HIGH TEMPERATURE WARNINGAN IMPORTANT ADVISORY FOR ALL TELESCOPE USERS !!
by: Clay Sherrod
And the Livin' Ain't So Easy for your telescope!
We have all been through one of the hardest winters on record and perhaps the first cold weather for many telescope users. Through this we have learned a LOT about the computerized GO TO telescopes, a lot we wish we did not have to know:
1) cold weather drastically affects the mechanical performance of the best of telescopes because of the heavy green grease and lubricants that gum up in sub-freezing temperatures; the only solution to that problem as we have discussed is to "de-grease" ("Performance Enhancement Guide....Part 1", here on the ASO GUIDES);
2) the required 12V (or in some cases 18v) power during cold months is adversely affected in very cold weather, usually beginning below 27 degrees F and getting worse the colder it gets; after battery power gets too low, motor function and GO TO accuracy can become next to impossible;
3) Computerized telescope handboxes are most definitely temperature sensitive at the same cold range. It must be kept warm, and it must be supplied with no less that a constant 10V before your display begins to talk to you in "Martian" and the keypad commands to the computerized scopes becomes inoperative.
But we're through all that right!? Summer is coming, and the "...livin' is easy." Until the sun bakes your electronics or melts adhesives onto your optics or until temperatures get so warm on your precious telescope awaiting nightfall on some August afternoon, that the very glues that hold your secondary baffle in place, or until your circuit boards no longer can "resist" nor "capacitate"....
Welcome to the perils of summer and hot temperatures. We are in for another bout of temperature-related telescope frustrations and failures. I want to alert all telescope users to the dangers that can cause irreparable harm to their telescopes, the circuitry, and particularly to the optics, the telescope, the mount and the handbox and all electronics - SOME OF THIS HAS BEEN BASED ON ACTUAL TESTS that I have just completed on standard electronic controllers of Meade and Celestron telescopes.
You are likely to be surprised...even if you are a seasoned "veteran" user of the telescope that you now own.
YOUR TELESCOPE IN SUMMER HEAT - Part 1: Optical Tube Assembly, Mount, Accessories
Following is a quick checklist of (P) potential heat-related problems with the telescope and mechanical equipment itself and (S) the solution to prevent the situation from occurring; and/or (R) the "remedy" if that particular heat stress DOES result in down time or damage to your telescope.
P1 - Leaving the telescope in the hot sun uncovered.
S1 - Simply don't do it....it is never a good idea. The only solution to this (like setting up for a weekend star party where your scope must be left outdoors) is to cover the scope with a CANOPY, not a tarp. A tarp or even a sheet (NEVER COVER YOUR SCOPE WITH PLASTIC as this traps moisture which can ruin the scope and its circuitry) will still build up a significant amount of heat under it, particularly if tied at the bottom. Use a CANOPY instead, and THEN cover the telescope with a sheet beneath the canopy; since the canopy does NOT rest directly on the scope, air is allowed to circulate and continually cool in the shade of the suspended canopy.
P2 - Leaving the telescope in the hot sun COVERED.
S2 - See above....NEVER DO THIS!
P3 - Internal Heat in the telescope OTA
S3 - A big problem taking out and setting up your scope early, particularly with the Maksutov design and only a bit less with the LX Schmidt-Cassegrain, is that a closed optical tube assembly (OTA) will build up the day's heat. This can cause two problems of significance:
1) Long cool down time to observing.
R3 - use the Canopy discussed in S1, above to keep the scope as cool as possible during the day;
R3b - wait until dusk or slightly before to take the scope out into the evening air and allow AT LEAST one hour for the Newtonians and catadioptics and TWO hours for Maksutovs and larger SCT type telescopes to reach thermal equilibrium.
R3c - you can use the "CHIMNEY TRICK" to accelerate cooling of any closed tube OTA. DO THIS CAREFULLY to prevent the accidental entering of debris or dust into the OTA! All you need to do is to orient your telescope so that the LENS (front of the scope) IS FACING TOWARD THE GROUND! Remove the end cap of the scopes or the prism screw mount from the back opening until the rear of the scope is OPEN; in the ETX you will need to flip your small mirror as you would to"view" straight through the scope (you will be able to see the secondary through the opening in the correct position). Place a clean lightweight cheese cloth (or similar lace-like fabric) OVER this opening to block dust and debris.....and then merely wait about one-half the time! Your scope will cool internally TWICE as fast, as the port acts like a chimney, rapidly dispelling warm air otherwise trapped inside the tube!
P4 - Excessive Heat Damage to the OTA
S4 - Safeguard as in S1; however, likely damage that can occur is in the cements that are used within the OTA, particularly that holding the secondary baffle tube to the meniscus lens of many catadioptic telescopes. This thin metal baffle is held in place ONLY by a thin ring of adhesive that becomes like jelly when the temperature gets excessive in the scope. [ NOTE: This does not apply to the Schmidt-Cass. scopes!]
R4 - If your baffle DOES become loose and begins to slip, you will know it; before you can actually SEE this with the eye, you will notice flares from images of bright objects like Mars and bright stars, flares that you did not have before. If you notice this, unfocus (turn your focus know counterclockwise) and look at the out-of-focus image....you will see the "disk" pattern of the star; if it appears oblong rather than circular, then your baffle tube has slipped. It will be necessary to carefully UNSCREW the entire end cell that holds the meniscus lens from the OTA (it may take some work to get it moving at first and be very careful not to damage the pretty blue tube!). Once out, you can get a replacement adhesive ring from the manufacturer OR you can merely use a very good temperature-resistent glue (something that never actually "hardens" but remains flexible as the temperature changes) VERY sparingly against the flat edge of the baffle that mounts to the glass; use the MIRROR itself (the secondary) as a circular template to place the baffle....let dry for about two hour in a protected environment and then reattach via screwing the cell and its lens back onto the OTA firmly (no need to do any alignment whatsoever).....and that's all there is to it!
P5 - UV Fading of Telescope Exterior
S5 - Even if kept indoors and covered, light from windows and even in shade can eventually bleach the beautiful colors of your modern scopes. I highly recommend (in addition to keeping out of direct light) using TURTLE WAX's new "Scratch Gone" soft wax for new car finishes. This comes in many colors and that is the key to buying it....if it is Turtle Wax soft and it has a choice of colors, you are getting the RIGHT product. It has a UV block and is excellent for both the BLACK PLASTIC (and metal on the LX) and the blue tube. Use this very sparingly (just moisten your rag with it) and rub gently and even on all surfaces....then buff. It resists fingerprints, UV sunlight, and makes your scope look like a million bucks!
P6 - Telescope Electronic Circuitry (OTHER THAN Computerized Handboxes)
S6 - During tests of AutoStar on 90+ degree days in mid-summer 2001, I also exposed the mounting of an ETX 125 and LX 90 (less tube assemblies) to the same temperature/sun exposure as the AutoStars. These conditions would closely simulate about a two-hour observing session of the sun with the sun at its highest point during the day. The temperature on both days reached at least 92 degrees F. in my observatory for a prolonged period of two hours of direct sunlight. ALTHOUGH SOME DISPLAY PROBLEMS AROSE WITH AUTOSTAR, there were NO adverse conditions resulting to the internal telescope circuitry or electronic function within the drive motors/encoders whatsoever.
P7 - Protecting your Optics from Direct Sunlight
S7 - It is easy if you are readying for a star party to inadvertently allow the direct sun's rays to enter your telescope assembly; you should always (for your safety and that of the scope) point the telescope in any direction away from the sun. If outdoors, REMEMBER YOUR FINDERSCOPE; direct sunlight will MELT the crosshairs within about 8 seconds flat as the sun might inadvertently pass across the field of that little scope!
P8 - Accessories Left in Sunlight
S8 - Your eyepieces and ALL accessories should be kept in shade. NEVER put your accessory case out in direct sunlight, not even for 10 minutes. It is like a little greenhouse and WILL RUIN your eyepieces, particularly any of them (and many do) that have cemented components; if you carry a flashlight in your accessory case, it too can be damaged by excessive heat.
P9 - Transporting your Telescope Cargo in Your Vehicle in Summer
S9 - NEVER, NEVER lock up the telescope in the trunk of your car, even while the car is moving at 70 mph down the freeway toward vacation. The inside of your trunk does not understand the chill factor of the speed and sunlight bearing down on the metal trunk lid will eventually heat that interior upward to 150 degrees F. I always recommend, if possible, transporting the scope and accessories in the back seat and all non-temperature-sensitive parts (i.e., the tripod, wedge, charts) in the trunk.
YOUR TELESCOPE IN SUMMER HEAT - Part 2: Computerized Handboxes - EXTREMELY IMPORTANT - PLEASE READ!
Just when we thought we were getting our controllers away from the environmental perils of winter's cold....here comes summer's HEAT. And, boy if you thought you had "cold temperature problems" this past winter, please take notice here!
P10 - Battery Power and Hot Weather
S10 - not a problem...unlike winter months, your internal batteries (or your external DC power station) actually will provide a somewhat enhanced output during summer, provided they do not get excessively hot.
P11 - Prolonged Exposure to Handbox of Direct Sunlight for Long Periods of Time - MALFUNCTION!
IMPORTANT NOTE: The following descriptions are what prompted me to write this very important guideline to summer safety for the ETX and LX 90 telescopes. As I was training the motors on a "Supercharged" ETX one afternoon I began to run into some serious malfunctions related to AutoStar that at first I could not identify. After examination and further testing the next day in 92-degree heat with TWO AutoStars, it was learned that direct exposure to sunlight is VERY detrimental to your AutoStar and will result in AT LEAST the following two situations in less than 10 minutes of exposure:
[DO NOT ATTEMPT TO DUPLICATE!!! Permanent Damage to YOUR Handbox Will Result!]
1) the AutoStar or other brand controller LED display will no longer function, although the commands of the handbox can still be entered; what you will get will be a LED display of filled "boxes" all the way across both lines of your display screen; this will NOT go away until handbox has cooled for about 30 minutes, but your problems are NOT over;
2) not all commands entered into handbox once the display goes blank (#1 above) result in proper functions being obeyed; again, about 30 minutes is required before the handbox cools to where some commands can be rightfully accepted;
3) speed settings on handbox ( for example, the number keys "9" fastest, "1" slowest become totally inoperative and everything runs at the fastest speed when handbox becomes overheated; NOTE: letting the handbox cool down as above DOES NOT always result in your speed function returning; and so,
4) a total RESET (obviously requiring all new user data entry, owner info., site specifications, telescope type AND "Train Motors" will be necessary) must be done to put the handbox back into normal operational mode once it has become overheated by exposure to the sun.
I used both of my "test handboxes" and was able to (thank goodness) successfully revive both after the alarming results of only 12 minutes in sunlight. It is important to note that this is NOT a "maybe this won't happen to me" situation....it will. I ran the test throughout two successive days on a hot muggy April week here in Arkansas, and believe me, it will do it over and over again.
So, I go back to my 50-year-old rule that I have preached to all telescope users, even way before microprocessors took the place of Magnusson Setting Circles, before Maksutovs began outperforming my old Unitrons.....
....NEVER subject your telescope to any condition - permanent or temporary - that you would NOT subject your 6-month-old infant child. They are BOTH just as sensitive....and certainly BOTH are just as temperamental and difficult to please!
Arkansas Sky Observatory