Astronomy 10: Astrophotography

Astrophotography: Star Trails

Worth 20 points -- Due Monday, June 17th 2002

Star trails like the ones shown in class are easy to photograph. Simply set your camera on a tripod (or, if you don't have a tripod, secure it to a rock, fence post, etc.). Then point up, make the lens open wide (that is, set it to a low f-number, like f/2.8), disable the flash unit, set the camera focus to infinity, and open the shutter for some period of time (preferably with a cable release to minimize vibrations). Be careful not to shine lights near the camera while the shutter is open. Your camera must have the option of taking a long exposure (normally the "bulb" setting of cameras); an "instamatic camera" won't work, and even some automatic single-lens-reflex (SLR) cameras don't have this option. Your best bet is a manual SLR.

The point of this lab is to obtain trailed photographs of the stars. This will

  1. give you a sense of the rotation of the celestial sphere (i.e., the rotation of Earth)
  2. allow you to photograph and learn some constellations
  3. appreciate the different colors of stars
  4. perhaps catch some meteor ("shooting stars") on film if you are lucky.
Take at least 3 photographs of the sky with ISO 100 color print film. If you are using faster film from a bright location, you should use a higher f-number (like f/4 or f/5.6) to cut out some of the light. Use different exposure durations for each photograph, with a minimum duration of 4-minutes. We want to see star trails due to Earth's rotation, so the exposures shouldn't be too short. For example, from a bright site like Berkeley you could use 4, 8, and 12-minute exposures. Longer exposure times will give you longer star trails and will improve your chances of catching a meteor (or an airplane), but exposure times shouldn't be too long if your location suffers from light pollution. For best results in a bright location, point your camera toward bright stars. Most pleasing photos can be obtained from a dark location, away from city lights: you can then use faster film (e.g., ISO 400) and longer exposure times (perhaps 10, 20, and 30 minutes).

Be sure to record the following:

Bring a notepad and a small flashlight for this purpose. The flashlight will also allow you to examine your camera settings.

Take your roll of film to a photo store to have it developed and printed. You may use slide film if you prefer; just enclose the slides in an envelope and attach it to your lab write-up. Label each slide properly. Turn in your three best photos having different exposure durations, and write a report (about 3 pages, double-spaced) describing and interpreting what you have recorded. If you think you have captured an airplane, meteor, or artificial satellite discuss which you think it is and why?

You may photograph the sky with your friends, but each of you must turn in different photographs and your own descriptions.

IMPORTANT NOTE: When taking astrophotos, it's best to take one normal (daylight) photo at the beginning of the roll, and if possible one at the end as well. You can also use a flash photo or a nearby object, but of course a flash photo of the sky will yield nothing. The reason for doing this is that the photo lab will need one normal frame to determine the starting point of your negatives; otherwise they might accidentally cut them in the wrong places!

For more details on astrophotography see the following links:

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