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December 2012: Argo

December 2012

In the show this time, Dr Phil Marshall talks to Libby about how and why he weighs galaxies, Ian Morison and John Field bring us the December night sky and Megan gives her last-ever round-up of the astronomy news.

The News

Interview with Dr Phil Marshall

Dr Philip Marshall is a Royal Society Research Fellow at the University of Oxford. In this interview, Phil tells us how he goes about weighing galaxies using gravitational lensing and how this relates to the fraction of their mass that is composed of dark matter. He also describes how to measure the expansion rate of the Universe.

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during December 2012.

The constellations of Cygnus, Lyra and Aquila are in the west after sunset. Taurus, Orion, Gemini and Canis Major rise in the east as the evening progresses. To the south is the Square of Pegasus, containing around 8 visible stars if your eyes are sensitive enough. You can star-hop from the Square to the Andromeda Galaxy and may also see M33, the Triangulum Galaxy. The Pleiades and Hyades star clusters are in Taurus, with the planet Jupiter between them. The bright star Aldebaran appears to be within Hyades, but is actually nearer to us. Below Taurus is Orion, with the Orion Nebula visible as a fuzzy glow beneath the Hunter's Belt. Below the bright star Sirius, in Canis Major, is the open cluster M41. Most of its stars are young and blue, but there is a red giant at its centre.

The Planets


Southern Hemisphere

John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during December 2012.

The northern sky is dominated by the consellations of Orion, Taurus, Canis Major and Canis Minor. The summer part of the Milky Way passes through them and stretches along the southern horizon, with bright regions of combined starlight and dark patches where clouds of interstellar dust and gas obscure the stars beyond. Orion's Belt is in the north, consisting of three giant blue stars. Alnitak, the easternmost of the three, is a double star system that can just about be split with a small telescope. NGC 2024, the Flame Nebula, is illuminated by Alnitak, while IC 434, which includes the dark Horsehead Nebula, is also nearby - Alnitak makes both hard to see but they show up well in long-exposure photographs. The Sword of Orion is made up of three stars aligned above the Belt, the middle of which is actually the Orion Nebula. The nebula is illuminated by a star at its centre, and forms part of a much larger cloud of mainly dark gas. Binoculars or a small telescope reveal detail in the nebula, while a photograph brings out its colours. The larger and brighter Carina Nebula sits towards the south, between the False and Southern Crosses. Betelgeuse, a red giant star marking one of the Hunter's shoulders, is below Orion's Belt. Its brightness varies between magnitudes +0.2 and +1.2 with a period of about six years. Rigel, marking one of Orion's feet, is a blue giant star above the Belt, and has a companion that is visible in a medium-sized telescope.

The V-shape of the head of Taurus is to the left of Orion in the evening sky. The planet Jupiter currently sits about halfway between the horns and the head of the Bull and is in its brightest apparition of the year. The Moon moves through Taurus and past the Pleiades star cluster just before Christmas Day, before swinging by Jupiter and the star Aldebaran. Uranus and Neptune are visible in Pisces and Aquarius, respectively, in the evening sky. Crux is low in the south-east with a dark cloud called the Coalsack Nebula beside it. Though optically dim, the nebula has bright infra-red hotspots where stars are forming as gas collapses under gravity, giving off light that is absorbed and re-emitted by the cloud. Eventually the stellar winds from the infant stars will break up the nebula, leaving a star cluster similar to the Jewel Box and Pleiades. Another visible nebula is the Large Magellanic Cloud, which is in fact a satellite galaxy of the Milky Way. Binoculars or a small telescope show that it possesses star clusters and nebulae of its own. The Small Magellanic Cloud, another satellite galaxy, and the bright, round globular cluster 47 Tucanae, are nearby. NGC 362 is another globular cluster than can be found in the vicinity using a small telescope.


Odds and Ends

Astronomers have used an occultation of a star by the dwarf planet Makemake to shine a light on this distant Kuiper Belt object. They used the changes in the starlight to deduce that Makemake has no measurable atmosphere and is a body of ice and rock around 1.7 times denser than water.

A plan for a Mars colony has been devised by SpaceX CEO Elon Musk. The colony would eventually support up to 80,000 people, who would pay some $500,000 for the trip. In this vision for the future, the initial settlement and infrastructure would be established in the coming decades by a small 10-person crew.

Show Credits

News:Megan Argo
Interview:Dr Phil Marshall and Libby Jones
Night sky:Ian Morison and John Field
Presenters:Megan Argo, Libby Jones and Mark Purver
Editors:Dan Thornton, Megan Argo, David Ault, Claire Bretherton and Mark Purver
Intro/outro script:David Ault
Narrator:Christina Smith
Meg:Megan Argo
Old Man:David Ault
Meg's Mum:Mark Purver
Giantess:Libby Jones
Telescope:Liz Guzman
Goose:Cat McGuire
Harp:Stuart Harper
Giant:Iain McDonald
Segment Voice:Cormac Purcell
Website:Mark Purver and Stuart Lowe
Producer:Libby Jones
Cover art:A photograph taken by the Hubble Space Telescope's Wide Field Camera 3, showing the light from a distant blue galaxy gravitationally lensed into an Einstein ring by the mass of an intervening red galaxy, with other galaxies in the background and two nearby stars in the foreground. CREDIT: ESA/Hubble & NASA

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