We're back from our summer break with an interview with Professor Rod Davies about anomalous microwave emission. As ever we have the latest astronomical news, what you can see in the September night sky, and your feedback.
In the news this month:
- In 2004 the Stardust spacecraft flew past the comet Wild-2, passing through the dense gas and dust surrounding the nucleus on January 2nd. Using a special collector containing a grid of aerogel, the probe sampled the particles in the comet's tail, later returning them to Earth in a capsule which parachuted back into the Earth's atmosphere on January 15th 2006. Over the last three years, scientists around the world have been analysing the particles collected in the aerogel samples to investigate the chemical composition of the comet. Preliminary results, published in the journal Science in December 2006, showed the presence of various organic compounds in the returned samples. While the presence of some of these compounds may have been due to contamination of the aerogel during manufacture of the spacecraft, a comparison analysis of flight spares - aerogel samples which were manufactured at the same time and in the same way but never flown - showed a lower abundance of these chemicals, indicating that at least some of the organic material came from the cometary debris. One such chemical was the amino acid glycine. Preliminary results showed that it was present in some samples, but were not conclusive enough to show that it came from the comet rather than from contamination. In new results presented at a meeting of the American Chemical Society in Washington DC during August, a team have determined that amino acid was present in cometary material collected by the Stardust mission. Glycine is an amino acid used by living organisms to make proteins and one of the fundamental building blocks of life as we know it, so finding this sort of molecule in space could have implications for the abundance of life in the universe. Led by Jamie Elsila at NASA's Goddard Space Flight Centre, the team conducted isotopic analysis of the samples to try and determine the origin of the chemical. Organic compounds contain carbon atoms, but not all carbon is the same. Different isotopes exist with the same number of protons but different numbers of neutrons, giving the carbon atoms slightly different weights. Carbon-12 has six protons and six neutrons in it's nucleus, while carbon-13 has an extra neutron and is slightly heavier. Glycine molecules from Earth contain less carbon-13 than those from space, so measuring the relative amounts of each isotope in a sample can distinguish between glycine from Earth-based contaminants and glycine from comet debris. As molecules of gas passed through the aerogel, some of them stuck to the aluminium foil lining the sides of the tiny chambers that hold the aerogel in the collection grid. The team analysed traces of material from the foil and had to refine their equipment to make it accurate and sensitive enough to analyse such tiny samples. Their results show that the glycine returned by Stardust has an extraterrestrial carbon isotope signature containing more carbon-13 than samples from Earth and ruling out contamination. The results have been accepted for publication in the journal Meteoritics and Planetary Science.
- The problem of determining the sequence of events during the formation of the early solar system is one that requires knowledge of the precise timescales for the physical and chemical processes occurring in the accretion disk. In a similar way to the carbon dating of artifacts here on Earth, there are processes which can be used to date events in the early solar system. One such commonly used technique relies on the radioactive decay process of aluminium. Stable aluminium atoms have an atomic mass of 27 but one isotope, aluminium-26, is relatively short-lived, decaying to magnesium-26 with a half-life of 730 thousand years. Compared to the age of the solar system, some five billion years, this is a relatively short time period, so all of the original aluminium-26 in the early solar system must now have decayed. The origin of the aluminium-26 is not certain. It may be that it was present in the cloud from the start, created in a nearby supernova explosion, or generated within the solar system itself. Careful analysis of the isotopic composition of meteorite samples can yield a sequence of events, but the accuracy of this method relies on the assumption that the original aluminium-26 was evenly distributed around the solar system. If it was generated by a source outside the solar system then it may not have been well mixed with the rest of the material in the nebula, resulting in unreliable age estimates. In research published in Science on August 21st, Johan Villeneuve and colleagues at Nancay university in France, describe new techniques they have developed which allow very precise measurements of magnesium isotopes. Comparing samples from different objects, the researchers show that the Earth and several components of primitive chondritic meteorites all lie on the same evolutionary line. Their analysis confirms that the ratio of radioactive aluminium-26 to stable aluminium-27 was uniform in the early solar system, confirming that this process is a reliable chronometer of events at that time.
- Stars come in a variety of sizes. Many are of a similar size to our own Sun, but there are plenty of stars which are much, much larger. For every star that is 20 times the mass of our Sun, there should be roughly 500 stars with the Sun's mass or less. The trouble with studying stellar populations, however, is that the brighter stars often outshine their dimmer companions, making it hard to determine how many stars of each type there are in a given star cluster or galaxy. For some time, the standard assumption has been that there is a simple function relating how many stars of a each type are present in a given cluster. This relationship is known as the stellar initial mass function. The idea is that if the population of large stars is measured, then this relationship can tell you about the rest of the stellar population, the dimmer stars that can't be seen directly. But a recent study, published in the Astrophysical Journal, has thrown doubt on this long held and widely used assumption. This is not the first such study, but these new results provide extra information which adds to the picture. Led by Gerhardt Meurer, at Johns Hopkins University, the researchers used a combination of optical images from telescopes at the Cerro Tololo Inter-American Observatory in Chile and ultra-violet observations from the GALEX satellite to show that many galaxies do not form a lot of massive stars yet still have plenty of lower mass counterparts. The ultra-violet images are sensitive to somewhat small stars, 3 or more times more massive than the Sun, while the filtered optical images are only sensitive to the largest stars with 20 or more times the mass of the Sun. The problem is particularly severe in more diffuse, faint galaxies. The initial mass function would predict a certain mass for the stellar content of the galaxy based on the light visible from the larger stars, but these new results show that there may be far more faint stars in such galaxies than was previously thought.
- And finally.... August 25th saw the 400th anniversary of the day when Galileo Galilei first showed his improved telescope design to government officials in Venice. Although he did not invent the telescope, he heard of the idea and improved upon it, showing it to the senate as a means of strategic advantage in battle, allowing their armies to see distant enemy ships long before they reached shore. It was still some months before he turned the device to the heavens and made his famous drawings of the planet Saturn. Telescopes have come a long way in the intervening years. August also saw the opening of the world's largest telescope, the Grand Telescopio Canarias or GTC, located on La Palma in the Canary Islands. With a 10.4-m mirror, made up of 36 hexagonal segments, the GTC is larger than any other current ground-based optical telescope. Originally scheduled to open in 2003, the project has taken somewhat longer than expected but it may provide a useful testbed for technologies planned for the next generation of optical telescopes with mirrors 25 metres and more in diameter.
Professor Rodney Davies (Jodrell Bank Centre for Astrophysics) talked to us about anomalous emission and spinning dust.
The Night Sky
Ian Morison tells us what we can see in the night sky during September 2009.
Now becoming visible towards the south east in the early evening is Pegasus - the winged horse. If you start at the top left-hand star of the square of Pegasus - Alpha Andromedae - you curve up to the left two bright stars then turn sharp right, move one reasonably bright star and then carry on by just about the same amount to the fuzzy glow of the Andromeda Galaxy (M31). Another way to find Andromeda is to find the 'w' shaped constellation of Cassiopeia. The three bright right-hand stars form a 'v' which points down to the Andromeda Galaxy too. Heading left from Cassiopeia brings you towards the constellation of Perseus and between them is the Double Cluster in Perseus. Below the bright star Alpha Persei is the eclipsing binary Algol. Below Perseus is Pisces with Aquarius to the lower right and Cetus to the left.
- Jupiter, now lying in Capricornus, becomes more easily visible this month rising soon after twilight.
- Saturn, sadly, has virtually become lost in the Suns glare and will not be seen again for a month or so when it reappears in the pre dawn sky. This is a pity as, on September 4th, its rings a edge on to the Sun and so are not illuminated and thus disappear. It is just possible that on the 4th, given a very low western horizon, you might just be able to spot it 2 degrees above the horizon at 8pm BST. Do not search for it with binoculars or a telescope until after the Sun has set!
- Mercury passes behind the Sun (called inferior conjunction) on the 20th September so it will not be visible until the very end of the month in the dawn sky - and then with difficulty.
- Mars is becoming more prominent in the morning sky rising at about midnight BST during the month. It lies in the constellation Gemini and is close to the open cluster M35 at the beginning of the month.
- Venus is now moving towards the far side of the Sun and so getting closer in angle to it. It will thus be best seen at the beginning of September as it lies in the constellation Cancer, just below the Beehive Cluster, M4. During the month it moves down into Leo where, on the 20th, it will be just half a degree to the upper left of Leo's brightest star, Regulus.
- At the beginning of last month you could observe Jupiter with apparently 5, not 4, moons! On the night of the 2nd/3rd September between 04:45 and 06:29 UT, sadly after Jupiter has set as seen from the UK, Jupiter will appear to have lost all its moons. Ganymede and Europa will lie in front of Jupiter, Io will be behind, and Callisto will be in Jupiter's shadow. This is the last time that Jupiter will appear moonless until 2019.
- Late in the evening on the 12th of September, the Moon passes just 0.5 degrees to the left of the open cluster in Gemini, M35. As both the Moon and the cluster have apparent angular sizes of ~0.5 degrees it means that the Moon will just skim past the edge of the cluster.
- Around new Moon on 18th September you may see Uranus and spot the asteroid Juno. Uranus is at opposition on September 17th and will have a magnitude of +5.7 lying just below the circlet of Pisces which itself lies below the square of Pegasus.
- Neptune passed opposition (and hence due south around midnight UT) last month and so will be seen in Capricornus towards the south in the late evening during September. It lies just over 2 degrees above the +2.8 magnitude star Delta Capricorni - so will be easily spotted using binoculars at magnitude +7.8 towards the top of the field of view if the star is placed in the lower centre of the field.
Looking to the north you'll see many stars that are also seen in the northern hemisphere. Looking south you'll see the lovely vista of the Milky Way. Due south is the south celestial pole with the Large and Small Magellanic clouds to the left. In the plane of the Milky Way, about a third of the way up from the horizon, you see Crux - the Southern Cross. If you look at the highest of those stars with binoculars, you'll find the nearby Jewel Box Cluster. Above that is the constellation of Centaurus. Take the lower of the two brightest stars, and then work your way to the west and you'll come to another bright star. If you carry on in that direction you should see a fairly bright fuzzy object which is globular cluster Omega Centauri.
Odds and Ends
Jamx mentions Microsoft gifting the Feynman lectures to the world.
|Noticias en Español - Septiembre 2009:||Lizette Ramirez|
|Interview:||Prof Rodney Davies and Stuart Lowe|
|Night sky this month:||Ian Morison|
|Presenters:||Stuart Lowe and Neil Young|
|Henry Jones, Snr:||Ashwath Ganeshan|
|Marcus Brody:||David Ault|
|Sarah Connor:||Gwendolyn Jensen-Woodard|
|Segment Voice:||Danny Wong-McSweeney|
|Cover art:||The 'duck' seen in IRAS 100 micron data CREDIT:: IRAS|