Re: AW: [APML] Tenerife skies (was: Exposure times with IDAS filter)

[Glenn Shaw <gshaw@alaska.net>]

Bert:

I conducted an experiment in Kenya some years ago and did a large amount of
research on dust and meteorology across Africa. Tomarrow I'll check back through
the old records and see if I can get you some information on the seasonality of
dust over Africa. In general, all northern Africa is quite turbid, but some
seasons are worse than others. I have a standing argument with European
colleagues, who want to brag up the skys in N. Africa. I tell them that in
general, these are pretty turbid skies, but nationalism comes into play and they
disagree.

Someone on this chat list takes photos from nambia and I think that in this part
of Africa, the skies can be good. you have to go south of the intertropical
convergence zone, I think to get good skies in Africa.

glenn shaw

Bert Katzung wrote:

> Hi Glenn:
> Are you saying that the skies are terrible there right now (from Sahara
> dust) and for the forseeable future? In other words, when did you make your
> measurements and how far into the future can you extrapolate? Or is this a
> daily measurement? Ulrich is talking about going in April.
> Thanks....
> Bert
>
> Bert Katzung
> katzung1@attbi.com
> www.astronomy-images.com
>
> ----- Original Message -----
> From: "Glenn Shaw" <gshaw@alaska.net>
> To: <astro-photo@seds.org>
> Sent: Sunday, January 06, 2002 1:59 PM
> Subject: Re: AW: [APML] Exposure times with IDAS filter
>
> Tenerife has pretty terrible skies due to extensive, thick dust blowing from
> the
> Sahara Desert. I made optical depth measuremetns there, finding the optical
> depth at 500 nm wavelength to be between 0.15 and 0.25. You would be much
> better
> off staying completely away from northern Africa and going to the southwest
> US,
> Australia or Hawaiian Islands.
>
> glenn shaw
>
> Ulrich Beinert wrote:
>
> > Matt,
> >
> > thanks for the tips. Even if the skies are not 7m, they'll be way better
> > than anything I've ever had in my life. Europe is a really unfortunate
> place
> > to be if you're an astrophotographer (or doing any form of astronomy for
> > that matter). It's just too crowded here! :-)
> >
> > When you were on Tenerife, were you up on the mountain? How good were the
> > skies? Do you have any pictures from when you were there? There are some
> on
> > this website: http://aida.astroinfo.org/levens/
> >
> > Ulrich
> >
> > -----Ursprüngliche Nachricht-----
> > Von: owner-astro-photo@seds.org [mailto:owner-astro-photo@seds.org]Im
> > Auftrag von Matt BenDaniel
> > Gesendet: Sonntag, 6. Januar 2002 15:29
> > An: astro-photo@seds.org
> > Betreff: Re: [APML] Exposure times with IDAS filter
> >
> > Ulrich,
> >
> > I've been to Tenerife and the skies are definitely not as dark as mag 7.0.
> > One possible problem they have is sometimes they get fine Saharan dust in
> > the air, which can ruin the transparency. I would say don't use the filter
> > if the transparency is good. Also, I would only use the filter for
> emission
> > nebulae. The rule of thumb I use is 1.5x exposure time with the filter.
> >
> > Matt
> >
> > At 11:35 AM 1/6/2002 +0100, Ulrich Beinert wrote:
> > >When using my IDAS filter from my "dark-sky" site, which has a lim. mag.
> of
> > >about 5.5, I can expose twice as long when using the IDAS filter in order
> > to
> > >get the same background brightness.
> > >
> > >In April, I'll be flying to Tenerifa, where the sky will be *very* dark
> at
> > >2200m altitude. Still, I'm thinking of using the filter anyway, because
> > >there will always be *some* light pollution, and I've heard that using
> the
> > >filter at 6.5-7m sites makes sense too. Can I also double the exposure at
> > >such a dark site, or would that cause the background to get too bright?
> > >
> > >Ulrich
> >
> > --
> > Matt BenDaniel
> > http://starmatt.com
> >
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