The Universe in the Classroom

Monster Comet Promises Big Show

Astrophotography for Teachers and Students

Herman M. Heyn

Photographing astronomical objects and events is not solely the province of professional astronomers wielding giant telescopes. Many of the beautiful photos in astronomy textbooks were taken by amateur astronomers using everyday camera equipment. With Comet Hale-Bopp fast approaching, now is a perfect time to learn the not-too-difficult science and art of still-camera astrophotography. Nine pieces of equipment are needed:

  1. A 35 mm single lens reflex (SLR) camera is ideal. Its shutter speed control must have a 'B' or 'T' setting for time exposure; the camera must operate mechanically (not by battery) at that setting. The Pentax K-1000 is one such camera.
  2. The best all-around still camera lens has a 50 mm focal length and a speed of f/2 or faster.
  3. A reasonably steady tripod is required. Be sure it can tilt the camera toward the zenith (straight up).
  4. Depressing the shutter button with your finger introduces ruinous vibrations during time exposures. Use a cable release attachment, the type with a locking collar that locks with one hand.
  5. To ensure against jitters as the camera shutter opens and closes, use a piece of black posterboard as the final shutter.
  6. You can count off seconds, but more practical is a timing device. A battery-powered metronome ticking once per second is very handy in the dark.
  7. A dim, red LED flashlight, or a white one with red tissue paper taped over it, will preserve your night vision while reading star maps, camera settings, or notes.
  8. Always keep records of your astrophoto efforts. Data should include date, location, sky conditions, camera and lens specs, film type, and the time, subject, and length of each exposure. A 14-inch clipboard can hold your record sheet.
  9. Last is the 35 mm film. Start with ISO 400 slide film. Slides show exactly what you photographed. Once you know what to expect, you can try print film, as well as faster films. Among the latter are Kodak Gold 1000 and Ektachrome P1600 and Fujicolor Super G Plus 800.

Now that you have the required equipment (see photo), you are ready to take astrophotographs. Pick a site as far as possible from urban light pollution and a night without a bright Moon. Then follow these five steps:

  1. Load the film and snap a daylight scene for reference purposes. Remove any filters, as they can cause internal reflections in night photography.
  2. At the site, mount the camera on the tripod, attach the cable release, set the shutter speed to 'B' or 'T', focus on infinity, and open the lens to its fastest (widest) setting. Organize your timer, clipboard, and red flashlight.
  3. Aim your camera at a constellation and frame it as nicely as you can. Recheck the focus and aperture, and cock the shutter. Start your metronome at one tick per second.
  4. Holding the black posterboard in front of the camera, depress the cable release button to open the shutter, and lock the cable.
  5. On the count of "one thousand zero," move the posterboard away from the camera to begin the exposure. Continue counting: "One thousand one, one thousand two..." At about "one thousand 17" (17 seconds), return the posterboard to the front of the camera and unlock the cable release to close the shutter. Wind the film. Congratulations, you have just taken your first astrophoto!

If your school has a planetarium, you can practice astrophotography in it. Just remember that because the dome is not at infinity, the camera must be refocused for each shot.

In the table below is a list of photogenic evening constellations and recommended exposure times (in seconds) for a 50 mm lens. Note that the farther above or below the celestial equator you point, the longer you can expose before stars leave visible trails. To determine the maximum exposure time without trailing, use the formula: 850/focal length x cosine declination.

Sometimes, star-trailing is desired. The two best constellations for such photos are Orion and Ursa Major. With ISO 400 film and the lens closed to f/4 to avoid overexposing the sky, try a 10-minute exposure. The ultimate, classic star-trails photo is one of an hour or longer centered on Polaris. Close the lens to f/5.6.

Meteors are another possibility. There are about eight "shooting stars" per hour every night, but your chances improve considerably during major meteor showers, such as the Perseids and Geminids. The Perseids peak the evening of Aug. 11 and the Geminids the evening of Dec. 13. Use fast film with the lens wide open. Aim anywhere in the sky and take consecutive 5-minute exposures.

And then there is Hale-Bopp, which, if it lives up to its billing, will be the best comet in decades. From mid-January to mid-March, the comet will be in the predawn sky, and from then until early May, it will be in the post-sunset sky. Use ISO 800 and faster film. With the lens wide open, shoot from 15 to 35 seconds in 5-second increments. For perspective, put trees, buildings, and even people in your foreground.

One last astrophotography suggestion: the near-total lunar eclipse of March 24. With a 50 mm lens, the Moon's image is quite small; a 135 mm or longer focal length is better. Use ISO 200 film and bracket your exposures -- that is, try several camera settings for each stage of the eclipse. While the Moon is full, use 1/400 seconds at f/16, f/11, and f/8. As the shadowed area grows, use progressively wider stops, such as f/11, f/8, and f/5.6. As the umbra enlarges, use f/11, f/8, and f/5.6. At mid-eclipse, when only a sliver of the Moon remains, open to f/4 and bracket from 1/15 to 2 seconds.

Astrophotography is within your reach. Give it a try!

Winter Spring Summer Fall
Orion (17) Leo (18) Hercules (21) Cassiopeia (34)
Taurus-Pleiades (18) Ursa Major (34) Scorpius (19) Triangulum (21)
Canis Major (18) Ursa Minor (50) Sagittarius (20) Andromeda (22)
Perseus (24) Boötes (18) Lyra (21) Cepheus (50)
Auriga (22) Corona Borealis (20) Cygnus (22) Pegasus (18)
Gemini (19) Corvus (18) Delphinus (18) Aries (18)
Cassiopeia (34) Coma Berenices (19) Aquila (17) Double Cluster (30)

HERMAN M. HEYN is a long-time amateur astronomy and astrophotographer living in Baltimore. He is on the staff of the Maryland Space Grant Consortium. Many of his astrophotos have appeared in Sky & Telescope magazine and in astronomy books. Heyn can often be found loitering on street corners in downtown Baltimore at night -- along with his Meade 8-inch Schmidt-Cassegrain telescope, which he encourages passers-by to look through. He welcomes readers' reports on their astrophoto efforts. His mailing address is 721 E. 36th St., Baltimore, Md. 21218; phone: (410) 889-0460.

A Comets Bibliography

Andrew Fraknoi
Foothill College

Comet Hale-Bopp

Books About Comets in General

Articles about Comets in General

Articles About Specific Comets

Comet Observing and Photography

Hale-Bopp on the World Wide Web

http://www.halebopp.com/
http://encke.jpl.nasa.gov/hale_bopp_info.html

ANDREW FRAKNOI is the chair of the astronomy department at Foothill College in Los Alto Hills, Calif. He is the director of the ASP's Project ASTRO and lead author of a new astronomy textbook, Voyages Through the Universe, published by Saunders. He tells us that his son Alex, now 3, knew the words "planet," "star," and "Moon" by age 2.

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