Early rising sky watchers can help map the moon's edge with their camcorders. Tomorrow morning, beginning on the East Coast of the United States at about 5:30 a.m., the crescent moon will eclipse the bright star Aldebaran, and astronomers are calling for assistance in recording this rare event. By providing a much more accurate picture of the moon's edge, the resulting images should help astronomers better measure the sun's diameter during solar eclipses.
Occultations--when one celestial body blocks another from our view--happen all the time. But only seldom does the moon cross in front of a star bright enough to be seen beside it, and thus able to provide sufficient light to outline the shape of the moon as it passes the star. By collecting videotapes from locations across the country and then synchronizing the timing of the images they contain, the International Occultation Timing Association (IOTA) will be able to create a picture of the moon's edge, much the way our paired, coordinated eyes create a three-dimensional model of our surroundings. This refined lunar profile can help astronomers better measure variations in solar diameter--a potential factor in climactic cycles on Earth.
To pitch in, you need a camcorder (preferably with a seconds display) and a time base. David Dunham, an astronomer at Johns Hopkins University and president of IOTA, suggests that before recording the occultation, camcorder owners film a TV screen displaying the current time, such as the Weather Channel or CNN, and then keep the camera filming until the occultation is completed and another TV screen with the time is taped. Detailed instructions can be found at IOTA's Web site.