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Re: AW: [APML] Tenerife skies (was: Exposure times with IDAS filter)
Well, in my opoinion the Europeans are pretty nationalistic and hate to admit
that skies round about places other than near Europe are better than in Eurpe. I
had much fun with this with the Swiss. They have the World Radiation Center and
they were always taughting clarity of air above high mountain observatoories in
Switzerland and at places like Davos. I used to tell them to get real and do the
experiments from the American Mauna Loa Observatory, whch has enourmously clear
skies, but it had a problem: it was American!
In fact, probably the skies above Tenerife are OK. The transparency might be
down a little, but what's more important is that there are few interfering
sources of light pollution and light scattering. Usually nearby light messes up
astrophotography more than sky transparency.
best regards,
glenn shaw
Bert Katzung wrote:
> Hi Glenn:
> That's very interesting! Now that we know about Gobi desert dust making
> western US skies less transparent (when they're not completely occluded by
> clouds!), I guess we'll have to start paying more attention to dust as yet
> another form of pollution. If the Sahara dust is a year-round thing, it's
> surprising that any European countries are still investing in professional
> scopes on the Canaries, etc.
> 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 5:40 PM
> Subject: Re: AW: [APML] Tenerife skies (was: Exposure times with IDAS
> filter)
>
> 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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