Twinkle, Twinkle, Little Asteroid

Stars twinkle, but usually not like this! On the morning
of Nov. 20, asteroid 752 Sulamitis will be seen, from some
places on Earth, passing in front of a star in the
constellation Gemini, making the star fade away for up to 10
seconds. This will be long enough for amateur astronomers
with home video cameras to contribute valuable information to
studies on the size and shape of the asteroid.

Not much is known right now about 752 Sulamitis, except
that it may be up to 105 kilometers (65 miles) in diameter.
The path of this stellar eclipse may cut across the upper
eastern half of the United States. “Being able to see an
asteroid pass in front of, or occult, a star is rare,” said
Lance Benner, an expert on asteroids at NASA’s Jet Propulsion
Laboratory, Pasadena, Calif., and a member of the
International Occultation Timing Association (IOTA).

This is the first time an asteroid occulting a star can
be seen in North America since 1975, when such predictions
became readily available. The star, known as Tejat, is bright
enough to be seen with the naked eye. The asteroid is very
faint — about 18,000 times fainter than the star, and cannot
be seen without a telescope.

The region where the eclipse is visible will be a narrow
band slanting from North Carolina’s coast northwest to
Madison, Wis., to northern Alaska. Residents of Chicago,
Minneapolis, Indianapolis and Cincinnati may also be able to
see the asteroid as it fades out for about two seconds.

The star, which is located in the southern corner in the
constellation Gemini (just above Orion), will be intersected
by the asteroid from 6:41 to 6:49 a.m. Eastern time. It will
take eight minutes to move from the East Coast to the north
boundary of the continental United States. Star-watchers can
set up their cameras and telescopes, mark their location, and
tune in to short-wave radio station WWV, Boulder, Colo. at
2.5, 5, 10, 15, 20 megahertz. By coordinating with the
station’s time signal, observers can mark when they see the
star, which will be just one-third of the moon’s brightness,
disappear and reappear as the asteroid blocks it from view.
The occultation will be unlike the normal twinkling of the
star caused by Earth’s atmosphere, because it will take about
three seconds to fade out, remain obscured from view for 10
seconds and fade back in 3 seconds.

Observations of the shadow across the star can be
reported to the International Occultation Timing Association.
An analysis of the observations will help define the
asteroid’s shape and size. Reports from those who observe the
star but don’t see it disappear are still scientifically
useful — they can help determine the size of the asteroid and
the precise location of the asteroid’s track across the United
States. And observers in outlying areas may see only a partial
eclipse of the red supergiant star, since it doesn’t have a
sharp outline like younger stars.

Observations can be reported to the IOTA, online at
http://www.lunar-occultations.com/iota/iotandx.htm. JPL is
managed by the California Institute of Technology for NASA.
For more information, and a partial map of viewing locations,
see www.jpl.nasa.gov.