 2500 years ago, the goat's head was below the Sun at the time of the summer solstice, when the Sun was directly overhead for observers on the Tropic of Capricorn - the latitude line at 23.5° south on the Earth's surface. Precession of the Earth's rotational axis means that Sagittarius is now in the place of Capricornus for observers on this line at the summer solstice. In Capricorn, Alpha Capricorni is a double with stars at magnitudes +3.6 and +4.2, and the two can be distinguished with the naked eye. It is called Algedi in Arabic, meaning 'billy goat'. Beta Capricorni is another double, with a yellow star of magnitude +3.1 and a blue-white companion of magnitude +6, and is resolvable in binoculars. The brightest star in the constellation is Delta Capricorni, in the tail, at magnitude +2.9, which is about 40 light-years away and actually consists of four stars. Aquarius, symbolically pouring water onto the Earth, contains several deep-sky objects. M2 is a globular cluster that can be found with binoculars, near the 3rd-magnitude star Beta Aquarii. The cluster is just visible to the naked eye at magnitude +6.3, but only in a dark sky. A telescope can pick out individual stars, which, at around 13 billion years old, are among the most ancient in our Galaxy. South-west of Delta Aquarii lies NGC 7293 - the Helix Nebula - the largest planetary nebula in our sky and the closest to us at 700 light-years' distance. It covers half the angular size of the full Moon, corresponding to a diameter of 2.5 light-years. NGC 7009, the Saturn Nebula, is another planetary nebula, located near Eta Aquarii. The small constellation of Delphinus, the Dolphin, is below Aquarius. Its nose is Gamma Delphini, a double of golden-yellow stars at magnitudes +4.3 and +5.2. Crux, the Southern Cross, is on its side in the south-west after sunset. Though the smallest of the 88 constellations, it is one of the most recognisable in the southern hemisphere. An imaginary line can be drawn from Gamma Crucis at the top, through Alpha Crucis at the bottom, and on towards the bright star Achernar, halfway along which the south celestial pole is located. Continuing the line to the ground shows the direction of south. To Māori, the Cross is Te Punga - the Anchor - while in Tonga it is Toloa - the Duck. An image of the Cross at Machu Picchu labelled it as Chakana - the Stair - in the Inca language. Alpha and Beta Centauri are near to the Cross. Alpha Centauri is the third-brightest star in our sky and the nearest to Earth at a distance of 4.3 light-years. It is a double that can be split using a small telescope, while a larger telescope reveals a third star apparently in the system: the red dwarf Proxima Centauri, currently the closest actual star to the Sun. It may be orbiting the Alpha and Beta Centauri system, or they could both be part of a larger cluster. The activity of our own Sun is now increasing, with more features such as sunspots resulting from the varying magnetic field. This activity follows an 11-year cycle, but emergence from its minimum over the last two years has been slower than expected due to longer-term variation.

The Planets

Odds and Ends

On August 24, a Russian Progress spacecraft crashed soon after launch.

NASA is aiming to launch its next mission to the Moon on September 8. The Gravity Recovery and Interior Laboratory (GRAIL) will place two spacecraft orbiting around the Moon.

The Astronomy Picture of the Day on August 26 featured the new supernova spotted in M101.

The astronomers at the Royal Observatory Greenwich will be live-tweeting the results of the Astronomy Photographer of the Year 2011 competition on September 8 using the hashtag #astrophoto11.

The programme for the 2011 Manchester Science Festival is now online, and includes Rocket Week at the Jodrell Bank Discovery Centre.

Show Credits

News:Megan Argo
Interview:Dr Martin Bureau, Jen Gupta and Libby Jones
Interview:Dr Ben Stappers, Lina Levin and Mark Purver
Night sky:Ian Morison and John Field
Presenters:Jen Gupta, Evan Keane and Mark Purver
Editors:Jen Gupta, Megan Argo, Claire Bretherton, Melanie Gendre and Mark Purver
Segment Voice:Liz Guzman
Website:Jen Gupta and Stuart Lowe
Producer:Jen Gupta
Cover art:Optical image of the elliptical galaxy NGC 4636 taken from the Sloan Digital Sky Survey CREDIT:: SDSS

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