Tuesday, November 17, 2009

What is an Asteroid Occultation ?

 What is an Asteroid Occultation ?

Occultation is a generic astronomical term for a situation where one body "covers" or "passes in front of" another body.  Eclipses and transits are common examples of occultations.  In a solar eclipse, the moon occults (covers) the sun for observers on the earth.  In a lunar eclipse, the earth occults the sun for observers on the moon.  We use the term asteroid occultation for the situation where an asteroid occults a star for observers on the earth. During an asteroid occultation "event" the asteroid momentarily hides the star.  We use the term "asteroid's shadow" to refer to the "shadow" thrown by the asteroid with respect to the light from the occulted star. And the term "shadow path" refers to the path of the asteroid's shadow as it passes across the earth. Depending on the size of the asteroid, its distance from the earth, and its speed in its orbit, the asteroid may cover the star for a fraction of a second or close to a minute.  If the star is relatively bright compared to the asteroid, an observer will see a noticeable drop in magnitude as when the asteroid covers the star.  As asteroids move through the sky they often pass in front of stars from the perspective of an observer on the earth.  However, the vast majority of these occultations involve small asteroids and relatively dim stars, and these events would be very hard to detect with amateur equipment.

No comments:

Post a Comment