Re: Question on visibility of orbit changes

Tony Beresford (
Sat, 14 Feb 1998 23:37:41 +1000

At 09:37 14/02/98 +0100, Mark Borg wrote:
To amplify on Phil Chien's remarks on several points in
reverse chronological order.
1. Quite a few people saw the exhaust/blowdon cloud from the
    Centaur that launched Cassini. That evening the local astro
    Society was doing a school visit, and 20-30 people saw it.
    As detailed in this list I was alaerted by a member of the
    public and caught the last remnants of the cloud in binoculars.
    That very active observer
    Gordon Garrad of Loomberah NSW, imaged the cloud, Centaur
    and Cassini. Images on his Web page
2. The Moonwatch team based in Townsville Queensland saw Apollo 11
    achieve Translunar injection in July 1969. I beleive it is mentioned
    in The Moonwatch Newsletter of July/August of that year. Harvard
    University library probably has archive of the above newsletter.
In general what one sees is not the exhaust itself, but some result
of an interaction with the environment, which may just be flourescence
caused by the ultraviolet (or shorter ) parts of sunlight, or a
reaction between the exhaust molecules and the local ones.
The well known comet seeker Bill Bradfield observed the injection
of a military satellite into geostationary orbit, one evening
at the conclusion of an evenings comet hunting. With a solid fuel
rocket burning large amounts of aluminium, the exhaust has a large
component of aluminium oxide particles, which reflect sunlight nicely
The gradually expanding patch was visible for half an hour.
Tony Beresford