jrasc june 1998 final - The Royal Astronomical Society of Canada

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jrasc june 1998 final - The Royal Astronomical Society of Canada

News NotesEn ManchettesCANADIANS FLOCK TO CARIBBEAN FOR ECLIPSEBalmy temperatures combined with the promise of a solar eclipsemade the Caribbean region a magnet for Canadian amateurastronomers in late February. The maximum partial eclipse didnot exceed 30% as seen from anywhere in Canada, and despiteEl Niño, February weather held little appeal. Caribbean islands,particularly Aruba and Curaçao in the Netherlands Antilles,were crowded with eclipse viewers, and several cruise ships hadeclipse themes with Canadian tour directors or experts. Tortuousair routings meant that western Canadians had travel times aslong as sixteen hours to the viewing destinations, with arrivaland departure in the wee hours, however, the intrepid travellersto the Caribbean were rewarded with almost cloud-free skies,and totality approaching four minutes. The days before theeclipse, in Aruba and Curaçao, featured generally clear skies andsteady Trade Winds, coming from the east at 20 to 30 km h -1 .By chance, the events of pre-Lenten Carnival were also in progressseveral days before the eclipse, adding to the interest of a tropicalstay. Those attempting to do night-time observing and seesouthern sky objects were generally disappointed in the skyconditions, with severe light pollution made worse by highhumidity. The islands are too small to allow simply driving awayfrom light sources, each being about the size of metropolitanToronto. The need to also find shelter from the wind, if a steadytelescopic view was desired, made overall observing conditionsless desirable than might have been expected. For casual observing,however, many Canadians found staring at Orion directly overhead,while doing the back float in a warm pool, a novel experience.Pre-eclipse weather conditions heightened the tensionleading to the event on February 26. Unlike the preceding days,that of the eclipse was generally cloudy. Disturbances in theregion arise locally, and then are carried downwind, forminglong streamers of heavy cloud. The phenomenon was particularlytroublesome for land-based observers, while cruise ships couldmaneuver to find generally clear conditions, according tometeorologist Alister Ling, who was on board the NorwegianSea. Some of the disturbances brought heavy, although brief,rain to the windward slopes, along with great anxiety for observerslocated there. In the face of cloudy conditions, some did makea last-minute dash to the generally clearer leeward side of theislands. Those who stood their ground were relieved as a clearingtrend set in after first contact, and the total phase could be wellseen through very thin cloud. Some western Canadians rememberedthe 1979 eclipse, also on a February 26, and found warm viewingconditions more agreeable than those on the central plains!That, and the stunning spectacle of the Caribbean eclipse,convinced many that Europe will be the place to be on August11, 1999. So many, in fact, that the NASA Goddard Space FlightCenter has needed to reprint its guide for that event. Page 106of the 1998 Observer’s Handbook gives more details of theupcoming eclipse and how to access the online version of thedetailed eclipse guide.BROADENING THE VIEWThe new electronic imaging technology of charge-coupled devices(CCDs) has brought about a revolution in astronomical photographyboth for research and recreational use. The many advantagesinclude a high sensitivity, particularly in the red and near-infraredareas of the spectrum, linear response allowing multi-dayexposures such as the Hubble Deep Field, the convenience of anon-chemical imaging process, and having digital data withmany advantages over analogue photographs. It is not oftenrealized by those who do not actually use CCDs that they havethe drawback of very limited physical size, which permits onlya very narrow field of view. For example, the Wide Field/PlanetaryCamera 2 on the Hubble Space Telescope has an angular viewof about 2.5 arcminutes width, and even that has a part missing.That angle is less than one-tenth the apparent diameter of theMoon! Hubble would not be considered a very large telescopeif found in a ground-based observatory, and CCDs similar tothose used in its camera would produce an even narrower viewif used in a much larger telescope.In the past, making a detector with a larger field of viewwas mainly a matter of making a larger photographic emulsion,but making CCDs larger is not so easy. They are fabricated onsilicon wafers and making large and defect-free wafers is difficult.The best approach is to use several CCDs arranged together inthe image plane of the telescope. Such an approach is beingtaken at the Canada-France-Hawaii Telescope (CFHT) now,with ambitious plans for the future development of a “Megacam”imaging a very large field. A camera with 8192 by 8192 pixels iscurrently in use, soon to be joined by the CFH12k camera, whichboosts one of these dimensions to 12288. The resulting imagearea is similar to that of a 4 by 6-inch photograph, with 15-micron resolution throughout. As a mosaic of 12 CCDs, such animage would have small seam marks throughout. Nevertheless,a much more efficient use of large telescope time can be madewith this much of the image plane covered. The 8k and 12kcameras will lead up to Megacam, with an image roughly 250mm on a side, corresponding to a one degree field of view (over500 times the angular area of Hubble’s WFPC). Such a large areawill require modification of the CFHT optical system, and poses108JRASC June/juin 1998

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