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On Thu, 23 Jun 2005 01:30:25 +0100, Tim Auton wrote:
> "Algomeysa2" <Algomeysa2NOSPAM@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
>>I saw a bit today where they said that the Deep Impact, the space probe
>>hitting comet Tempel, might be visible through binoculars.
>>
>>It's supposed to hit at 1:52am Eastern Standard Time July 4th. If my
>>Starry Night program has the comet in the right place, it's so close to the
>>horizon in the West that it'd be impossible to see where I'm at
>>(Southeastern United States).
>>
>>Still I had to wonder.... when they say 1:52am EST, is that the real
>>impact time? If so, since the comet is a little under one A.U. away, I
>>guess it'd be closer to 1:59am-2:00am when it'd be visible through
>>binoculars. But by that time, the comet would be under the horizon (from
>>my vantage point).
>
> Not only do we have to consider the light-time, but also the time the
> debris cloud will take to reach its maximum extent. Will it happen in
> a few seconds, effectively an explosion, or will a significant
> proportion of the debris be gaseous emissions from the heat generated
> by the impact? I could see the latter taking several minutes, perhaps
> more, to reach its maximum extent.
>
> I presume we don't know exactly or we wouldn't be doing the
> experiment, but does anybody have any good info on the expected
> timescale of the brightening and subsequent dimming?
>
>
> Tim
No one really knows since this hasn't been done before. One well-known
comet expert I spoke to last week says that if anything is visible it will
probably be best seen two or three days after the impact. It will take
time for the material to spread out in the tail and catch the maximum
amount of sunlight it can reflect. It's a good bet that the impact itself
won't cause enough brightening to be visible (i.e., a bright spot on the
nucleus from the impact that can be seen from Earth) but the increase in
the material a day or two or three later might be. But, again, no one
really knows.
The experiment isn't just to see what happens with the visibility of the
tail, though. There will be a spectrograph watching to see what the
material is and many types of broadband imaging will be done. The imaging
effort has been going on for many months already to characterize what is
"normal" for the comet including its outbursts as it approaches perihelion.
As for the event being visible in binoculars, I think that's very doubtful
primarily because the comet itself cannot be seen in binoculars. It's
presently a difficult object in a large amateur telescope (a friend reports
it being difficult in a 17.5" f/4.5 from the Grand Canyon). The amount of
brightening has been predicted as anything up to five magnitudes but that
would be spread out over a large area in the tail. That might bring it to
binocular visibility but that's not "the event" as in seeing something
happen when the probe impacts as the news piece is implying.
Mike Simmons
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