Looking back: The Sky at Night
5 April 1978
On the 5 April 1978 episode of
The Sky at Night, Patrick
Moore talked with astronomer George
Taylor from the
Royal Greenwich Observatory. Since 1952, Taylor had been working on a new method to measure the size of asteroids using occultations.
An occultation occurs when a foreground star passes in front of a background one, temporarily blocking out its light. By measuring the length of time the star blinks out, astronomers can gauge the size of the asteroid passing in front of it.
Taylor was able to compute the times when occultations were likely to occur for the planets and 80 of the largest asteroids. When a potential occultation was due, he would pass the news to observatories who would pin down the orbits of the asteroid more precisely to determine if an occultation would happen. During the occultation itself, astronomers would measure how long the star disappeared for. Using at least two measurements from different locations, Taylor could work out the size of the passing asteroid. Measuring occultations has become a popular project for many amateur astronomers. With enough people working together at disparate locations, it’s possible to map out the rough shape of the asteroid’s shadow as well.