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November 2013: Trigger

November 2013

In the show this time, we talk to Prof Clive Tadhunter about AGN and their trigger mechanisms, Stuart rounds up the latest news and we find out what we can see in the November night sky from Ian Morison and John Field.

The News

This month in the news, how a supernova becomes a hypernova.

Interview with Clive Tadhunter

Prof. Clive Tadhunter from The University of Sheffield talks to us about Active Galactic Nuclei (AGN) and how they are triggered.He starts off by explaining what, exactly, AGN are - and then goes on to explain how we think they come into existence. Current theories believe that galaxy mergers are what trigger the inflow of gas towards a central black hole necessary for the generation of huge amounts of energy and light via accretion, although Prof. Tadhunter explains that the picture isn't as straightforward as that.

The Night Sky

Northern Hemisphere

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

The Summer Triangle is visible, as usual. It is in the west after sunset, while Pegasus makes its way over to the south-west during the evening. The globular cluster M15 is close to the star Enif, at the front of the head of the upside-down Winged Horse. Alpheratz, one of the upper stars in the Square of Pegasus, can be used as a starting point to locate M31 and M33, the Andromeda and Triangulum Galaxies. Taurus rises in the south-east in the evening, containing the Hyades and Pleiades Clusters. Cassiopeia is high overhead, and you can follow the Milky Way down from there to Auriga, with its bright yellow star Capella, and then Gemini, with the stars Castor and Pollux forming the heads of the Twins.

The Planets


Southern Hemisphere

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

After sunset, the winter constellations are seen sliding towards the western horizon as the summer stars rise in the east. Scorpius is one of those setting, and its tail marks one of four pillars in Māori star lore. Ranginui, the Sky Father, rests on these pillars, and the other three mark the rising points of Te Rā (the Sun) at the solstices and equinoctes, as seen from New Zealand: Takurua (Sirius), the brightest star in the night sky, rises in the east-south-east, like the Sun at the summer solstice; Matariki (the Pleiades Cluster) rises in the east-north-east, like the Sun at the winter solstice; Tautoru (Orion's Belt) rises due east, like the Sun at the equinoctes. Te Punga, the Southern Cross, skirts the southern horizon as it reaches its lowest point in the night sky. It is sometimes seen as the anchor of the Waka (canoe) of Tamarereti, who sailed across the sky placing Ngā Whetū (the stars) across the body of Ranginui. The Diamond Cross and False Cross asterisms can also be seen low in the south, and the bottom star of the Diamond appears slightly fuzzy due to its being surrounded by a cluster of dimmer stars. Between these crosses lies the Carina Nebula, in which binoculars or a telescope can pick out swirls of luminosity and star clusters. Eta Carinae, one of the most massive stars known, is beside the nebula. The star Achernar is high above the Southern Cross, and between the two are the Magellanic Clouds, dwarf galaxies near to the Milky Way. The bright globular cluster 47 Tucanae is nearby in the sky, in the constellation of Tucana, the Toucan. Alpha Tucanae is a yellow giant star of magnitude +2.8, while Beta Tucanae is actually a group of six stars which seem to be loosely bound together by gravity.

The Leonid meteor shower occurs this month, and is best observed about three hours before sunrise from the 15th to the 17th. It originates from dust shed by Comet Tempel-Tuttle as it comes close to the Earth every 33 years. Its shooting stars appear to come from Leo the Lion, a constellation marked by a sickle shape that represents the chest and head.This year's shower coincides with a full Moon, hampering viewing.

The constellations of Orion and Taurus are visible from all over the Earth, because they straddle the celestial equator. Rigel, Orion's brightest star, is one of the Hunter's feet, but is at the top as seen from the southern hemisphere. It has a companion star, Rigel B, which is usually lost in the glare of Rigel even though it has a magnitude of +6.7 and would otherwise be visible in binoculars. Rigel is called Puanga by Māori, and its dawn rising over the lower North Island of New Zealand heralds the new year. Betelgeuse, one of Orion's shoulders, is a bright red giant star which is cooler than the Sun because it is swollen by the fusion of helium at its core as it nears the end of its life. Taurus is next to Orion, and is currently on the opposite side of the sky to the Sun, which is now in the lesser known constellation of Ophiuchus.

Comet ISON will hopefully brighten to naked-eye visibility this month. It swings past the Sun on the 28th and 29th of November, passing just over one million kilometres from it. It may be best seen after perihelion, when it crosses into the northern hemisphere sky.

Odds and Ends

A galaxy more distant than any other yet observed has been discovered. Z8_GND_5296 formed within 700 million years of the beginning of the universe, and is about 13.1 billion light-years away. Discoveries like this are exciting because they give astronomers the opportunity to study galaxies as they were in the early universe. Z8_GND-5296 has an unusually high rate of star formation, a characteristic it shares with the previous record-holder for the most distant galaxy. An article on the new discovery was published on on October 23rd.

Space tourism is set to get ever so slightly more accessible in the next few years if a new company, World View Enterprises , succeeds in its plan to offer balloon rides to the edge of space, 30 km (19 miles) up into the atmosphere. At this altitude, the blackness of space and the curvature of the Earth are visible, even if the 'official' boundary of the atmosphere is 100 km (62 miles) up.

NASA Scientist Dr. Harold White is working on creating space warp bubbles,which would potentially allow faster than light space travel. The idea was first proposed by Miguel Alcubierre in 1994 and is similar to the warp drive technology used on board the Star Ship Enterprise! The Alcubierre drive required the existence of exotic matter and large amounts of energy to warp space, but Dr. White and his colleagues are working on methods which would reduce these energy requirements. They aim to test their technology by warping the space around photons.

Show Credits

News:Stuart Harper
Interview:Indy Leclercq and Clive Tadhunter
Night sky:Ian Morison and John Field
Presenters:Cat McGuire, Fiona Healy and Indy Leclercq
Editors:Indy Leclercq, Sally Cooper, Francesca Lucini and Mark Purver
Segment Voice:Mike Peel
Website:Indy Leclercq and Stuart Lowe
Producer:Indy Leclercq
Cover art:Hubble space telescope image of the most distant galaxy ever seen, Z8_GND_5296

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