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August 2011: Witless

August 2011

In the show this time, we talk to Dr Philipp Podsiadlowski about all sorts of different supernovae. As always, Megan rounds up the latest news and we hear what we can see in the August night sky from Ian Morison and John Field.

The News

In the news this month:

Interview with Dr Philipp Podsiadlowski

Dr Philipp Podsiadlowski of Oxford University studies supernova explosions. Here he talks about different types of supernova, using modelling to try to determine the history of an object from its supernova remnant, and why it is often difficult to connect an observed supernova to an expected theoretical type. Supernovae can happen in a range of different scenarios, from the collapse of an aged massive star to the accretion of material onto a white dwarf, and each involves different physical mechanisms. As he discusses in this interview, the famous Supernova 1987A involved a surprisingly young-looking (i.e. blue) star, which may have resulted from the merger of two stars, one of which was near the end of its life, some 20,000 years earlier.

The Night Sky

Northern Hemisphere

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

On a clear night, you can't help but see the constellations Cygnus the swan, Lyra the lyre and Aquila the eagle, with their bright stars Deneb, Vega and Altair making up the summer triangle. Just below Cygnus is Delphinus the dolphin, below Delphinus is the constellation Equuleus and then there are two constellations below: Aquarius and Capricornus. Over to the left of Delphinus is Pegasus (upside down as we see it in the northern hemisphere) with four stars making up the square of Pegasus. The top left-hand star of the square of Pegasus is Alpheratz (or alpha Andromedae) and is also part of the Andromeda constellation, which contains the Andromeda galaxy, M31.

There are two ways to find M31. Starting at Alpheratz, move one bright star to the left, then turn a bit upwards to a second bright star. Go the same distance again and then turn sharp right to one star not far away. Go the same distance again and you should see M31 as a fuzzy object, close to another fainter star. M31 is easily visible with binoculars, or possibly with the unaided eye on a dark, transparent night with no Moon. Continuing upwards from M31 is the constellation Cassiopeia, the 3 rightmost stars form a V-shape that points towards M31. Taking the top left star of that V and going to the next star in Cassiopeia points towards Perseus. Scan along from Cassiopeia down into Perseus with binoculars and you'll see a fuzzy glow which is a pair of open clusters called the Perseus double cluster.

The Planets


Southern Hemisphere

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

This month we look at the region of sky stretching northwards from the constellation of Sagittarius to the star Deneb, low above the horizon. The Milky Way is at its thickest and brightest in Sagittarius, thinning along the Cygnus Arm towards Deneb. A dark rift of interstellar gas and dust runs through it, blocking the light of the stars beyond. The celestial birds, Aquila the Eagle and Cygnus the Swan, fly through this part of the night sky. The four brightest stars in Cygnus form the Northern Cross; Deneb is the brightest and marks the tail, while Albireo is the head. Deneb is the 19th-brightest night-time star and is around 1500 light-years away. With binoculars or a telescope, Albireo can be seen to be a double star consisting of a blue star and a yellow companion, the latter itself a double. 31 Cygni is another double, with orange and turquoise components, but appears very low in the New Zealand sky. 61 Cygni was the first star whose distance was measured by parallax, a feat accomplished by Friedrich Wilhelm Bessel in 1838. It is nearby at 11.4 light-years' distance, and is another double. Aquila is marked by a line of three stars, the brightest of which, Altair (meaning 'flying eagle' in Arabic), is 17 light-years from us. Aquila contains a number of observable star clusters such as NGC 6709 and NGC 6755, and planetary nebulae such as NGC 6751 and NGC 6781. A planetary nebula has nothing to do with planets, but consists of the ejected atmosphere of a dead star illuminated by the white dwarf at its core. They are typically visible for just a few thousand years before they dissipate, and they seed the instellar medium with heavy elements which end up in the new stars and planets such as those in our Solar System. M27, the Dumbbell Nebula, is one of the most famous planetary nebulae, sitting below Aquila. Its shape can be seen through a small telescope, and a long exposure photograph will reveal its colours. It is one of the closest planetary nebulae to Earth at a distance of around 1300 light-years, and extends to a quarter of the diameter of the full Moon in the sky. The asterism known as the Coathanger is nearby.

The Planets


Odds and Ends

On July 4, the Hubble Space Telescope logged in its one millionth science observation. Looking at exoplanet Kepler 2b, HST made spectroscopic measurements in a search for traces of water.

The space shuttle Atlantis landed back on Earth on July 21, marking the end of the space shuttle era. Progress is being made by the companies contracted by NASA to build the next generation of spacecraft, with one company, SpaceX, hoping to dock an unmanned capsule with the International Space Station by the end of 2011.

Show Credits

News:Megan Argo
Interview:Dr Philipp Podsiadlowski and Mark Purver
Night sky:Ian Morison and John Field
Presenters:Megan Argo, Melanie Gendre and Jen Gupta
Editors:Jen Gupta, Megan Argo, Claire Bretherton and Mark Purver
Segment Voice:Liz Guzman
Website:Jen Gupta and Stuart Lowe
Producer:Jen Gupta
Cover art:Hubble Space Telescope image of the region surrounding supernova 1987A. CREDIT: NASA, ESA, and R. Kirshner (Harvard-Smithsonian Center for Astrophysics)

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