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September 2015: Banner

September 2015

In the show this time, we talk to Dr. Chris Gordon about mysterious gamma rays, Ian rounds up the latest news, and we find out what we can see in the September night sky from Ian Morison and Haritina Mogosanu.

The News

In the news this month: scrambled information escapes from Stephen Hawking, sunspot record is recalibrated and names on Pluto generate controversy.

Interview with Dr. Chris Gordon

Dr Chris Gordon is a senior lecturer at the University of Canterbury in New Zealand. His research currently focusses on identifying the nature of dark matter using astronomical observations. He talks to Monique about self-annihilating dark matter, which may explain the excess gamma ray signal detected at the centre of our galaxy.

Chris explains how self-interacting dark matter models fit with our current understanding of dark matter. Some supersymmetric models naturally predict weakly interacting particles that would be good candidates for dark matter and these are currently being searched for at the Large Hadron Collider .

Another potential explanation for the observed gamma ray excess is an unresolved population of millisecond pulsars. Chris discusses the evidence for this alternate explanation and mentions how the next generation of telescopes will offer an insight into the source of the observed excess. He concludes with a discussion of future dark matter searches, including observations of dwarf spheroidal galaxies and direct detection experiments.

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during September 2015.

The Stars

To the south and moving westward as night progresses you may see the Summer Triangle: the bright stars Deneb (in Cygnus), Vega (in Lyra) and below them Altair (in Aquila). Towards the south later in the evening you may spot the great square of Pegasus - adjacent to Andromeda and M31, the Andromeda Nebula. To the north lies "w" shaped Cassiopeia and Perseus. Between the two, close to the Milky Way, try to spot the Perseus Double Cluster with a goods pair of binoculars. You might also spot M33 may also be visible on a transparent night with a good pair of binoculars.

The Planets

The Moon

On September 4th and 21st you may spot The Alpine Valley, a cleft across the Appenine mountain chain. It is about 7 miles wide and 79 miles long and a thin rill runs along its length which is quite challenging to observe.


Southern Hemisphere

Haritina Mogosanu from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during September 2015.

The Milky Way

At the beginning of springtime here, the Milky Way spans the sky from north to south going through Zenith. From there, the fish hook of Maui slowly starts to drag the Milky Way down from the sky and towards the western horizon, all night long so that night after night the center of the galaxy appears lower and lower in the evening sky. Here, in the Southern Hemisphere, we are very lucky to see the Milky Way in all its brightness and beauty.

The Stars

Many of the brightest stars are scattered along or near the Milky Way. Starting from North is Albireo, the beautiful orange and blue double star, in the constellation of Cygnus or the Northern Cross. On the left hand side and close to the Milky Way lays Vega, due north at dusk and setting in the late evening. On the right hand side, a celestial dolphin flips from the galactic river, revealing its two famous stars Sualocin and Rotanev- the anagram of the astronomer Nicolaus Venator! Just a few degrees higher up in the sky than the dolphin, the Eagle is flying Altair towards the galactic river. Keep lifting your head up and follow the Milky Way. With a telescope powerful enough, you will find Pluto right there near the Teapot’s handle in Sagittarius, but at 14 magnitude you would need a large aperture telescope (of 10 inches or more) to see it, as well as great star charts to pinpoint it. If Pluto is not an easy target, the fish hook of Maui in Scorpius is home of the bright star red giant Antares or Rehua in Maori. In between Sagittarius and Scorpius there are beautiful deep sky objects and now is a great time in the southern hemisphere to hunt for them. They include the Lagoon Nebula, the Omega Nebula, also known as the Horseshoe Nebula or Swan Nebula; and the Trifid Nebula.

To find directions in the Southern Hemisphere all we need to do is to follow the arch of the Milky Way. On it, midway down the southwest sky almost opposite Altair, are ' The Pointers ', Beta and Alpha Centauri. They point down to Crux the Southern Cross. There are about 27 ways to find South here and most of them involve the Southern Cross. As a circumpolar constellation, at the beginning of the spring's evening sky, Crux appears almost in the 3 o'clock position on the 60 degrees declination circle. Inside it, the brilliant Jewel Box, discovered by Nicolas Louis de La Caille and baptised so by John Herschel, or NGC 4755, is an open cluster of stars. At the center of it, a blue giant, a red giant, and another blue giant star align to make the more modern asterism of the 'traffic light'. But of course you will need a telescope to see this.

Globular Clusters

The Moon and Planets

In Maori the Moon is called Marama which literarily can mean the white (ma) light (ma) coming from the sun Ra. The harbinger of this spring is a supermoon. A supermoon happens when the full moon coincides with when the Moon is closest to Earth, also known as perigee. Supermoons occur every fourteenth full Moon.

Mercury Whiro and Saturn Pare -a -Rao are bright planets in the evening sky. At the beginning of the month Mercury is making its best evening sky appearance of the year, low in the west. Cream-coloured Saturn is northwest of the zenith at dusk and midway down the western sky by late evening. Brilliant Venus, 'Kopu Rere Ata' is the 'morning star' for Maori, rises in the east two hours before the Sun. A telescope shows Earth-sized Venus shining as a thin crescent from 60 million km away. On 21 of September Venus displays its greatest illuminated extent as the morning "star" This means that for the next several mornings, our morning star Venus will be shining at or near its greatest brilliancy.

Odds and Ends

The closest collisional ring galaxy to the Milky Way has been discovered, at a distance seven times closer than the previous known nearest galaxy of this type. Galaxies of this type arise when two galaxies interact in a near 'bulls-eye' collision. The resultant shockwaves from the collision compress the gas within the colliding pair and kick off a new epoch of star formation, forming a ring of bright emission in the merge galaxy making it look like a Catherine Wheel. The discovery of this new object was made whilst the astronomers involved were actually searching the Southern Hemisphere sky for Planetary Nebula. The proximity of this new discovery suggests that these rare phenomenon may be a bit more common than was previously thought.

NASA's beloved Cassini mission is drawing to a close. The spacecraft, which has brought us scientific insight as well as countless magnificent images of the Saturnian system, is set to end in 2017 with a terminal dive into the atmosphere of Saturn. Dione, Saturn's 4th largest satellite (by surface area), has just been visited for the last time by Cassini and has returned a wealth of beautiful images to Earth. Flying as low as 474 km, the surface is resolved to roughly 10 metres per pixel, showing some of the finer crustal features of the moon such as small craters, crater ridges and cliff edges. Other images, taken from a range altitudes show, within its barren icy terrain, its biggest impact sites illuminated by the Sun and the soft glow of Saturn. From the approach and recession of Cassini, Dione has Saturn and its wafer-thin rings as a beautiful backdrop. The raw, unprocessed images are available here. Cassini is now en-route to Titan and will spend the rest of this year bouncing between it and Enceladus before starting its final full year of science before its 2017 final descent through Saturn's cloud tops.

Show Credits

News:Ian Harrison
Interview:Dr. Chris Gordon and Monique Henson
Night sky:Ian Morison and Haritina Mogosanu
Presenters:Adam Avison, George Bendo, Benjamin Shaw
Editors:Benjamin Shaw, George Bendo and Charlie Walker
Segment Voice:Iain McDonald
Website:Indy Leclercq and Stuart Lowe
Producer:Indy Leclercq
Cover art:Saturn's moon Dione set against Saturn itself, with rings visible CREDIT: NASA/JPL-Caltech/SSI

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