[AZ-Observing] Re: Weekend Observing
- From: Jeff Hopkins <phxjeff@xxxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Mon, 27 Feb 2006 14:14:06 -0700
Thanks Brian,
The infrared is certainly interesting. I'll try the multiple stars
techniques next change i get. Looks like the next few days will be
cloudy, even some possible rain.
Jeff
At 13:41 -0700 2/27/06, Brian Skiff wrote:
>>> Are you following a star
>>> from the meridian down to higher airmass?
>
>>> Yes!
>
> OK, your negative extinction then almost certainly results from
>the transparency changing during the interval. Since the airmass
>associated from the trough Thursday/Friday was receding during
>Friday evening, there's good reason to think this is what was
>going on. At J and H, you'll be affected more directly by water-vapor
>changes as well as just plain clouds because of the way the
>atmospheric 'windows' at these wavelengths change shape as a function
>of, say, precipitable water-vapor.
> Instead of following just one star from high to low (or the
>reverse), you can avoid the temporal changes in extinction by
>measuring several stars in as short a time as possible at both
>high and low airmass. If you get negative extinction from this
>procedure, then it's simply cloudy. Presumably you have some list
>of bright JHK standard stars you can use for doing the extinction.
> ...it occurs to me that the patchy nature of extinction at the
>near-IR wavelengths may cause it to come out with a negative value
>even if it's "clear" in the usual meaning of this term. This might
>be a good question to ask on the AAVSO photometry discussion list,
>for instance.
>
>\Brian
--
Jeff Hopkins
HPO SOFT
http://www.hposoft.com/Astro/astro.html
Hopkins Phoenix Observatory
7812 West Clayton Drive
Phoenix, Arizona 85033-2439 U.S.A.
www.hposoft.com
--
See message header for info on list archives or unsubscribing, and please
send personal replies to the author, not the list.
Other related posts:
