ASP: Making Your Own Astronomical Camera

Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.astrosociety.org/edu/publications/tnl/50/camera3.html
Äàòà èçìåíåíèÿ: Tue Oct 2 12:20:27 2012
Äàòà èíäåêñèðîâàíèÿ: Sun Feb 3 16:39:39 2013
Êîäèðîâêà:
Ïîèñêîâûå ñëîâà: trifid nebula

The Universe in the Classroom

Making Your Own Astronomical Camera

Turning the Camera Skyward

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.

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.

Figure 3 shows a still frame of the constellation Orion setting in the western sky. This image was obtained in a 25-minute exposure. In Figure 4, Orion was tracked in a 15-minute exposure. This picture reveals objects more than 2.5 times fainter than can be seen by the naked eye, including not only stars but also the Orion nebula (M42), where new stars are being born. Figure 5 shows the "flash" of reflected sunlight from an orbiting Iridium communications satellite. All these pictures used KODAK 800 Max color film. We have also succeeded with KODAK 400 NC color portrait film which can be purchased more economically in a bulk roll (100 feet).

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.

To obtain your own night-time pictures, begin by finding the darkest possible site away from neighborhood or city lights. Position the camera away from any wind on a stable platform to avoid vibration. Before you begin, the film must be initialized: advance the film by pushing the shutter button, and rotate the advance wheel until you can see or feel the button depress and pop back. Then advance the wheel a little more until it resists further motion. Turning the wheel may require more force than a normal camera, so be prepared to use a small coin or screwdriver for assistance. The counter mechanism no longer operates so you must keep a record of your pictures and the number of remaining exposures. After your last picture, the advance wheel will become very difficult to turn because you will be pulling directly against the tape used to fasten the film to the spool.

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.

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.

You can be very creative with your astronomical camera. In addition to taking pretty pictures of celestial and local objects, you can search for trails from moving objects (meteors, satellites, airplanes), and look for variable stars, such as the eclipsing binary Algol in Perseus. You can even use your camera to measure the effects of light pollution around your neighborhood by determining the magnitudes of the faintest stars in exposures of the same length. For more information about light pollution, see the website of the International Dark-Sky Association.

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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