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April 2015: Opposites

April 2015

In the show this time, we talk to Dr. Cormac Purcell about The Gum Nebula, Indy rounds up the latest news, and we find out what we can see in the April night sky from Ian Morison and Claire Bretherton.

The News

In this month's news, we bring you updates from two planets at opposite ends of the solar system: Mercury, and the dwarf planet Ceres.

Interview with Dr Cormac Purcell

Dr Cormac Purcell from the University of Sydney has been researching the properties of the Gum Nebula. He talks to the Jodcast about magnetic fields in the Milky Way, why they are interesting, and how we can measure them. He explains why it is so difficult to measure our own galaxy's magnetic fields in comparison to those of distant galaxies, and how stars blow giant bubbles which may help solve this dilemma.

The Night Sky

Northern Hemisphere

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

Orion is sinking in the west as darkness falls, followed by Gemini and its bright stars Castor and Pollux. Further towards the south is the faint constellation of Cancer. It contains the Beehive Cluster, an open star cluster visible in binoculars, and currently plays host to the planet Jupiter as well. Leo is due south in the evening, with its bright star Regulus. Nearby, in Virgo and Coma Bernices, is an area called the Realm of the Galaxies. In this region, an 8" telescope can pick out a number of galaxies that are part of the Virgo Cluster, the largest cluster of galaxies in our local universe and itself part of a much bigger supercluster. Higher up is Boötes, with its bright star Arcturus, and overhead is Ursa Major. Later in the night, Lyra and its bright star Vega rise in the north-east.

The Planets


Southern Hemisphere

Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during April 2015.

The night of the 4th-5th sees the first lunar eclipse of the year, and also the backward move of the clocks in parts of the southern hemisphere. In Wellington, New Zealand, the penumbral phase begins at 22:03 NZDT (New Zealand Daylight Time, 13 hours ahead of Universal Time) as the Earth begins to obscure sunlight from the Moon's surface. The umbral phase, when sunlight is fully blocked from part of the Moon, starts at 23:17. The Moon is cast into total shadow for 7 minutes, from 00:57 to 01:04. The umbral phase ends at 02:44, while the penumbral phase finishes at 02:58 NZST (New Zealand Standard Time, 12 hours ahead of Universal Time).

The Moon is in Virgo during the eclipse, about halfway between Jupiter in the north-west and Saturn in the east. Venus appears brightly in the evening, and sets 2 hours after the Sun by the end of the month. Saturn is in Scorpius, a little below the red star Antares. It rises around 22:00 NZDT at the beginning of the month and 19:00 NZST at the end.

The constellation of Centaurus is high in the east after dark, with its two brightest stars, Alpha and Beta Centauri, pointing towards Crux, the Southern Cross. Centaurus is one of the largest constellations and contains many bright stars, clusters and nebulae. The globular cluster Omega Centauri, the largest and brightest in the Milky Way Galaxy, appears similar in size to the full Moon when seen with the naked eye at magnitude +3.7. Binoculars reveal individual stars and a dense core. With a population of stars that are around 12 billion years old, it is a relic of the early Universe and may be the remnant of a dwarf galaxy that merged with the Milky Way. NGC 3766 and NGC 5460 are two open star clusters in Centaurus, both just visible to the naked eye. The planetary nebula NGC 3918, the 'Blue Planetary', is also located there, and, at magnitude +8, its blue oval shape can be seen with a small telescope. Centaurus hosts one of the closest galaxy clusters to Earth. Separately, it is home to NGC 5128, the galaxy known as Centaurus A. Centaurus A is elliptical, but has a dark dust lane across the middle, and the supermassive black hole at its heart is thought to be consuming a spiral galaxy with which it has merged. As a result, it emits relativistic jets that can be detected at radio and X-ray wavelengths. Located less than 5° from Omega Centauri, Centaurus A is the fifth-brightest galaxy in our sky (excluding the Milky Way) and is easily visible in binoculars. The bright central bulge and dark lane may be viewed with larger binoculars, while a telescope reveals more of the galaxy's structure.

Odds and Ends

NASA's Mars Exploration Rover Opportunity has completed the very first Marathon distance of any human-made device on another planet. The Rover completed the 26.219 mile distance in 11 years and 2 months.

Astronomers studying the properties of dark matter have found that the mysterious stuff doesn't interact with itself. Studying cluster mergers using Hubble and Chandra X-ray observations, the scientists found that when two clumps of dark matter collide, they simply pass right through each other. The other significant result is a statistical detection of dark matter with a very high probability: it is more than 99.99999999999% likely that dark matter is present in the clusters studied. What it actually is, remains to be seen.

The discovery of an aurora and a mysteriously high altitude dust cloud in the Martian atmosphere by NASA's MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft has surprised planetary scientists. Neither of these phenomena have been predicted by current models of the Martian atmosphere or by any of the known processes which occur on Mars. The aurora was much deeper than any seen on Earth, implying the particles responsible must be very energetic, most probably originating from the Sun. Mars is much more vulnerable to solar particles than Earth as it lost its protective magnetic field billions of years ago. This allows the energetic solar particles to strike through the atmosphere creating aurora closer to the surface. The origin of the dust cloud is much more uncertain. It is possible it has risen from the atmosphere; been transferred by Mars' moons Phobos and Deimos or come from solar winds blowing dust from passing comets. The full story can be found here.

Show Credits

News:Indy Leclercq
Interview:Dr Cormac Purcell and Indy Leclercq
Night sky:Ian Morison and Claire Bretherton
Presenters:Indy Leclercq, Josie Peters and Christina Smith
Editors:Indy Leclercq, Mark Purver and Charlie Walker
Segment Voice:Iain McDonald
Website:Benjamin Shaw and Stuart Lowe
Website:Benjamin Shaw and Stuart Lowe
Cover art:Computer generated image of the Gum Nebula. CREDIT: Wikimedia Commons

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