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Re: IN SYMPATHY to the Hale-Bopp Cooperative

Article: <5fd5uv$>
From: )
Subject: Re: IN SYMPATHY to the Hale-Bopp Cooperative
Date: 3 Mar 1997 00:28:15 GMT

In article <5fauu7$g4h@news.Hawaii.Edu> David Tholen writes:
>> Give us some statistics, some quoted numbers from the IAU
>> or NASA or JPL, regarding the speculation on Hale-Bopp's
>> size, please do!
> I'm not aware of any size estimates from the IAU or NASA or
> JPL.

How soon we forget! Especially when it all becomes and embarrassment.


Posted on sci.astro by (Ron Baalke)

PR 10/95 25 August 1995
European Southern Observatory
For immediate release


How Impressive Will Comet Hale-Bopp Become in 1997?

A very unusual comet was discovered last month, on its way from the outer reaches of the solar system towards the Sun. Although it is still situated beyond the orbit of Jupiter, it is so bright that it can be observed in even small telescopes. It has been named 'Hale-Bopp' after the discoverers and is already of great interest to cometary astronomers. ... On this basis, Dan Green of the CBAT published a first, highly uncertain parabolic orbit. To some surprise, it showed that the comet was located at a heliocentric distance of no less than 1,000 million kilometres, well beyond the orbit of Jupiter! It was immediately obvious that it must therefore be intrinsically very bright. Indeed, it was about 250 times brighter than Comet Halley when this famous object was observed at the same distance in late 1987!

Why is Comet Hale-Bopp now so bright?

One possible cause for the unusual brightness of Comet Hale-Bopp at its present location, more than 200 million kilometres outside the orbit of Jupiter, is that it possesses a very large nucleus, that is the 'dirty snowball' of dust and ice at the centre of a comet. The larger the diameter of the nucleus, the more sunlight will be reflected from its surface and the brighter will it appear. A corresponding estimate indicates that the diameter of its nucleus would be nearly 100 kilometres, as compared to about 10 kilometres for Comet Halley.


European Southern Observatory
The Enormous Size of Comet Hale-Bopp
30 August 1995

This series of three photos of the unusual Comet Hale-Bopp demonstrates that the comet is much larger than thought so far. In fact, its nucleus is surrounded by a dust cloud that measures more than 2.5 million kilometres across. Note that because of the wide field they represent, each of the images is available in two sizes, the larger of which has considerably better resolution.