Institute of Astronomy Public Open Evenings WEDNESDAY 4TH NOVEMBER 2009

Welcome to the public open evenings at the Institute of Astronomy! Tonight there will be a talk starting promptly at 7.15pm, followed by an opportunity to observe with both modern and historical telescopes if and only if the weather is clear. Two of the historical telescopes will be open, and the CAMBRIDGE ASTRONOMICAL ASSOCIATION will be providing a floorshow on the observatory lawns relaying live images from three modern telescopes. We are open on Wednesday evenings now until the end of March. The talk schedule for the coming term can be found at : http://www.ast.cam.ac.uk/public/public_observing/0910/timetable.html

If you have any questions, suggestions or comments about the IoA Open Evenings please get in touch with CAROLIN CRAWFORD [email protected]

THIS WEEK’S TALK : Robin Catchpole will be introducing you to Light and Colour in Astronomy NEXT WEEK’S TALK : Debora Sijacki is discussing Supermassive black holes; monsters lurking in the hearts of

MORE ON MESSENGER AT This week has seen the release of some more scientific results from the Messenger spacecraft’s third and final flyby of Mercury at the end of September. Surprisingly, despite the scorchingly-hot due to being so close to the , and having little of its own, Mercury has an , albeit an incredibly tenuous one. The only way we expect that it can retain any kind of atmosphere is if there is a continual supply of material replenishing it – most likely from the wind of charged particles from the Sun blasting the planetary surface to knock out atoms. such as those of sodium, calcium and magnesium. By tracing the distribution of such atoms above the surface during the fly-by, Messenger has shown how this thin atmosphere extends to a tail behind the planet, where it is most sheltered from the bright sunlight. Interestingly there were variations in the amount of these atoms between the three flybys, suggested that there are seasonal changes in the atmosphere of the Mercury during its orbit around the Sun. This helps us better understand how the surface material could generate the atmosphere in the first place, and how it may have changed with time. The Messenger team have also directly measured the amounts of various elements on the planetary surface, and find there are much higher concentrations of heavy metals, such as and titanium – meaning we may have to rethink some of the current models of planetary formation. Now a full 98% of the planet’s surface has been mapped, and we wait while Messenger is swinging round to return to orbit and study the planet further in 2011. Browse the pretty pictures at: http://www.nasa.gov/mission_pages/messenger/multimedia/

FLYING OVER ENCELADUS Incidentally, on Monday the Cassini spacecraft also completed a flyby, one of a series flying close above the surface of Enceladus, the large icy moon around Saturn. This particular flight spent a minute passing through the heart of one of the plumes jetted out into space from Enceladus’s ice geysers (see one of the new images of these plumes on the right). The aim of this was to analyse the composition, , size and charge of the particles contained in the plumes, and thus determine more about how they are generated.

SEARCHING FOR OTHER EARTHS Those of you who have attended some of our talks about finding planets around other may remember mention of the launch of the Kepler spacecraft earlier this in March. So far astronomers have discovered gas giants, ice giants and ‘super-Earths’ elsewhere in the Milky Way, but terrestrial planets have proven elusive. Kepler’s mission (should it choose to accept it...) is to find such objects – particularly those that would lie in the ‘Goldilocks zone’, at the right distance from their host for liquid water – and potentially, life – to exist there. Ideally, we would love to be able to make an accurate estimate of how many of the millions of stars in our might have such planets. However, there’s now a glitch in the electronics on Kepler which means we might have to wait a little longer than anticipated to have our answer to this question. Indeed, a repair of the software has to be scheduled, which will mean the telescope probably won’t be able to detect any Earth-sized planets till 2011. So maybe we’ll now not make the discovery of the first Earth-like planet from space, but from one of the many exciting projects using imaginative instrumentation on ground-based telescopes instead!

SKY MAP FOR 8PM ON THE 4TH NOVEMBER courtesy of http://www.heavens-above.com/ SO WHAT’S IN THE SKY THIS WEEK? o We have a full MOON dominating the night, making it difficult to see all but the very brightest features in tonight’s sky. o JUPITER is very easy to identify as the brightest ‘star’ in the sky low down to the South during the first half of the night. o VENUS is very low in the eastern sky at dawn, and will rapidly be lost in the twilight over the next week. o If you are a very late-night person, you can observe MARS, which rises after about midnight o We are just reaching the peak of the TAURID METEOR SHOWER, where shooting stars can be seen coming from the approximate direction of the Pleaides in the of Taurus the bull. This can be found well to the upper right of the more recognisable Orion, and will be just to the right of the Moon on tomorrow night, the 5th November (ah, yes, there may be a few competing shooting stars that night...). Even though there aren’t many meteors expected (at very best, it’s about five to ten an hour), they do tend to be ‘fireballs’, much brighter and slower than usual. Unfortunately the best time to watch will not be till around midnight, but it’s certainly worth keeping an eye for any earlier as well. The material raining down on our atmosphere to cause these meteors originates from the trail of debris left in the wake of Comet Encke. ST JOHN’S COLLEGE LIBRARY ARE (STILL) CELEBRATING ASTRONOMY St John’s library will be holding an exhibition celebrating the contributions made to Astronomy by the College over the . The displays include medieval manuscripts, 18th century astronomical instruments, archival photographs, and the papers of Johnian astronomers, such as John Couch Adams (who played an important role in the discovery of the planet Neptune). The exhibition is open to all, and continues till the 21st December. Find out more at http://www.joh.cam.ac.uk/library/special_collections/hoyle/future_events/

56 Andromedae is a in the constellation Andromeda. Its apparent magnitude is 5.69. This binary system is composed of two yellow giants and is located near the open cluster NGC 752.

NGC 752 is an open cluster in the Andromeda constellation. An object that may have been NGC 752 was described by Giovanni Batista Hodierna before 1654. It was independently discovered by Caroline Herschel in 1783 and cataloged by her brother William in 1786. NGC 752 is at a distance of 1,300 light-years away from the Solar System.[1]

Upsilon Andromedae (υ Andromedae / υ And) is a binary star located approximately 44 light-years away from Earth in the constellation Andromeda. The primary star ( A) is a yellow-white dwarf star that is somewhat younger than the Sun. The second star in the system (Upsilon Andromedae B) is a red dwarf located in a wide orbit.

As of 2008, three confirmed extrasolar planets are known in orbit around the primary star. All three are likely to be Jovian planets that are comparable to Jupiter. Upsilon Andromedae was both the first multiple-planet to be discovered around a main sequence star, and the first multiple- planet system known in a multiple star system.

Upsilon Andromedae A is a yellow-white dwarf of spectral type F8V, similar to our Sun but rather younger, more massive, and luminous. According to its entry in the Geneva-Copenhagen survey, the star is around 3.1 thousand million years old, and has a similar proportion of iron relative to hydrogen to the Sun.[4] At around 1.3 solar , it will have a shorter lifetime than our Sun. The amount of ultraviolet radiation received by any planets in the star's habitable zone would be similar to the ultraviolet flux the Earth receives from the Sun.[5]

Upsilon Andromedae B is a red dwarf of spectral type M4.5V located at a distance (in the plane of the sky) of 750 AU from the primary star. The true separation between the two stars is unknown because the displacement along the line of sight between us and the Upsilon Andromedae stars is unknown, so this value is a minimum separation. It was discovered in 2002 in data collected as part of the Two Micron All Sky Survey.[6] The star is less massive and far less luminous than our Sun.

The Washington Double Star Catalog lists two optical components, however these do not share the system's proper motion and only appear close to Upsilon Andromedae because they happen to lie near the same line of sight.[7]

[EDIT] PLANETARY SYSTEM

The innermost planet of the Upsilon Andromedae system was discovered in 1996 and announced in January 1997, together with the planet of Tau Boötis and the innermost planet of 55 Cancri.[8] The discovery was made by and R. Paul Butler, both astronomers at San Francisco State University. The planet, designated Upsilon Andromedae b, was discovered by measuring changes in the star's induced by the planet's gravity. Because of its closeness to the parent star, it induced a large wobble which was detected relatively easily. The planet appears to be responsible for enhanced activity in the of its star.[9]

Even when this planet was taken into account, there still remained significant residuals in the radial velocity measurements, and it was suggested there might be a second planet in orbit. a three-planet model best fit the data.[10] The two outer planets were designated and in order of increasing distance from the star. Both of the two outer planets are in more eccentric orbits than any of the planets in our solar system (including Pluto).[11] The outermost planet resides in the system's habitable zone.[5]

Upsilon Andromedae c gradually oscillates between circular and eccentric states every 6,700 years. The existence of further planets too small or distant to detect has not been ruled out, though the presence of Jupiter-mass planets as close as 5 AU from Upsilon Andromedae A would make the system unstable.[16] planet M jupiter Period (days) discovered B 0.69 4.62 1996 C 1.92 241 1999 d 4.13 1278 1999