I think there is a greater probability of a dobsonian telescope catching fire than starting a forest fire, which would really hurt the wallet. My telescope manuel says that the UTA can catch fire if pointed at the sun. I always use caution when collimating the scope in the daytime. Debbie
[Original Message] From: Wayne Reese <waynereese@qwest.net> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Date: 9/30/2004 2:20:55 PM Subject: RE: [Utah-astronomy] Re: Starpartyetiquetteforcrumbcrunchersandparents
I bought an F-4 canopy from Smith and Edwards last year to build a flight simulator for my Grandkids. They (Smith and Edwards) said that they would have had a larger selection, but the Sun shinning though one canopy started a fire in their yard. I know this isn't telescope related, it does demonstrate a sun caused accidental fire.
Wayne
Ps as long as I'm using band space, Dale Hooper, it looks like I moving to 359 N 1000 E, Hyde Park, anywhere near you?
-----Original Message----- From: utah-astronomy-bounces+waynereese=qwest.net@mailman.xmission.com [mailto:utah-astronomy-bounces+waynereese=qwest.net@mailman.xmission.com ] On Behalf Of Brent Watson Sent: Wednesday, September 29, 2004 10:36 AM To: Utah Astronomy Subject: RE: [Utah-astronomy] Re: Starpartyetiquetteforcrumbcrunchersandparents
Starting a fire is just as unlikely off axis as well. The light cone doesn't change much off axis, and most folks don't park their scopes within a focal length of tinder. If they did they wouldn't have much of the sky visible. You must also have a fast enog=ugh scope to start the fire. The focal ratio required to do this is much smaller than most scopes. You really have to try to do any damage. The reticle in a Telrad doesn't catch fire, it just melts - a much lower temperature is required to melt mylar than to burn something up.
There is a tale that one of the ancients started the sails of his oponents ships on fire by stationing his troups around the bay with individual mirrors, and then having them focus their mirrors on the sails. It has been shown that this too is very improbable.
Brent --- Chuck Hards <chuckhards@yahoo.com> wrote:
Lisa, read my last post. Yes, you CAN start a fire with a telescope mirror, it's just unlikely on-axis unless tinder is very near the focal plane.
Eyepieces left on a chart table can do the trick, too, and tell all those folks with melted Telrad reticles that the sun isn't a problem.
I would like to see John's calculations, assumptions.
I have several large mirrors and am happy to demonstrate the off-axis danger on a sunny day.
--- John and Lisa Zeigler <john@johnstelescopes.com> wrote:
Ya, John did the physics of it for me last night and figured out exactly what diameter mirror at what focal length you would need to start a fire. Let me tell you, it aint going to happen! Sometimes its difficult living with an over analyzer. I just meant it figuratively.
Lisa Zeigler www.johnstelescopes.com www.mirrorkits.com
-----Original Message----- From: Brent Watson [mailto:brentjwatson@yahoo.com]
Sent: Wednesday, September 29, 2004 7:52 AM To: Utah Astronomy Subject: RE: [Utah-astronomy] Re: Star partyetiquetteforcrumbcrunchersandparents
The forest is no more at risk from a alrge scope than from a small scope. It is pretty hard to get enough energy out of a scope and across a distance large enough to do any damage. The image, and the energy in the image, spread out very quickly and become a non-problem.
Brent
--- John and Lisa Zeigler <john@johnstelescopes.com> wrote:
We have a 1/4" plywood shield over our mirror on the truss tube Dob. It sits about an inch over the mirror on three screws from the mirror cell. This protects it from wind, rain, dust, and the forest from harm.
Lisa Zeigler www.johnstelescopes.com www.mirrorkits.com
-----Original Message----- From: Debbie [mailto:astrodeb@earthlink.net] Sent: Tuesday, September 28, 2004 1:17 PM To: Utah Astronomy; Utah Astronomy Subject: RE: [Utah-astronomy] Re: Star party etiquetteforcrumbcrunchersandparents
That is another reason I don't like to leave my scope up during the daytime, besides animals getting to it. A big dobsonian could cause a forest fire or blind someone.
Debbie
[Original Message] From: Patrick Wiggins <paw@trilobyte.net> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Date: 9/28/2004 11:10:18 AM Subject: [Utah-astronomy] Re: Star party etiquette forcrumbcrunchersandparents
I seem to remember many years back a star party up by Kamas where Brent's monster scope ended up catching a frisbee or two. But then I seem to also remember that later in the day the scope became a chimney
when sunlight found its way to the primary mirror and smoke was seen emanating from the tube...
Patrick
Chuck Hards wrote:
Don't be so sure; I've seen many telescopes
(present company
excepted, of course) that may as well have been trash-cans...
--- John and Lisa Zeigler <john@johnstelescopes.com> > > Solid tube Newtonian telescopes, no matter how > much they look like > > trash cans or basket ball hoops are not for > throwing things into..
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