Image of the day

Captured by
Douglas Rollain

M20 Trifid Nebula in LRGBHa

About Astromart

My Account

New to Astromart?

Register an account...

Need Help?

Posts Made By: Alan French

March 26, 2010 02:47 PM Forum: Equipment Talk

Best Year's For Cave Astrola's Mirrors And Scope's

Posted By Alan French
I purchased an 8" f/8 mirror from Cave in 1965 and it was superb. It really spoiled me.

Clear skies, Alan

March 28, 2010 09:28 PM Forum: Global Warming - REAL or NOT

And No Bougie Man, Either

Posted By Alan French
A shame they did it when there was a bright gibbous Moon in the sky.

April 10, 2010 01:48 AM Forum: Reflectors

dew on primary...help

Posted By Alan French
Daniel White said:

I have an 8" f6 metal tube reflector, and on very cold nights I get moisture on the primary. Has anyone successfully used a dew-zapper or like product on a reflector?

This is a problem with metal tubed reflectors. Most paints are good radiators and the metal is a good conductor. The tube cools below ambient temperature and then the primary mirror can also get below ambient and dew over. My wife's 6" f/8 Edmund frequently had the secondary dew up, and on some nights even the primary got dew. I solved the problem by removing the paint (bare aluminum does not radiate well) and lining the tube with cork. The cork alone would probably do the trick.

Clear skies, Alan

June 9, 2010 11:49 PM Forum: Global Warming - REAL or NOT

Legal verdict: AGW Science a Sham

Posted By Alan French
Why is there so much misleading press here? Legal verdict, to me, implies a trial, which was certainly not the case here.

Maybe we should start taking our science courses from lawyers.




June 10, 2010 06:46 PM Forum: Birding Optics and Photos

Young Red-breasted Nuthatches

Posted By Alan French
Another shot.

June 12, 2010 02:32 PM Forum: Global Warming - REAL or NOT

AGW Mysteries Explained

Posted By Alan French
A great post that quite clearly shows you just don't get it.

Clear skies, Alan

June 20, 2010 02:06 PM Forum: Refractors

science behind focus of light

Posted By Alan French
When an object is infinitely far away - virtually anything in the night sky qualifies - the light rays can be pictured as parallel. When an object it close, the light rays coming from it are diverging, and the focal plane moves farther away from the lens or mirror. The closer the object is to the telescope, the more the incoming light rays diverge, and the farther back the focal plane moves.

It's easier to envision if you think of a point source of light moving closer to the telescope.

Clear skies, Alan

June 20, 2010 02:23 PM Forum: Refractors

science behind focus of light

Posted By Alan French
You might find this helpful...
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/lenseq.html

Clear skies, Alan

July 1, 2010 01:14 AM Forum: Global Warming - REAL or NOT

CO2 Causes Cooling

Posted By Alan French
Tell that to the Venusians.

Clear skies, Alan

July 24, 2010 02:10 PM Forum: Solar System Observing

Oh Boy! Mars as big as the full moon time again!

Posted By Alan French
At least when this now gets forwarded to me by my friends they add "Here we go again!"

I note that on August 27 this year Mars will almost by on the opposite side of the Sun from us, at a distance of just under 319 million kilometers, and appearing only 4.4 arc seconds in diameter.

Clear skies, Alan


Funding Member

Sponsors


View all sponsors

Search