Aloha Mr. Palmer and Mr. Bock Below is the article, which is presented for publication for the Hawaii Tribune-Herald in Na Kilo Hoku o Mauna Kea On January 3,2003 Thanks David A. Byrne, Manager, Mauna Kea Visitor Information Station The Universe Tonight Presents An introduction talk on digital imaging at CFHT By Dr. Jean-Charles Cuillandre Canada-France-Hawaii Telescope The January presentation of the popular “The Universe Tonight” program will be presented at the Mauna Kea Visitor Information Station off Saddle Road. The Mauna Kea Program will be held on Saturday January 4,2003 at the Onizuka Center for International Astronomy, located at the 9,300-foot level of Mauna Kea. The presentation will begin at 6p.m. and stargazing with portable astronomical telescopes will follow after sunset. Dr. Jean-Charles Cuillandre of Canada-France-Hawaii Telescope presents an introduction talk on digital imaging at CFHT. The Visitor Information Station can be reached from Hilo, Waimea and Kona via Saddle Road. Seating is limited and will be provided on a first-come first-serve basis. The Universe Tonight is presented the first Saturday of each month at the Visitor Information Station. A special speaker from a different Mauna Kea observatory shares recent observations and discoveries with the general public. For more information on programs at the Mauna Kea Visitor Information Station visit the Web site www.ifa.hawaii.edu/info/vis or call (808) 961-2180. Two Astronomical Data Revolutions Eugene Magnier, CFHT / IfA There is a romantic and widespread misconception about astronomers: when we observe at a telescope, we put our eye behind an eyepiece and squint through the telescope to study the stars and galaxies.  Alas, this vision of the astronomer at work has been out of date for several decades.  Instrumentation has replace the human senses in astronomy to such an extent that most major observatories built in the past two decades or more do not even have the optics needed to let a person gaze through the telescope.  Astronomy is a science that depends on precise measurements of the positions of objects seen in the telescope and of their brightness.  As a result, analytical measuring tools have long since supplanted the notoriously unreliable human eye. At first, starting in the late 1800s, the use of photographic film and glass plates replaced visual observations.  Not only is possible to assure the positions of stars in a photograph (even a ruler can be used), the photographic film can be exposed for many hours at a time. Unlike the eye, which refreshes itself roughly ten times per second, the longer the photographic film is exposed, the more light it accumulates, allowing fainter and fainter objects to be detected. Photography was a major advance over visual observations, and remained the main method of data collection in astronomy for roughly a century. However, photography has several serious limitations.  First, film is relatively insensitive, detecting only about 5 percent of the available light.  Photographic plates also have a limited sensitivity range: if the star is too bright, the negative turns to solid black; too faint and nothing is recorded.  Finally, photographic plates are not a digital format: to analyze the images with a computer it is necessary to scan the plates, a technology which has only recently become widely available.  For these reasons, starting in the 1970s, astronomers turned to electronic imagers, particularly CCDs. CCDs, charge-coupled devices, are the basis of modern consumer digital cameras.  Astronomers started to use CCDs at most observatories in mid-1980s.  These devices began a data revolution in astronomy comparable to the introduction of film a century before.  CCDs have nearly perfect sensitivity, detecting up to 80 percent of the light, or more.  Suddenly the small 1m-class professional telescopes had the sensitivity equivalent to 10m telescopes with plates.  CCDs also have a wide sensitivity range allowing the observation of faint objects near very bright objects.  Also, CCDs are directly readout into a computer allowing astronomers to perform sophisticated image analysis to extract the most information from the images.  CCDs have one major drawback compared to film: limited size.  The early generations of CCDs were only a fraction of an inch on size, compared with typically 6 to 8 inches for photographic plates.  More area for the detector means a larger portion of the sky can be studied in one image, resulting in more objects.  These early detectors had 0.25 megapixels, compared with the consumer cameras now available with 4 or 6 megapixels.  Over the decade from the mid 1980s to the mid 1990s, astronomers worked vigorously with chip design experts to develop larger and larger detectors.  By the mid-1990s, the detectors had reached a natural limit of about 8 - 9 megapixels, with a length of about 3 inches.  Beyond this size, manufacturing errors result in too many failed devices. Astronomers changed tactics to increase the imaging area of the cameras within a reasonable price: CCD mosaics.  In this technique, the camera uses a collection of 4, 8, 12, or more detectors placed very close together to fill out a larger area.  CCDs were developed for this technique in which all of the readout wires were located on one of the four edges, allowing the imaging area of one CCD to nearly touch the imaging area of its neighbor on three sides.  The Canada-France-Hawaii Telescope (CFHT) is one of the leaders in this area, and is in the process of converting from a 12 CCD mosaic called CFH12K, with 100 megapixels, to a 40 CCD mosaic called MegaCam, with 360 megapixels. These large cameras allow astronomers to observe many stars at once: a technique that is crucial for finding the rarest objects.  Recent projects at CFHT which have depended on large-scale imaging studies have included: distant supernova searches to measure the expansion of the Universe and the presence of 'dark-energy'; searches for brown-dwarfs, objects which not quite massive enough to be stars; measurements of the subtle distortion of the shapes of distant galaxies caused by the presence of dark matter in the Universe; searches for Kuiper belt objects, large comet-like bodies in our Solar System, beyond the orbit of Neptune.  These wide-field imagers continuing to extend our understanding of the Universe, even as they challenge astronomers to handle the very large quantities of data they produce. Not only do these cameras provide invaluable data to the astronomers, they can also be used to produce stunning images of the sky.  However, to produce pretty images requires a surprisingly large effort.  At the Universe Tonight, CFHT Astronomer Jean-Charles Cuilllandre will demonstrate some of the techniques needed to handle the images from the large CCD mosaic cameras and to create beautiful imagery.