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April 2013: Forwards

April 2013

In the show this time, we talk to Dr Matt Auger about dark matter, Christina rounds up the latest news and we hear what we can see in the April night sky from Ian Morison and John Field.

The News

This month in the news: cosmological rulers, a distant ocean and an ancient wander.

Interview with Dr Matt Auger

Dr Matt Auger from the Institute of Astronomy at the University of Cambridge tells us about dark matter. He begins by telling us what dark matter is and goes on to tell us how he is investigating the properties of dark matter within galaxies and the methods of observing the effects of dark matter via graviational effects, including gravitational lensing. He also talks to us about the differences between various types of galaxies and why these differences exist.

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during April 2013.

The constellations of Orion, Taurus, Gemini and Auriga are setting in the west in the evening, with the planet Jupiter visible in Taurus. Cancer lies south of Gemini, with M44, the Beehive Cluster, at its centre. M67, another open star cluster, is to its lower left. Continuing around the sky, Leo the Lion is visible, its head and mane forming the asterism of the Sickle with the bright star Regulus at the bottom. A pair of binoculars or a small telescope reveals several galaxies below the Lion's belly. Virgo is to the south-east, and between the stars Denebola in Leo and Vindemiatrix in Virgo is the Realm of the Galaxies, a rich area of the sky for galaxy-hunters with medium-sized telescopes on a dark night. To the east, the orangey-yellow star Arcturus is in Boötes, beside the arclet of stars called Corona Borealis, the Northern Crown. Hercules is in the north-east, with four bright stars making a trapezium called the Keystone. Two thirds of the way up the right-hand side of the Keystone is the brightest globular cluster in the northern sky, M13, visible using binoculars. Vega, the brightest star in Lyra the Lyre, rises later in the evening. Ursa Major, the Great Bear, is above Leo and contains the recognisable asterism of the Plough, with Polaris due north in the constellation of Ursa Minor. Draco the Dragon winds its way around the Little Bear.

The Planets

Highlights

Southern Hemisphere

John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during April 2013.

Jupiter is low in the west after sunset, with a crescent Moon close by on the 14th and 15th. The second-magnitude star Alpha Librae is occulted by the Moon on the 26th, as seen from Australia and New Zealand. This begins at 22:35 NZST (New Zealand Standard Time, 12 hours ahead of Universal Time, UT) in Auckland, 22:41 in Wellington and 22:43 in Christchurch, ending before midnight. In Austrlia, the start time is 19:21 ACST (Australian Central Standard Time, 9.5 hours ahead of UT) for Alice Springs and 20:29 AEST (Australian Eastern Standard Time, 10 hours ahead of UT) for Hobart. The nearly-full Moon will make observation of the star difficult, and so a high-magnification telescope may be required.

Saturn rises in the east in the evening and is visible throughout the night, reaching opposition (furthest from the Sun in the sky) on the 28th. A small telescope reveals the planet's rings and its largest moon, Titan. The tilt of the rings varies as seen from Earth, and the brightness of the planet is currently invreasing as our view of the system opens out. The constellations of Orion and Gemini appear in the north-west after sunset, while Orion's two hunting Dogs, Canis Major and Canis Minor, follow him across the sky. The dwarf galaxies known as the Large and Small Magellanic Clouds appear as small patches of light near the bright star Achernar, and can be seen with the unaided eye under a dark sky. Binoculars or a small telescope show star clusters with the Large Magellanic Cloud, as well as the star-forming region of the Tarantula Nebula, which is illuminated by hot, young stars at its centre. This nebula is bright enough to spot with the naked eye on a moonless night. Near to the Small Magellanic Cloud is the globular cluster 47 Tucanae, also visible by eye and containing over a million stars, mostly very old. A telescope shows the density of stars decreasing from its centre. Omega Centauri is another globular cluster apparent to the naked eye, near to the Pointer Stars. Alpha Centauri, the brighter and lower of the two Pointer Stars, is the nearest star to Earth that can be seen without a visual aid. It is actually a binary star, 4.3 light-years away, with two stars similar in size and brightness to the Sun. A third star, Proxima Centauri, orbits the pair, while the dimmer of the main double stars hosts an Earth-sized planet. Besides Crux, the Southern Cross, is the Coalsack Nebula, a cloud of gas and dust which obscures the stars beyond. Many similar clouds can be seen along the Milky Way, and will eventually collapse under gravity to form new stars. A cluster of young, luminous stars called the Jewel Box is near to the second-brightest star in Crux. It appears as a fuzzy star to the unaided eye, while binoculars reveal individual stars within it. Two other cross-shaped asterisms can be found in the sky. The Diamond Cross sits near to Crux and contains the Theta Carinae Cluster at one of its points. With a central star surrounded by fainter stars, this cluster is sometimes called the Five of Diamonds of the Southern Pleiades. The False Cross is almost overhead, consisting of four similarly bright stars to one side of the Milky Way. A number of clusters and nebulae inhabit the area between the Diamond and False Crosses.

The planet Mercury is in the morning sky, shining at magnitude 0. On the 20th and 21st it is near Uranus, which can be seen in binoculars. Venus and Mars are too close to the Sun to be seen this month, with Venus reappearing as an evening object next month.

Odds and Ends

Astronomers have recently announced the discovery of a new type of supernova: Type IAx, which has also been dubbed "mini-supernova". Less energetic than their "normal-sized" cousins, Type Ia supernovae, these stellar explosions are interesting as they present a slightly different mechanism and are as yet poorly understood.

The Discovery Centre at Jodrell Bank Observatory has just finished installing its latest exhibit. A 5m diameter orrery! This mechanical representation of the orbits and positions of solar system bodies is moved by over 50 gears. The new exhibit is believed to be one of, if not the largest orrery in the world.

Astronaut Chris Hadfield commander of the international space station has made a series of videos about living in space. Highlights include cooking spinach in zero gravity and clipping your nails!!!

Show Credits

News:Stuart Harper and Christina Smith
Interview:Dr Matt Auger, Chris Wallis and Christina Smith
Night sky:Ian Morison and John Field
Presenters:Adam Avison, Libby Jones and Indy Leclercq
Editors:Adam Avison, Claire Bretherton, Mark Purver, Christina Smith and Chris Wallis
Segment Voice:Mike Peel
Website:Christina Smith and Stuart Lowe
Producer:Christina Smith
Cover art:A view of the trailing hemisphere of Europa in approximate true-colour. CREDIT: NASA

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