Calendar of Events PUBLIC OBSERVING Volume 34 Number …physics.ku.edu/sites/physics.drupal.ku.edu/files/...NASA Space Place 4 Planets Easier to Find 5 Cub Scout Event 6 Comet Double-header

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Calendar of Events PUBLIC OBSERVING

Prairie Park Nature Center SUNDAY— December 7

8:00 - 9:30 PM

MONTHLY MEETINGS 3139 Wescoe Hall

7:00 PM FRIDAY—November 21

Cub Scout Public Education

President: Rick Heschmeyer

[email protected] Treasurer:

Dr. Steve Shawl [email protected]

University Advisor: Dr. Bruce Twarog [email protected]

Webmaster: Gary Webber

[email protected] Observing Clubs

Doug Fay [email protected]

Report from the Officers:

Our September Public Observing was another success. The weather cooperated again, the parking lot lights were turned off and we had about 35 people attend and view the night sky through club members' telescopes. Thanks again to all the volun-teers. Our October Club Meeting featured a presentation entitled "Recipe for a Gal-

axy Cluster". Dr. Greg Rud-nick, one of KU's newest as-tronomy faculty, gave a fun and very interesting presenta-tion on a subject that he is obviously passionate about. Dr. Rudnick is a great addition to the KU Astronomy Department. This month's Public Observing will take place at Prairie Park Nature Center on the evening of October 26 at 8 PM. Our November Club Meeting will

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Volume 34 Number 11 November 2008

INSIDE THIS ISSUE

Of Local Interest (continued) 2

New Light on the Sun 3

New Galaxy Clusters 3

NASA Space Place 4

Planets Easier to Find 5

Cub Scout Event 6

Comet Double-header 7

Hottest Planet Found 7

Cosmic Lens Reveals Vio-lence

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Antikythera Revisited 9

Of Local Interest—Hubble Status Report #6—10/23/08

The Hubble Space Telescope Science Instrument Control and Data Handling sys-tem was reactivated on Thursday, October 23. This should enable Wide Field Planetary Camera-2 science observations to resume on Saturday, October 25. The Advanced Camera for Surveys Solar Blind Channel science observations should resume later next week. Additional background: The Independent Review Team, chaired by Wallops Flight Facility director John Campbell, and the Hubble Program reported their assessment to Goddard management yesterday. The review team primarily studied the sudden halt of the NASA Standard Spacecraft Computer-1 which occurred on October 16, along with the apparent failure during turn-on of the planetary camera’s low voltage power supply earlier that same day. The team concluded that a hardware problem did not occur on the camera. The anomaly was because of a limit-checking algorithm that triggered before the data that it was checking was valid. A commanding change on the instrument will elimi-nate this condition and both teams expect a nominal low voltage power supply turn-on when it is commanded on next week. Regarding the sudden halt of the spacecraft computer, the team concluded that three separate events occurring with near-simultaneity were responses to a single triggering event. The triggering event was most likely caused by a self-clearing short-circuit, or a transient open-circuit, in the Science Instrument Control and Data Handling system. One or more such events would not be highly improbable in hard-ware inactive since 1990, and will not harm the telescope, although it could cause

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About the Astronomy Associates of Lawrence The club is open to all people interested in sharing their love for astronomy. Monthly meetings are typically on the second Friday of each month and often feature guest speakers, presentations by club members, and a chance to exchange ama-teur astronomy tips. Approximately the last Sunday of each month we have an open house on Memorial Stadium. Periodic star parties are scheduled as well. For more information, please contact the club officers:Luis Vargas at [email protected], Gary Webber at [email protected], our faculty advisor, Prof. Bruce Twarog at [email protected]. our events coordinator,

Rick Heschmeyer at [email protected]. Because of the flexibility of the schedule due to holidays and alternate events, it is always best to check the Web site for the exact Fridays and Sundays when events are scheduled. The information about

AAL can be found at http://www.ku.edu/~aal.

Copies of the Celestial Mechanic can also be found on the web at http://www.ku.edu/~aal/celestialmechanic

be our annual Cub Scout Astronomy Belt Loop presentation, which this year will be held in Wescoe Hall instead of Malott. Since we couple an observing session with the Cub Scout event, there will not be a separate Public Observing ses-sion in November. If you can assist by helping out with either the October Public Observing or the November Cub Scout As-tronomy event (or both), please contact Rick Heschmeyer. I've had a couple of members communicate that they have tele-scopes but don't really know how to use them well enough to bring to the Public Observing sessions. Nonsense! Bring your scope out to Prairie Park and we will show you how to use it! The only bad telescopes are those that don't get used! I look forward to seeing everyone, and their telescopes, at our upcoming events.

Please contact Rick Heschmeyer if you are planning on attending, with or without scope. Agan, mark your calendars for Fri-day, November 21 at 7 pm. That is the date for our annual Cub Scout Astronomy program. Last year we had 275 atten-dees, so we’ll need as much help as we can get for this event.

If anyone has any ideas, suggestions, or input on how we can make the club better, please contact Rick. Look forward to seeing everyone at the October Open House and/or the November meeting.

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another interruption of science operations. Based on these latest findings, Goddard Center management and NASA HQ concurred with the Hubble team’s plan to power on the spacecraft computer and then monitor it for about 24-hours to as-sess its operations.

THE ABOVE WAS AN UPDATE to the FOLLOWING STORY

If NASA had kept to its original schedule, astronauts would have made their fifth and final mission to service the Hubble Space Telescope back in August. It's a good thing they didn't. The space agency announced that an onboard communication problem has temporarily shut down the World's Greatest Telescope — and postponed the planned house call in orbit, scheduled to begin October 14th, until no earlier than next February or perhaps April. The failure occurred in the Command Unit Science Data Formatter, an electronics package that moves digitized streams of data from the science instruments to spacecraft's digital tape recorder for later playback to Earth. The CU/SDF has worked great for 18 years, so faulty craftsmanship isn't the issue. Nor is the venerable space observatory in any real trouble. The good news is the that Hubble's designers included a second unit for redundancy. As far as engineers know, it still works — but it hasn't been checked since before HST's launch more than 18 years ago. Changing from one to the other is entirely doable but a lot more involved than just throwing a switch from "A" to "B". So Hubble's handlers are dusting off the owner's manual to begin the process; that might be completed by early next week, at which point the observatory will come back online. More weighty, for the moment, is whether replacing the defective unit should be added to the already jam-packed "to do" list for astronauts on the forthcoming servicing mission, STS 125. A spare CU/SDF does exist at NASA's Goddard Space Flight Center (which manages Hubble's science payload) and could be made flight-ready soon. During a hastily convened briefing for reporters, Preston Burch, Hubble manager at NASA-Goddard, noted that replacing the 136-pound unit, which is roughly the size of a two-drawer filing cabinet, should be "a relatively straightforward activity" that would add only about 2 hours to one of the mission's five planned spacewalks.

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Satellite Data Sheds New Light On The Sun Press release from Science

Some of the first data collected by the CoRoT space telescope mission, launched in December 2006, provides valu-able information about the physical vibrations and surface characteristics of nearby stars that are similar to our Sun, researchers say. This novel information illustrates the great value of space-based observations, and provides astrono-

mers with insights into the interior of our Sun, other stars, and the overall evolution of our galaxy.

The related report was published by the journal Science on Friday, 24 October, and featured on the cover. Sci-ence is the journal of AAAS, the nonprofit science society.

Dr. Eric Michel from the Observatory of Paris-LESIA-CNRS and a large group of colleagues from across Europe and South America analyzed the data from the CoRoT satellite to determine that three nearby stars, all significantly hotter than the Sun, also have larger vibra-tions, or oscillations, and much finer surface texture, or granulation. With this unprecedented data, the research-ers show that the stars' oscillations are about 1.5 times as vigorous as the Sun's, and their granulation is about three times finer. The observed oscillations, though much more intense than the Sun's, are still about 25% weaker than most models predicted.

These landmark results represent the first time research-ers have been able to accurately gauge the oscillation amplitudes and granulation signatures of solar bodies in our universe, other than the Sun. The initial discovery of oscillations in our Sun in the late 1970's led to the crea-tion of "solar seismology," which has since been used to measure the movement and transport of heat around the Sun. Solar seismology led to rapid progress in under-standing the Sun's internal structure, but eventually re-searchers hit a wall. Accurate measurements of solar-like oscillations require the collection of precise data from

long, uninterrupted sequences of observations, making ground-based study impossible.

"Although the energy from the Sun is more or less constant over our lifetimes, even very small variability in its output can have important effects," says Brooks Hanson, deputy editor for physical sciences at Science Magazine. "Understanding that small variability is critical, for example, in predicting solar storms and space weather, and for re-solving the causes of changes in Earth's climate… These observations [by Michel and colleagues], and more in the future, will provide the essential data for improving our understanding of the interior of the Sun, and stars in general."

The findings presented by Michel and colleagues are based on light curves obtained with the CoRoT satellite over a period of 60 days, and help to refine our understanding of stars and the Sun. These results "allow us to place our Sun within the bigger picture of the evolution of our galaxy and the local universe," says Ian Osborne, senior editor of Sci-

Illustration of a stellar global oscillation shaking the whole star interior and thus carrying information on it. Yellow refers to maximum temperature variations due to oscilla-tions. (Credit: Image courtesy of Aarhus University/S. Frandsen)

New Galaxy Clusters Are Detected United Press International

A U.S.-led international team of scientists has detected long wavelength radio emissions from a colliding, massive galaxy cluster. The discovery, which scientists say is not duplicated at shorter wavelengths usually seen in such objects, implies existing radio telescopes have missed a large population of such colliding objects. The researchers said their finding provides an important confirmation of the theoretical prediction that colliding galaxy clusters accelerate electrons and other particles to very high energies through the process of turbulent waves. "This result is just the tip of the iceberg," said Professor Greg Taylor of the University of New Mexico. "When an emerging suite of much more powerful low fre-quency telescopes, including the Long Wavelength Array in New Mexico, turn their views to the cosmos, the sky will 'light up' with hundreds or even thousands of colliding galaxy clusters." The research that included scientists from Italy's Insti-tute of Radioastronomy, the University of Bologna, the Smithsonian Astrophysical Observatory, the National Radio As-tronomy Observatory, and the Naval Research Laboratory appeared in the Oct. 16 issue of the journal Nature.

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The Chemical Weather Report

“Sunny tomorrow with highs in the mid-70s. There’s going to be some carbon monoxide blowing in from forest fires, and all that sunshine is predicted to bring a surge in ground-level ozone by afternoon. Old and young people and anyone with lung conditions are advised to stay indoors between 3 and 5 p.m.”

Whoever heard of a weather report like that?

Get used to it. Weather reports of the future are going to tell you a lot more about the atmosphere than just how warm and rainy it is. In the same way that satellite observations of Earth revolutionized basic weather forecasting in the 1970s and 80s, satellite tracking of air pollution is about to revolutionize the forecasting of air quality. Such forecasts could help people plan around high levels of ground-level ozone—a dangerous lung irritant—just as they now plan around bad storms. “The phrase that people have used is chemical weather forecasting,” says Kevin Bowman of NASA’s Jet Propulsion Laboratory. Bowman is a senior member of the technical staff for the Tropospheric Emission Spectrometer, one of four scientific sensors on NASA’s Aura satellite.

Aura and other NASA satellites track pollution in the same way that astronomers know the chemical composition of stars and distant planetary atmospheres: using spectrometry. By breaking the light from a planet or star into its spectrum of colors, scien-tists can read off the atmosphere’s gases by looking at the “fingerprint” of wavelengths absorbed or emitted by those chemicals. From Earth orbit, pollution-watching satellites use this trick to measure trace gases such as carbon monoxide, nitrogen oxide, and ozone. However, as Bowman explains, “Polar sun-synchronous satellites such as Aura are limited at best to two overpasses per day.” A recent report by the National Research Council recommends putting a pollution-watching satellite into geosynchronous orbit—a special very high-altitude orbit above the equator in which satellites make only one orbit per day, thus seeming to hover over the same spot on the equator below. There, this new satellite, called GEOCAPE (Geostationary Coastal and Air Pollution Events), would give scientists a continuous eye in the sky, allowing them to predict daily pollution levels just as meteorologists predict storms. “NASA is beginning to investigate what it would take to build an instrument like this,” Bowman says. Such a

chemical weather satellite could be in orbit as soon as 2013, accord-ing to the NRC report. Weather forecasts might never be the same.

Learn more about the Tropo-spheric Emission

Spec-

trometer at tes.jpl.nasa.gov. Kids can learn some elementary smog chemistry while making “Gummy Greenhouse Gases” out of gumdrops at spaceplace.nasa.gov/en/kids/tes/gumdrops. This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

Example of visualization of data from the Tropospheric Emission Spectrometer. These frames are from an animation that steps through transects of the atmosphere profiling vertical ozone and carbon monoxide concentrations, combin-ing all tracks of the Aura satellite during a given two week period.

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Earth-like Planets May Be Easier To Find Than Previously Thought: Young Planets Stay Hotter Longer

MIT Press Release Hot, young planets may be easier to spot because they stay that way longer than astronomers have thought, according to new work by MIT planetary scientist Linda Elkins-Tanton.

For a few million years after their initial formation, planets like Earth may maintain a hot surface of molten rock that would glow brightly enough to make them stand out as they orbit neighboring stars. Elkins-Tanton, Mitsui Career Development Professor of Geology in the Department of Earth, Atmospheric and Planetary Sciences, says the "magma ocean" stage for Earth-sized planets may last a few million years, much longer than previously estimated. "That means we may actually see them elsewhere, as detection systems get better," she said.

Elkins-Tanton presented her new findings this week at the annual meeting of the American Astronomical Soci-ety's Division for Planetary Sciences, being held this year in Ithaca, N.Y. The research shows that even after the surface magma solidifies, within about five million years, it could stay hot enough to glow brightly in infrared light for tens of millions of years, providing a relatively long window for detectability.

The big problem for astronomers hoping to detect planets around other stars is the vast difference in brightness between the star and the planet, which shines only by reflecting light from its parent star. But the difference in brightness in infrared wavelengths for a glowing, molten planetary surface would be much less, making the detec-tion more feasible.

The long duration of the molten stage turns out to be the result of a two-stage process, Elkins-Tanton explained. The initial heating, generated by a combination of radioactivity in the planet's interior and the heat generated by the collision of millions of chunks of rock crashing together to form the planet, actually is quite short-lived: The planet's surface is expected to solidify quickly, within a few hundred thousand years, as originally thought. But then a secondary upheaval begins, in which heavier iron-rich material that has solidified at the surface begins to sink toward the core, causing other hotter material to rise to the surface.

This "overturn" process, it turns out, produces the much-longer-lived molten surface, lasting for millions of years, she said. Because the Earth's crust is so dynamic, there is no material left from that initial epoch that could be studied to test this modelling, she said, but on other planets such as Mars or Mercury there might be early rem-nant rocks that could be tested. The analysis also leads to specific conclusions about the surface composition of planets, so detection of certain specific minerals on Mercury, for example, which the MESSENGER spacecraft may be able to carry out when it begins its study of the planet in 2011, might support the theory.

In addition, the detection of hot, young planets around other stars, which might become possible over the next several years, might provide another line of evidence to support this conclusion, she said.

It'll take a few months to certify that the spare is flightworthy, but NASA officials seem willing to accept that delay. This means the Space Shuttle Atlantis, already on the launch pad at the Kennedy Space Center in Florida, will be rolled back into its shelter. So will a second shuttle, Endeavour, that's standing by just in case a dramatic rescue of the Hubble repair team had been necessary. The STS-125 crew hopes to install two scientific instruments (the Cosmic Origins Spectrograph and a replacement Advanced Camera for Surveys), repair a third, and swap in new batteries, gyroscopes, and other components. The spacewalkers will also attach a mechanism to allow the docking of a rocket stage at some future date for Hubble's safe disposal. Should the replacement data formatter prove unfit to fly (considered unlikely), the repair mission will be hustled back to the launch pad as soon as it can — probably in November. "Hubble has a habit of coming back from adversity," notes Edward Weiler, who heads NASA's Science Mission Di-rectorate. "This particular failure was anticipated 20 years ago, and we have spare hardware ready to go."

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A comet doubleheader By Ron Cowen, Science News

The first contact binary is discovered — a comet that is two chunks somehow held together

When Comet 8P/Tuttle passed close to Earth early this year, astronomers took its portrait with the Arecibo radio tele-scope in Puerto Rico. To their surprise, the radar images have revealed that the comet consists of two chunks that appear to be held together by a narrow neck of material. The portrait suggests that the body is the first known example of a comet that is a contact binary. Researchers aren’t sure how the structure formed.

John Harmon of Arecibo Observatory reported the findings on October 11 in Ithaca, N.Y., at the annual meeting of the American Astronomical Society’s Division for Planetary Sciences.

Collisions that might form a binary are much more common among the rocky bodies in the asteroid belt than in the much more remote and sparsely populated regions of the solar system where comets originate.

“To make a [comet] contact binary implies a formation mechanism that we don’t understand, but we’re guessing would be different than that in the asteroid belt,” says study collaborator Mike Nolan of Arecibo. It’s possible, he says, that 8P/Tuttle broke into pieces sometime in the past when it neared the sun — the comet make its closest approach every 13.5 years — and its surface warmed.

Such fragmenting is well known among comets, but in this case some of the pieces, which travel on similar but not identical orbits, would have had to reassemble. “Our understanding of how you make comets must now include the possibility of making an object” like 8P/Tuttle, says Nolan.

Observations using the Hubble Space Telescope and the Spitzer Space Telescope show that one the comet’s chunks is 5.6 kilometers in diameter and the other is 2.4 kilometers in diameter, Philippe Lamy and Olivier Groussin of the As-trophysics Laboratory in Marseilles, France, reported.

Hottest Planet Ever Discovered By Clara Moskowitz, Space.com

In the hunt for extrasolar planets, a new find is shattering records left and right.

A planet called WASP-12b is the hottest planet ever discovered (about 4,000 degrees Fahrenheit, or 2,200 degrees Cel-sius), and orbits its star faster and closer in than any other known world This sizzling monster whips its way around its parent star about once a day (for comparison, the fastest circling planet in the solar system, Mercury, orbits the sun once every 88 days). To make such swift progress, the planet circles extremely close-in to its star — about 2 percent of the distance from the Earth to the sun, in fact, or 2 million miles (3.4 million kilometers).

"WASP-12b is incredibly interesting, because we're at a stage in the study of exoplanets where we're finding new exam-ples all the time," said Don Pollacco of Queen's University in Northern Ireland, who is a project scientist for the Super-WASP (Super Wide Angle Search for Planets) project that discovered WASp-12b. "It was exciting because it was the shortest period and the hottest planet, but I suspect there are even shorter period planets, and hotter planets to come."

WASP-12b is a gaseous planet, about 1.5 times the mass of Jupiter, and almost twice the size. The planet, which orbits a star 870 light years from Earth, is especially notable because it pushes the bounds of how close planets can ever come to their stars without being destroyed.

"There is a limit because as a planet gets closer to its star, the radiation field gets more and more intense, and at some point that whole planet will be evaporated by its star," Pollacco told SPACE.com. "Before, some people thought it was impossible to find planets that had 1-day periods. I think it's so early in the whole subject, and it takes a number of objects before you can start setting limits."

The planet is also so hot that its temperature matches that of some stars. This planet, however, is definitely not a star because its mass isn't nearly large enough for the internal thermonuclear reactions that define stars. WASP-12b is one of only about 50 extrasolar planets that have been detected through the transit method, meaning they were found by meas-uring the dip in brightness of their parent star as they pass in front of it and block part of its light.

"It's an incredibly hard way to detect planets, because the size of this dip when it moves across the star is very small," Pollacco said. "These objects are difficulty to find, but they're incredibly valuable when you do find them because they tell you so much."

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Cosmic Lens Reveals Distant Galactic Violence Science Daily

By cleverly unraveling the workings of a natural cosmic lens, astronomers have gained a rare glimpse of the violent as-sembly of a young galaxy in the early Universe. Their new picture suggests that the galaxy has collided with another,

feeding a supermassive black hole and triggering a tremendous burst of star formation.

The astronomers used the National Science Foundation's Very Large Array (VLA) radio telescope to look at a galaxy more than 12 billion light-years from Earth, seen as it was when the Universe was only about 15 percent of its current age. Between this galaxy and Earth lies another distant galaxy, so perfectly aligned along the line of sight that its gravity bends the light and radio waves from the farther object into a circle, or "Einstein Ring."

This gravitational lens made it possible for the scientists to learn details of the young, distant galaxy that would have been unobtainable otherwise.

"Nature provided us with a magnifying glass to peer into the workings of a nascent galaxy, providing an exciting look at the violent, messy process of building galaxies in the early history of the Universe," said Dominik Riechers, who led this project at the Max Planck Institute for Astronomy in Germany and now is a Hubble Fellow at the California Institute of Technology (Caltech).

The new picture of the distant galaxy, dubbed PSS J2322+1944, shows a massive reservoir of gas, 16,000 light-years in diameter, that contains the raw material for building new stars. A super-massive black hole is voraciously eating material, and new stars are being born at the rate of nearly 700 Suns per year. By comparison, our Milky Way Galaxy produces the equivalent of about 3-4 Suns per year. The black hole appears to be near the edge, rather than at the center, of the giant gas reservoir, indi-cating, the astronomers say, that the galaxy has merged with another.

"This whole picture, of massive galaxies and supermassive black holes assembling themselves through major galaxy mergers so early in the Universe, is a new paradigm in galaxy formation. This gravitationally lensed system allows us to see this process in unprecedented detail," said Chris Carilli, of the National Radio Astronomy Observatory.

In 2003, astronomers studied PSS J2322+1944, finding the Einstein Ring by observing radio waves emitted by mole-cules of Carbon Monoxide (CO). When astronomers see large amounts of CO gas in a galaxy, they conclude that there also is a large amount of molecular Hydrogen present, and thus a large reservoir of fuel for star formation. In the latest study, scientists painstakingly produced a physical model of the lensing intermediate galaxy. By knowing the mass, structure and orientation of this galaxy, they could then deduce the details of how it bends the light and radio waves from the more-distant galaxy. This allowed them to reconstruct a picture of the distant object. By doing this with multiple VLA images made at different radio frequencies, they were able to measure the motions of the gas in the distant galaxy.

"The lensing galaxy was, in effect, part of our telescope. By projecting backward through the lens, we determined the structure and dynamics of the galaxy behind it," said Fabian Walter of the Max-Planck Institute for Astronomy in Ger-many.

PSS J2322+1944 was first discovered by George Djorgovski of Caltech, using the digitized Palomar Observatory Sky Survey. Later radio and optical studies showed that it had a huge reservoir of dust and molecular gas, and indicated gravitational lensing.

Gravitational lenses were predicted, based on Albert Einstein's General Theory of Relativity, in 1919. Einstein himself showed in 1936 that a perfectly-aligned gravitational lens would produce a circular image, but felt that the chances of actually observing such an object were nearly zero. The first gravitational lens was discovered in 1979, and the first Ein-stein Ring was discovered by researchers using the VLA in 1987.

Riechers, Carilli, and Walter worked with Brendon Brewer and Geraint Lewis of the University of Sydney in Australia, Frank Bertoldi of the University of Bonn in Germany, and Pierre Cox of the Institute of Millimeter Radio Astronomy in France.

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Complex clock combines calendars (Followup to Dr. Anthony-Twarog’s Talk Last Year)

Philip Ball, Nature News The Antikythera Mechanism, a clockwork device made in Greece around 150–100 BC, astounded the world two years ago when scientists deduced how this machine was used to make complex astronomical time-reckonings. Now they

say that the instrument, discovered in 1901 in a Mediterranean shipwreck, did much more than that.

Researchers have been trying to decode the mechanism's inscriptions and functions for several years. Their latest findings reveal that it links the technical calendars used by astronomers to the everyday calendars that regulated an-cient Greek society — most strikingly, the calendar that set the timing of the Olympic Games. “The mechanism is full of surprises,” says Alexander Jones of the Institute for the Study of the Ancient World in New York, who is one of the decoding team. “The latest revelations establish its cultural origin for the first time.” The Olympic Games marked the beginning of a four-year timespan called an Olympiad: a calendar system shared by all the Greek city-states, bringing some uniformity to the chronology of the Hellenistic world. The Games began on the full Moon closest to the summer solstice, which meant that calculating the timing required expertise in astronomy. The Olympic Games were the most prestigious of four sets of games in ancient Greece, called the Panhellenic Games. First recorded in 776 BC, the ancient Olympic Games continued until they were extinguished by a ban from the Chris-tian Roman emperor Theodosius I in around 394 AD.

The latest decoding of the Antikythera Mechanism, by British mathematician Tony Freeth of the film company Images First in London and his colleagues, casts fresh light on the way these calendar schemes were planned, used and inte-grated. The device had intermeshed toothed wheels that represent calendar cycles. By turning the wheels, a user could figure out the relationships between astronomical cycles to deduce the relative positions of the Sun and Moon and forecast eclipses. But after two millennia under the sea off the island of Antikythera, near Crete, all that remains of the device are 82 fragments of flaking bronze, including parts of 30 gear-wheels. The numbers of gear teeth are cru-cial, but must be inferred from the partial wheels that remain. And most of the inscriptions are hidden under corrosion and surface accretions. To read them, the researchers used a method called microfocus X-ray computed tomography, which provides X-ray images of slices through the sample, revealing inscriptions buried beneath the mechanism's surface. In 2006, Freeth was part of a team that used this and other techniques to figure out much of the mechanism's func-tion, showing it to be an instrument of unparalleled sophistication in antiquity, more or less unrivalled until the clock-work mechanisms of the later Middle Ages.

Now they say that the device was even more sophisticated than that — it unites abstruse astronomical determinations of time with the calendar of civic society. Another ancient Greek calendar cycle, called the Metonic cycle, was estab-lished to cope with the incommensurability of the lunar cycle and the solar year — the period of Earth's rotation around the Sun, as determined, say, by the time between successive summer solstices. One Metonic period is equal to 235 lunar months, which is almost exactly 19 solar years. The Metonic cycle, thought previously to be used only by astronomers, is represented on a dial on the Antikythera Mechanism. But this dial now turns out to be inscribed with the names of months in a regional calendar used in Corinthian colonies in northwest Greece — providing evidence that the device was used for mundane reckonings, and giving a surprising clue to its origin. As most of the cargo of the Antikythera wreck was from the eastern Mediterranean, researchers had thought that this was where the Mechanism originated too. But Freeth and his team now think that the instrument may have come from Syracuse in Sicily, the Corinthian colony where Archimedes devised a planetarium in the third century BC. “Archimedes died at the siege of Syracuse in 212 BC, so we are confident that he did not make the mechanism,” says Freeth. “But it is possible that it came from a heritage of instrument-making that originated with him in Syracuse. It is an attractive idea, but purely speculative at present.” The Olympiad cycle appears on a subsidiary dial inside the Metonic dial, previously thought to represent an improve-ment on the Metonic cycle called the Callippic cycle. “It really surprised us to discover that it showed the four-year cycle of ancient Greek games”, says Freeth. “The mechanism always produces more surprises.”

See http://tinyurl.com/6f83dt for a video.

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AAL Astronomy Associates of Lawrence

University of Kansas Malott Hall 1251 Wescoe Hall Dr, Room 1082 Lawrence, KS 66045-7582

Celestial Mechanic November 2008