April 2009: Goodbye

It's a very sad day for the Jodcast as it is Nick's last episode, after a glorius three and a half years of Jodcasting. To lighten the mood we've got a very special intro and outro and Dave makes a return after his six months in India. In this episode we also hear about finding planets with the upcoming LOFAR radio telescope from Dr Ian Stevens.

We start the show with a correction to the previous epsiode. A listener has pointed out that the International Space Station did not have a narrow encounter with a fragment from the Iridium 33/Cosmos 2251 collision but rather space debris "25090/1993-32D, which is probably a yo weight from the PAM-D stage that launched GPS 37 (IIA-20) in 1993 May". We're glad we got that sorted out.

The News

In the news this month:

• Strongest evidence yet for a binary black hole system. The number of galaxies observed colliding and merging is large. Catching the central supermassive blackholes before they merge is difficult because they are most likely to be found in distant quasars where current telescopes lack the resolution to work out what is going on directly. Astronomers studying the optical spectra from a large catalogue have found convincing evidence for two supermassive black holes in orbit. Observations of the system - J1536+0441 - were published in Nature by Boroson & Lauer (2009).
• Galaxy clusters are rough environments. Astronomers studying a large cluster of galaxies in Perseus have discovered a population of small galaxies that have survived in-tact despite the surrounding tug-of-war. The team found old, dwarf galaxies appearing smooth and round rather than gravitationally disrupted as expected. One explanation for this result is that these dwarf galaxies may contain a large amount of dark matter which cushions them from the surrounding gravitational forces. The research is published in MNRAS by Penny et al (2009).
• While supernovae are rare in our galaxy, many are discovered in other galaxies every year. Identifying the star which explodes is a tricky task. A study published in Nature (Gal-Yam & Leonard 2009) describes how the projenitor of SN 2005gl has been identified. Comparing HST images taken between 1997 and 2007, the projenitor was probably a very bright type of star known as a luminous blue variable (LBV). Apart from the exceptional case of SN 1987a, this is the most convincing case of the identification of a supernova projenitor.
• March 6th saw the launch of NASA's Kepler Mission. The spacecraft will go into an Earth-trailing orbit with a period of 372.5 days so that it slowly falls behind the Earth as it orbits the Sun. Over the 4 year mission, the highly sensitive detector will look for transiting planets around other stars.

Interview

Dandan and Roy talked to Ian Stevens (University of Birmingham) about detecting planets at radio frequencies using the upcoming LOFAR radio telescope.

We can already detect planets - such as Jupiter - in our own solar system with radio telescopes and the expectation is that planets around other stars should also be strong radio emitters. However, given that they are so far away, we need very sensitive radio telescopes and special circumstances. If Jupiter was orbiting much closer to the Sun it would be a much brighter in radio waves and easier to spot. At the moment we don't have any detections but the hope is that by using low frequency radio telescopes it will be possible to detect them.

The Night Sky

Ian Morison tells us what we can see in the night sky during April 2009.

Northern Hemisphere

The nights aren't as long now but after sunset you can still see the lovely area surrounding Orion and the bright star Sirius just west of south. Leo holds centre stage and contains Saturn at the moment. If you do have a small telescope there are some very nice galaxies that are just below the body of Leo. Between Gemini and Leo is the constellation of Cancer, The Crab. With binoculars, or unaided eyes under dark skies, you'll see a very nice star cluster known as the Beehive Cluster. Over to the lower left of Leo is a fairly empty patch of sky containing the star Spica in the constellation of Virgo. In Virgo and Coma Berenices you can find the region known as the Realm of the Galaxies.

Jupiter is not easily visible this month in the pre-dawn sky but will lay very close to the crescent Moon on April 19th. Mars is still close in angle to the Sun in the pre-dawn sky so isn't going to be high above the horizon although it will be reasonably bright. Venus is also in the pre-dawn sky and will be nicely visible close to a thin, waning crescent Moon on April 22nd.

Highlights

• On the night of April 22nd/23rd is the Lyrid meteor shower peaking in the early morning. It isn't very spectacular although the peak of activity is just before new Moon.
• On April 26th Mercury is at its greatest elongation. It remains in the sky after sunset for about 2 hours.
• Also on 26th April, the Moon is going to be very close by and later in the evening it will occult some of the stars in the Pleiades Cluster.
• Saturn is below Leo at magnitude +0.6

Southern Hemisphere

Venus is rather high above the horizon so there is a good chance to see it. The Magellanic Clouds are reasonably high in the south and are arcing around the south celestial pole and moving towards the horizon but as they do the Milky Way rises upwards. Scorpius and Sagittarius are rising in the south-east and they are beautifully rich areas to look at.

Odds and Ends

On the Forum there is a discussion about your favourite Jodcast cover art.

We get Dave on the phone to find out about his six month tour with an open-air production of Shakespeare's Measure for Measure in India. We also said goodbye to Nick, after three and a half years of service, with a special Jodcast quiz. Nick says he will try to come back and visit us when he can.

In case you haven't yet realised, our intro and outro take-over by Astronomy Cast was an April Fool. On April 1st you could even see this page in the style of Astronomy Cast. Was anybody fooled?

Show Credits