INSTITUTE OF PUBLIC OPEN EVENING WEDNESDAY 16TH JANUARY 2013

After all the excitement of Stargazing Live, welcome back to the more usual form of our public open evenings. Tonight our speaker is SARAH SMEDLEY, who’ll be PLAYING PINBALL WITH STARS. The talk begins promptly at 7.15pm and lasts for about half an hour; it will be followed by an opportunity to observe if (and only if…) the sky is clear. Two of the historical telescopes will be open, and the CAMBRIDGE ASTRONOMICAL ASSOCIATION will provide a floorshow on the observatory lawns relaying live images from three modern telescopes. If we’re unlucky and it’s cloudy, then we’ll offer you a cup of tea and the CAA will give more astro-information afterwards in the lecture theatre for those who want to stay on. The talk schedule for this winter season is listed on our outreach website at: www.ast.cam.ac.uk/public/public_observing/talks2012-13 and we TWEET current astr0-news and events as IOACOA. Next week’s talk will be given by JONATHAN CRASS who’ll be telling us how THE DEVIL'S IN THE DETAIL - HIGH RESOLUTION IMAGING IN ASTRONOMY. If you have any questions or comments about the IoA Open Evenings, please get in touch with CAROLIN CRAWFORD [email protected]

The Cambridge Astronomical Association will be holding their monthly speaker meeting this FRIDAY 18TH JANUARY at 8pm, here in the Sackler Lecture Theatre: the topic is A HITCHHIKER’S GUIDE TO SOLAR ECLIPSES, and the talk will be given by Ithel and Omara Williams. Everybody is welcome.

THE LARGEST SPIRAL Observations of a large spiral galaxy - catalogued as NGC 6872, and lying about 210 million light-years distant from Earth – have revealed that it is much larger than previously realised. Observations taken in the UV are particularly sensitive to the light given off by newly-formed massive stars, and UV images of this galaxy show a host of young stars far from the galaxy centre, and at the very end of a long tidal tail of such stars. This takes the galaxy’s total armspan to some five times wider than that of the Milky Way, and to around 520,000 light-years. The recent star formation has been triggered by a much smaller galaxy blundering through the gas clouds in the spiral arms of NGC 6872 around 130 million years ago; this collision set a wave of star formation pulsing through the larger galaxy’s disc. The intruder galaxy can be seen as a lens-shaped object lying just above the centre of the spiral galaxy. The gravitational forces in the interaction will have helped with the stretching out of the galaxy, making it the biggest spiral galaxy yet seen. The largest star formation region (ringed in the image) is lit up by the radiation from some of the hottest and youngest stars (less than 200 million years old). This area is sufficiently remote from the bulk of the rest of the galaxy that it is expected to break away to form a separate, and new, dwarf galaxy.

THE OLDEST STAR IN THE UNIVERSE? HD 140283 appears as just a normal star (an artist’s impression shown to the right), around 186 light-years away. However, it’s just been calculated to be at least 13.2 billion years old – given that the age of the whole Universe is 13.77 billion years, this means it must have formed within 600 million years of the Big Bang. But this does beg the question – how do you find the ‘age’ of a star? HD 140283 is a ‘sub-giant’, meaning that it is currently in a later stage of its evolution; it has just about exhausted the supply of hydrogen at its core and switching to burning helium – and in this phase, the star's slowly dimming luminosity is a highly sensitive indicator of its age. The very first stars to condense in the primordial Universe would have been made only of hydrogen and helium – all heavier elements are created through nuclear fusion at their cores, and then scattered into space when this first generation of massive stars exploded at the end of their lives. The fact that HD 140283 contains not just hydrogen and helium, but also a smattering of heavier elements, indicates that it is most likely from a second generation of stars to have formed. The early age of HD 140283 hints that the delay between the first and second generations might have been much shorter than previously realised, perhaps only a few tens of million years.

INTRODUCING A SPECIAL NEW … And this exoplanet is special as one of its co-discoverers is our very own Paul Fellows from the CAA. It was identified as part of the Planet Hunters ‘’ initiative, which encourages members of the public to use data from the Kepler satellite to try and spot the characteristic and regular dips in the brightness of a star that could be caused by a planet moving in front of it. The host star is about 80% of the 's size, but the planet itself is about 4.6 larger than the Earth (about the same as or ). It orbits the star every 397.5 (Earth-)days at a radius just beyond that of the Earth round the Sun. At this distance the planet should be a slightly chilly -30° C, but could be a slightly warmer if it has an atmosphere to create a slight greenhouse effect. This is just one of 31 planet candidates that have been discovered by Planet Hunters. Want to discover your own exoplanet? Have a try at www.planethunters.org!

… AND EARTH’S CLOSEST TWIN YET Another new planetary candidate found by Kepler seems to be the closest match yet found to Earth. With a radius only 1.5 times that of the Earth, the potential planet KOI 172.02 is likely to have a similar gravity to Earth at its surface. Its orbit lasts 242 days, giving its distance from its host star as safely within the ‘habitable zone’ - meaning it is at the right distance for any water on its surface to be liquid, a prime consideration for a planet to host life. It’s the first Earth-like planet found in orbit around a Sun- like (only slightly cooler) host star. KOI 172.02 is just one of 460 new planetary candidates announced by the Kepler science team, bringing their total to 2,740; this includes a dramatic increase in the number of Earth-sized and super -Earth-sized planets discovered. However, further measurements and observations are required to confirm the Kepler identifications as real . The most up-to-date analysis of all the Kepler data suggests that almost every such Sun-like star could have at least one planet, and that there are likely to be somewhere in the order of 17 billion planets in the Milky Way that are Earth-like in size.

WEATHER ON A BROWN DWARF A brown dwarf is a curious kind of object – it has too much mass and is too hot to be a planet, but neither is it a proper star. We don’t know very much about them – they are difficult to study, being both very small and very dim. Generally brown dwarfs are regarded as ‘failed stars’, that may resemble giant gas planets with deep and complicated atmosphere. Evidence in support of this view has been offered by astronomers who used both the Hubble and Spitzer space telescopes to study the turbulent atmosphere of one cool brown dwarf in detail. Spitzer and Hubble each observe a different layer within the atmosphere - certain infrared wavelengths are blocked by vapours of water and methane high up, while other infrared wavelengths emerge from much deeper layers. The brightness of the star varied with time as it rotated every 90 minutes or so, bringing different patches of atmospheric material into and out of view. This indicates that there are large storms within the upper layers of the brown dwarf, creating planet-sized clouds that are driven through the atmosphere by strong winds.

A GIANT SPOT ON THE SUN TODAY The Sun goes through periodic changes in its activity over an 11-year cycle, which can be tracked by the level of radiation it emits, the frequency of the flares it gives off, and the number and location of sunspots on its surface. We’re now in a period of maximum Solar activity, so it’s no surprise that there’s currently a giant sunspot region (catalogued as AR 1654 and shown right) stretching many tens of thousands of miles across the Solar disc. Sunspots are magnetically active regions, and appear dark only because they are cooler compared to the surrounding regions (at temperatures of around 3300°C rather than at 5500°C). They also mark the regions responsible for the giant eruptions that release intense bursts of energetic radiation and charged matter out into interplanetary space as solar flares. The sunspot region is still growing and changing, and we’ll just have to hope that it stays nice and calm while it’s pointed so directly at us!