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Дата изменения: Tue Oct 2 12:20:27 2012 Дата индексирования: Sun Feb 3 16:39:39 2013 Кодировка: Поисковые слова: rosat |
A reconfigured camera can take wide-field exposures of astronomical objects (constellations, the Milky Way, zodiacal light, moving artificial satellites, meteor showers, variable stars, etc.) to reveal much fainter objects and structures than seen by naked eye. Such pictures can be "still" frames to record, for example, the circular motions of stars due to the Earth's rotation, or "tracked" frames in which the camera is mounted in a simple tracking device which follows the moving stars to keep objects in focus.
One type of tracking device is called a "barndoor tracker." It is conceptually simple and very rewarding to build. In the process, students will apply the concepts of celestial north and sidereal motions, utilize simple geometry or trigonometry, and learn about elementary woodworking. Many undergraduate students in McCarthy's college astronomy class have chosen to build barndoor trackers for astrophotography projects with their "One-Time Use" cameras; similar projects are certainly open to high-school students, as well.
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Figure
3. The constellation Orion setting in the western sky north
of Tucson, Arizona. KODAK 800 speed IMAX film was used for this 25-minute,
untracked exposure. The colors of the stars are clearly revealed in
the photo, yet not in this black & white image, indicating their relative
temperatures. The streaking is caused by the Earth's rotation during
the exposure and can be used to show that all celestial objects appear
to move around the celestial poles during a 24-hour period. Students
can frame their photographs to include both celestial and local objects
in a creative combination. Photo courtesy of the authors.
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Figure
4. The constellation Orion imaged with a disposable camera
mounted on a barndoor tracker. This 15-minute exposure from Steward
Observatory on Kitt Peak, southwest of Tucson, Arizona, reveals stars
as faint as 7th magnitude, about 2.5 times fainter than the human eye
can see. The Orion nebula, M42, is apparent in the "sword" of Orion
and is a location where new hot stars are being born. Photo courtesy
of the authors. |
Your pictures can be developed at quality photo-finishing stores. We recommend removing the film canister and taking it directly to the store. Instruct the developers to "print for black" or "print for stars" so they know the pictures will contain a black background with small faint points of light (i.e., the stars). Otherwise, they may not see any recognizable objects and elect not to print any of your pictures. Also, ask them "not to cut the negatives" so they won't cut your picture in half by mistake. Be sure to inspect the negatives yourself using a small magnifier. You may find pictures the developer should have printed. Ask for the canister to be returned with your pictures.
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Figure
5. The "flash" of an Iridium satellite as it reflects sunlight towards
Tucson while moving rapidly around Earth. This untracked picture is
a 7-minute exposure taken in evening twilight. The visual magnitude
of the satellite was -7. If you know your latitude and longitude, you
can use the following website to predict the times, locations, and brightnesses
of the Iridium satellites: www.heavens-above.com.
Photo courtesy of the authors. |
SUSAN KERN and DON MCCARTHY have been doing research and educational activities together for several years at The University of Arizona in Tucson. Susan receives her undergraduate degree in astronomy, physics, and religious studies this year and promptly heads to MIT where she is enrolled in the graduate program in Planetary Sciences. Don is an infrared astronomer specializing in instruments and techniques which remove the effects of atmospheric blurring. Using the Hubble Space Telescope at infrared wavelengths, Susan and Don have recently discovered an apparent impact feature on the icy surface of one of the Solar System's most distant objects, 1995 GO. Susan and Don can be reached via email at susank@as.arizona.edu and dmccarthy@as.arizona.edu, respectively.
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