This feature is inspired by the questions we have received over the years from interested readers. If you have a question about an astronomical topic, please forward it to us.

The following are excerpts from correspondence between Dr. Jon Giorgini of the Jet Propulsion Laboratory and MIRA's Dr. Whitney Shane. Dr. Giorgini, who with others recently published work on asteroid (minor planet) 1950 DA, originally wrote to Edith Wirtanen, the widow of the asteroid's discoverer, C. A. Wirtanen, inquiring about the circumstances of the discovery at Lick Observatory. Mrs. Wirtanen, a member of the Friends of MIRA, asked Dr. Shane, whose father was director of the observatory at the time of the discovery, to respond.

Jon Giorgini: An asteroid designated 1950 DA, first discovered by [C. A. Wirtanen] in February of 1950, was recently rediscovered, having been lost for the last half century. … subsequent work can be summarized by saying that 1950 DA has some chance of impacting the Earth 880 years from now, on March 16, 2880. The issue is interesting because the impact probability is 1000 times larger than for any other case, and the asteroid is of a size (1.1 km) so as to have global consequences if it did impact. … I write in search of historical context for the discovery of 1950 DA.

Whitney Shane: I should begin by writing something about the nature of the astronomical project that led to the discovery of 1950 DA. The 20-inch astrograph of the Lick Observatory [was used to measure] the motions of stars with respect to distant galaxies. [The first photographic plates] formed the basis of the Lick galaxy counts as published by [C. D.] Shane and Wirtanen. In addition, C.A. Wirtanen carefully scanned each plate directly after the observation in search of comets and interesting minor planets. He found a considerable number of comets and more minor planets than could possibly be followed with the facilities available. … there were often dozens of them … [so] he took note only of those with unusual motions [such as] fast-moving objects … close to the Earth and of particular interest ... because they could be used to determine the scale of the Solar System in absolute units. 1950 DA was one of these fast-moving objects.

At the time … interest in minor planets was at a minimum, and nowhere was it less than at the Lick Observatory. Thus the amount of time spent following up these objects was very limited.

JG: Was the discovery of 1950 DA the subject of news articles at the time?

WS: To the best of our recollection, this discovery did not receive any particular publicity outside the normal astronomical channels.

JG: … was it known (based on the few measurements available) that the asteroid was making an approach to Earth in March of 1950?

WS: … the length of the trail on the discovery plate would already have indicated that this was a near-Earth asteroid, and this would certainly have been confirmed by whatever preliminary orbit was calculated … The possibility of a collision was certainly never considered, and the time was far too short to set up an observing campaign for scale determination, as outlined above.

JG: The movie When Worlds Collide went into production in 1950 and was released in 1951. In it, references are made to a computer named "DA" and to "celestial objects passing by the Earth." Neither reference is in the original 1932 novel. Since Paramount owned the rights to the novel for 17 years, I wonder why … they chose to make it in 1950 [and] if news of the discovery of 1950 DA and its close approach to the Earth … could have been the inspiration to finally put the movie into production. Did [Wirtanen] have any contact with the producer … or the screenplay author … or the film's technical advisor Chesley Bonestell regarding the matter?

WS: I am sure that if anyone involved in making a film with such a title [reminiscent of Velikovsky's pseudo-scientific Worlds in Collision] had contacted Mr. Wirtanen or anyone else at Lick, it would have caused an amount of teasing and general hilarity that neither Mrs. Wirtanen nor I would easily have forgotten. However, the two coincidences that you mention do certainly suggest a connection. It seems quite plausible that some alert person, upon reading a news item about 1950 DA, might have thought of the old novel … In that case, he was way ahead of the astronomers, who were not thinking in those terms at all.

 

 Fall 2002 Contents   Newsletter Index   Mira Home Page 

Last updated 12/15/02 DMC