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#11
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Why do you cool a telescope?
Yes, I agree....it seems that image stability (and
resolution) in my scope tends to improve as the night goes on, assuming that the 'seeing' remains relatively constant... I figure about 4-5 hours, with 2 fans running continuously, to stabilize a 30 inch (2" thick) chuck of 110 lb. pyrex. (That's why I get out to our observing site, and get set up, some 2 hours before sunset...allowing lots of time for mirror cool-down)! Clear Skies, Tom W. Chris L Peterson wrote: On Fri, 11 Jul 2003 12:49:54 -0400, bwhiting wrote: Ok, guys, all well and good on deserts...but the original question was...the title above...and I think we all agree that a scope....any scope including refractors, must be brought to, or very close to, the ambient air temperature, to work at maximum efficiency.....just a reminder as to the original question of 'cooling' a scope. :-) Absolutely. However, there are some other interesting related issues. First of all, what is the actual performance difference between a system where the mirror is warmer than ambient and one where it is cooler? I suspect the optical effects are worse in the first case, where convection effects will be more severe. The main equilibrium effect is more likely to do with figure. Because glass is a poor thermal conductor, it will be at different temperatures throughout its volume, and the resulting stress will produce deformation (there are very few truly zero coefficient of expansion mirrors out there.) Too bad aluminum doesn't take a good polish- its thermal properties would make it a good material for mirrors. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#12
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Why do you cool a telescope?
"Paul Schlyter" wrote OK, I've never been there so I you can tell that better than me. But why is the city (town? village?) called Palm Springs? For the same 'reason' we have rivers in Tucson. ;^) (they're all dry riverbeds) Howard Lester (Don't give me this 'dry heat' crap) |
#13
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Why do you cool a telescope?
Hey, you guys are giving Paul a bum-rap....
I've never heard him bad-mouth the USA... You are confusing him with that Kayak-khan-al\mohameed-Maji-Hameed guy... that A-rab who was the terriorist from the mid-east who wished the USA ill-will on 7/4. Clear Skies, Tom W. |
#14
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Why do you cool a telescope?
Mike Simmons wrote: Dan, I know your intentions are good but do you realize that your informed opinions, real data and solid references are out of place in s.a.a.? Nothing kills a good slugfest between ignoramuses like us like a bit of solid evidence. Mike Simmons Ha ! fooled you mike, typical of a California observatory, I made it all up. lies lies lies The only credibility of Mt wilson these days is the outstanding picture of planet X from the solar tower. Dan P.S. I hope you know I'm just kidding. I read every one of your posts -- even in threads I'm not interested in! |
#15
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Why do you cool a telescope?
why is the city (town? village?) called Palm Springs?
Because there are palms (in the nearby mountain canyons) and springs = (both in the nearby mtns and hot springs in the open desert). -Florian |
#16
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Why do you cool a telescope?
I figure that if you're given enough rope, Mr. Schlyter, you will eventually
hang yourself and choke to death on your anti-Americanism...and you're almost there. It has already been established that you don't know **** about history, politics, the military and we can now add deserts to the list. Don't look now, Mr. Schlyter, but your stupidity is showing. Al "Paul Schlyter" wrote in message ... In article , John Steinberg wrote: Paul Schlyter wrote: Apparently, the North American "deserts" are quite different from the deserts in Sahara and on the Arabian peninsula.... so I'd like to ask you if YOU have been in a desert? And then I mean a _real_ desert, not a "desert" with palms and springs and casinos.... Good grief! Now he's even bashing our deserts! Is there no end to your anti-Americanism? WHAT????? Are you having a severe superiority complex, or something? Do you really require your country to be the BIGGEST and BEST on ABSOLUTELY EVERYTHING ??? Sorry, but you'll just have to face the fact that the largest deserts of the world resides outside the US -- and saying so is merely stating a fact. Claiming it's "anti-Americanism" is just ridiculous !!!!!!!!!!!!!! BTW I'll readily admit that the deserts in Sweden are even smaller than the deserts in the US .... as a matter of fact they're non-existent, since we don't have any deserts here. So by your logic I've now been bashing my own country Sweden even more, and thus I have devoted myself to endless anti-Swedishism.... .... by your logic, that is, not by my logic...... evil grin Tell you what, we'll start a fund drive to have you fly over and spend two weeks in a tent in Death Valley. Then will we'll see what you think of our deserts. Probably easier to endure than the middle of the Sahara desert in, say, southernmost Algeria..... I would of course want to try them both before passing any definite judgement. P.S. Saab is owned by? Volvo is owned by? Neener, neener, neener. I know these car companies nowadays are owned by Ford and General Motors. And I couldn't care less .... to me, a car is a means of transportation, not a means to try to boast my ego.... BTW the US cars by which you drive into Death Valley would most likely fail if you tried to use them to drive across the Sahara desert... sure, they could probably stand the heat, but the sand which creeps in the machinery everywhere would make them fail perhaps after a week or two.... -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://www.stjarnhimlen.se/ http://home.tiscali.se/pausch/ |
#18
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Why do you cool a telescope?
On 11 Jul 2003 14:09:58 -0700, (Cousin Ricky) wrote:
I don't know if there really is a spring in Palm Springs, but i'm sure that the Sahara and Arabian deserts have their share of oases. On the north end of town, you can hike up into Palm Canyon, with a perennial stream under the shade of thousands of date palms. One of the richest aquifers in California lies directly under Palm Springs. The town is right at the base of Mt San Jacinto, with a height over 10,000 feet. Even though it is on the dry side, the mountains collect plenty of snow and a lot of that moisture works its way down to the east side. Deserts are created primarily by surface conditions. There are many where the water table is surprisingly high, which means oases in depressions, artesian wells, and shallow dug wells for property owners. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#19
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Why do you cool a telescope?
Paul Schlyter wrote:
BTW the US cars by which you drive into Death Valley would most likely fail if you tried to use them to drive across the Sahara desert... sure, they could probably stand the heat, but the sand which creeps in the machinery everywhere would make them fail perhaps after a week or two.... Having owned and maintained US and various European vehicles, I can't say that the better European vehicles had any advantage over US vehicles. The design and construction is largely the same. As far as dealing with deserts, liquid cooling is essential, easy brake maintenance is desirable, frequent filter and lubricant changes (daily at times) is helpful and frequent inspection of seals a must. In the US deserts, occasionally it is necessary to drive in water higher than the wheel hubs for prolonged periods. This is especially hard on the running gear wherever the car came from. I once wore out the brakes on a Wagoneer in just five miles of driving in sandy water above the door sills. Chuck -- ... The times have been, That, when the brains were out, the man would die. ... Macbeth Chuck Simmons |
#20
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Why do you cool a telescope?
Cousin Ricky wrote:
Anyway, the dust storms aren't as bad nowadays; they merely cause 50-car pileups on the highways. If there are any sand plows, i haven't heard of them, but then i don't live there. The sand doesn't pile up on the roads. The Sonoran Desert has monsoons and the biggest sand storms are in monsoon season. It is really shocking to be driving at night and have one hit. No warning. The road ahead vanishes from view instantly. You pick your way to a "safe " place to stop knowing it will rain mud soon and allow driving again. Apparently, the North American "deserts" are quite different from the deserts in Sahara and on the Arabian peninsula.... so I'd like to ask you if YOU have been in a desert? And then I mean a _real_ desert, not a "desert" with palms and springs and casinos.... Two words: Colorado River. The American lifestyle is deceptive in appearance--surely you're aware of that, given your air conditioner comment. I once read that the Colorado supplies seven states with water, and is a political hot potato in four; without it, the American southwest might well be uninhabitable in large numbers. By the time the Americans are done with it, the Wadi Colorado doesn't have enough water left to dribble into Mexico. I've heard that some southwesterners have taken to *spraypainting* their front yards to give the appearance of the obligatory American lawn--anything to make it look like they're not in the desert. When I lived in Tucson back in the 70s, I bought a place with "desert landscaping." I did not paint the lawn. This had pluses and minuses. My water bill was quite low. In wet years, the weeds were a problem. The tumbleweed in the back yard was especially annoying. The worst was a pair of century plants in the front yard that decided to bloom at the same time. I filled my F-1 truck at least 4 times carting off that disaster. I don't know if there really is a spring in Palm Springs, but i'm sure that the Sahara and Arabian deserts have their share of oases. Then of course, Palm Springs and Las Vegas aren't too far from a quaint little oasis we call "Death Valley." I think two points are being missed he 1) (off-topic) Not all deserts behave the same way. 2) (on-topic) It stays hot overnight in some places. Whether we choose to call such a place a "desert" is irrelevant. Desert areas can have pretty good seeing. I recall about 1 arcsecond as pretty common in Tucson. It is better on some of the mountains that stick up out of the desert floor. I don't have any data from other deserts. The Sonoran Desert, however, is pretty good even at lower altitudes. This has led to my utter disappointment with Colorado, however, I occasionally have access to a light bucket 150 miles from here. About 2 arcseconds is normal. Chuck -- ... The times have been, That, when the brains were out, the man would die. ... Macbeth Chuck Simmons |
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