Tuesday, August 31, 2004

Fred L. Whipple

A great man died yesterday at the grand old age of 97. Fred Lawrence Whipple was born in 1906. He joined the Harvard College Observatory (now the Smithsonian Astrophysical Observatory) and in the early 1930s, he became interested in meteors, working on determining the orbits of meteors, using multiple station photography using cameras outfited with a rotating shutter. Using parallax to measure the spacial location of a meteor imaged by two cameras several miles apart, and by measuring the rate of motion of the meteor by measuring the distance traveled between shutter interruptions in the trail, he was able to determine the location and velocity of meteors and thereby, their orbits. Prior to his work, other observers had found that a large number of meteors they had observed resulted in hyperbolic solar orbits. Whipple even modeled an extra-solar origin for some of these hyperbolic meteors. However, Whipple found that he needed to accurately time the appearance of the meteor for the orbit he got varied considerably from hyperbolic to elliptical depending on when during the long exposure that he assumed the meteor had appeared. Once he accurately timed the appearance of a number of meteors, he found that none of them were hyperbolic!

Whipple became interested in the physics of meteoroid ablation and atmospheric drag. This work led to a study of cometary nuclei which ultimately led to his revolutionary and still widely accepted "Icy Conglomerate" model of the comets nucleus - the so called "dirty snowball". His landmark paper in 1950 along with a paper by Jan Oort on the distribution of orbits of the long period comets in the same year completely changed our view of the comet complex and of the origin and evolution of the solar system.

Whipple had the foresight prior to the 1957 launch of Sputnik to set up a network of cameras that ultimately were used to track the first manmade Earth orbiting satellites. In 1972, "The Collected Contributions of Fred L. Whipple", a two volume collection of all of Whipples publications up to that point was published. These two volumes are each nearly 1000 pages long and are still an important collection, more than 70 years after the first of Whipples publications.

I have fond memories of meeting with Fred Whipple in about 1995. We chatted for perhaps an hour and he happily autographed my copy of the first volume of his Collected Contributions and also gave me an autographed stamp from the Republique Islamique de Mauritanie which honors him. We also talked at length about some of my work on comet photometry. We will miss Fred L. Whipple.


Monday, August 30, 2004


Doomsday is not upon us.....

Asteroid (4179) Toutatis will be making a very close approach to Earth in September. Toutatis is a Near-Earth Asteroid discovered in 1989 by Christian Pollas at Caussols in France on plates obtained by Alain Maury and Derral Mulholland. On September 29 of this year, it will pass just 1.550 million kilometers (963,000 miles) away from Earth - that's just 4 times the distance to the Moon - a close approach, but not an impact. Here's a couple websites which summarizes what we know about Toutatis:






Of course, there are some rumors of doomsday with claims that this asteroid is going to actually hit Earth instead of fly harmlessly past. Here's a sample of webpages about those rumors:





If Toutatis were to hit Earth, and it might someday (but don't worry, it won't anytime in the predictable future - at least a few hundred years...), it would do a great deal of damage. The object is about 2.4 by 4.6 kilometers in diameter. It would cause a crater around 40 kilometers in diameter (the size of a medium to large city) and throw enough debris into the atmosphere to likely cause a small nuclear winter type event or at least affect the climate on Earth for a few years. It would devistate an area the size of a state and if it impacted in an ocean, it would cause tsunami along the shores of that ocean. But humananity would survive the impact - Toutatis is not large enough to cause a mass extinction event, though it would kill a great many if it were to hit.

In any case, Toutatis poses no immediate danger despite the cries of a few kooks and crackpots who claim otherwise..... On the other hand, this close approach gives a wonderful opportunity for those with small telescopes to see an asteroid visually. I had the opportunity to view an asteroid I discovered in 1991 when I spent an evening using a 16 inch telescope. I was prepared with finding charts of the area the asteroid would be passing through. It was moving about an arcsecond every couple seconds and was about 12th magnitude. As we centered up the telescope on the field, my eye was drawn to one star in particular - it wasn't moving fast enough to be obviously moving, but it would shift enough to be obvious compared to the stars around it after a few moments and the subtle motion was enough for my eye and brain to pick it out. Toutatis will be about 9th magnitude at its brightest as it zips across the sky. At its brightest it will be best viewed from the southern hemisphere, but before that when it's brighter than 12th magnitude, it will be visible to anyone with a telescope and some advanced preparation.