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September 2014: Lost

September 2014

In this show, we talk to Dr Richard Shaw about detecting Baryon Acoustic Oscillations, Indy rounds up the latest news and we find out what we can see in the September night sky from Ian Morison and Claire Bretherton.

The News

In the news this month: early monster stars, and a new address for the Milky Way.

Interview with Dr Richard Shaw

Dr Richard Shaw works at the University of Toronto, and is participating in a project called the Canadian Hydrogen Intensity Mapping Experiment (CHIME). He explains how the custom-made CHIME telescope will detect radio emission from cold hydrogen in distant galaxies, and how this will be used to make measurements of the expansion of the Universe that complement those from the cosmic microwave background and from the observed distribution of galaxies in optical light. He also discusses how cosmological redshift allows us to distinguish the radiation emitted by hydrogen at different times in our Universe's history, and how such radiation can be separated from the the foreground emission of our own Milky Way that is a million times stronger.

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during September 2014.

The Summer Triangle consisting of the stars Vega, Deneb and Altair is still high in the sky. The asterism of the Northern Cross, near to Deneb, contains the multicoloured double star Albireo. Another double star, Epsilon Lyrae, can be found using binoculars near to Vega, and a telescope reveals that it is itself a pair of doubles. The constellation of Delphinus is below the Summer Triangle, with Aquarius and Capricornus further down still. The Square of Pegasus rises in the east as the evening progresses, and following the arc of the head of Pegasus leads to the globular cluster M15, while the top-left corner of the Square (or, alternatively, the topmost stars of Cassiopeia) can be used to locate the Andromeda Galaxy. Perseus is in the north-east, below Cassiopeia, and binoculars show that the Double Cluster, a pair of open star clusters, lies between them.

The Planets


Southern Hemisphere

Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during September 2014.

The spring equinox arrives this month, so the nights are rapidly getting shorter. The bright stars Vega and Canopus mark the northern and southern horizons at dusk, with the band of the Milky Way passing overhead between them. Vega is part of the Winter Triangle, along with Deneb and Altair. Between Vega and Altair is the lovely double star Albireo, marking the beak of Cygnus the Swan. The winter constellations of Scorpius and Sagittarius are sliding towards the western horizon night by night, with Orion rising opposite them as they set. Between them are Capricornus, Aquarius and Pisces.

Capricornus, often depicted as a cross between a goat and a fish, appears as an elongated triangle of stars, while a smaller triangle marks its head and horns. Its brightest star is Delta Capricorni or Deneb Algedi, and it changes significantly in brightness because it is an eclipsing binary, in which two stars partially block one another from our view as they orbit. The system is now known to contain four stars. Alpha Capricorni, or Algedi, is a double star whose members can just be distinguished with the naked eye, but the two stars are not in a binary system as they are at very different distances from us. The watery constellations in this part of the sky are associated with autumn and winter rains in the northern hemisphere, and to the south-east of Capricornus is Piscis Austrinus, the Southern Fish. The bright star Fomalhaut, marking its mouth, has a planetary companion that was directly imaged by the Hubble Space Telescope.

The constellation of Aquarius the Water-carrier, lying between Fomalhaut and Altair, contains a number of beautiful deep-sky objects. M2 is a globular cluster near to the third-magnitude star Beta Aquarii. Visible in binoculars, a telescope of 20 centimetres in aperture shows up individual stars. The Helix Nebula, or NGC 7293, is a planetary nebula positioned south-west of Delta Aquarii that appears as a hazy circle in binoculars. A telescope reveals the darker area in the centre, while a long-exposure photograph brings out the nebula's colours. Pisces, Cetus and Delphinus are more water-themed constellations in this area of the sky.

The Planets


Odds and Ends

Two of ESA's Galileo global navigation system hit a snag in August, when two of its satellites were placed into the wrong orbits. The European constellation, which will work alongside the American GPS and Russian GLONASS systems, should provide superior positioning accuracy of just one metre to ground-based receivers once all thirty satellites are in orbit in 2017. The fifth and sixth, however, are now in lower orbits than intended, and it is not clear whether they can be used within Galileo. The 70 kilogrammes of fuel aboard each satellite, intended to keep their orbits from gradually falling over the course of many years, may or may not be enough to reposition them.

New measurements of the distance to the Pleiades have reignited an argument between scientists on both sides of the Atlantic. American scientists, using the VLBA telescope array, have found a different distance to that measured by European counterparts using the Hipparcos space telescope. The issue is hoped to be resolved when the Gaia telescope finishes taking data.

Show Credits

News:Indy Leclercq
Interview:Dr Richard Shaw and Mark Purver
Night sky:Ian Morison and Claire Bretherton
Presenters:Indy Leclercq and Mark Purver
Editors:Indy Leclercq, Claire Bretherton, and Mark Purver
Segment Voice:Tess Jaffe
Website:Indy Leclercq and Stuart Lowe
Producer:Indy Leclercq
Cover art:A slice of the Laniakea supercluster in the supergalactic equatorial plane. CREDIT: Tully et al, Nature 513, 71-73

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