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Subject: [M]: LX-200: Software back-door to the Sun
From: Mark Taylor
Reply To: mapug@shore.net
Date: Sun Mar 16 00:50:13 1997

I'm sure you have all wanted it or wished for it at some time...

To have the Sun as a pre-programmed LX-200 database object, so that
it could be used to:

* obtain good-to-excellent pointing accuracy in the daytime, allowing
you to GOTO stars, planets, and specific coordinates during daylight.
* obtain good tracking for solar/daytime observing.
* get a good alignment prior to sunset, making it possible to see
difficult near-sun (quick setting) objects without having to wait
for alignment stars to show up.
* get a good alignment prior to sunset so that any subsequent 2-star
alignment is easier (or even unnecessary) in early dusk.
* find out where *true* North/South/East/West) is without a compass
(in preparation for your nighttime setup)

Good news... It's in there!

(I'll apologize now for the length of this message up front)

This first part is based on speculation, but probably a fairly
accurate history...

[begin speculation]
Since it is *extremely* dangerous to have one's telescope automatically
point at the Sun (particularly in the case of "newbies" who might not
understand the dangers or know the proper safety procedures to follow)
Meade's management and/or "legal advisors" likely mandated that the
ability to GOTO (or near) the Sun should be expressly forbidden/unavailable
in the telescope software. And if such a feature were already developed
and working before this decision, the developers would have been required
to remove or disable it.

Assuming that happened (and being a Software Engineer myself) it seemed
likely to me that the developers would have recognized the intrinsic
value of the feature, and wanted to keep it alive in some way. Besides,
if they are anything like me they would hate the thought of eliminating
perfectly good features just because of a management decision to "cater
to the lowest common denominator in user intelligence".

Therefore, I expected that even though they couldn't publicly release
"Solar features" in the software, they may have provided a mechanism to
access the Sun for their own use: Either under the premise of being an
"unpublished test feature" for service use, or possibly even secretly as
a "back-door" that only the developers themselves would know about when
they took their own scopes into the field.
[end speculations]

The thought that "a back door might exist" prompted me to spend some
determined time experimenting with my LX-200 trying to uncover one.

I'm pleased to announce here that I have found what I was looking for...
"A back-door to the Sun".

This feature is confirmed to exist in the 3.34 ROMS used in 8"-12"
scopes, and I'm guessing that it is also in the 7" and 16" models.

I have been hesitant to publish my "find" for the same reason that Meade
presumably left the feature out in the first place -- safety. I've also
been hesitant to "go public" with my discovery for fear that Meade would
completely remove it from future ROMs if it is not supposed to be there
at all (and of course to limit their liability).

But at the same time, I couldn't deprive other LX-200 owners from having
access to such an absolutely fantastic and useful feature as this.

Besides, it's been SO DARN LONG since anyone has posted real "tricks and
hacks for the LX-200" in this forum, that I though it was about time to
get back to the original flavor of the list by doing so.
(and you thought there was nothing new to learn about these scopes!)

If you feel that you can't "responsibly handle" the information which
I am about to provide, or may not understand all of the safety issues
involved, then DELETE THIS MESSAGE NOW!!!! I am not responsible for
any harm you may bring to yourself or your equipment while trying to
look at the Sun.

Now on with the procedures....

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Published March 15, 1997 by Mark Taylor

"A BACK-DOOR TO THE SUN"

A TECHNIQUE FOR "SOLAR ALIGNMENT" OF THE LX-200

The key ingredient in "Solar Alignment" is a "back door" in the LX-200's
v3.34 database software. It is *very* simple to "unlock" this back door,
and I will describe the method momentarily.

But first I want to point out the dangers of pointing a telescope at the
Sun. It should not be attempted if you don't know what you are doing
(and take extreme care in doing it). Given that, I need to issue the
following warning and disclaimer:

***************************************************************************
DISCLAIMER DISCLAIMER DISCLAIMER DISCLAIMER DISCLAIMER DISCLAIMER
***************************************************************************
*** WARNING WARNING WARNING WARNING WARNING WARNING WARNING ***
***************************************************************************
** IT IS EXTREMELY DANGEROUS TO POINT A TELESCOPE AT THE SUN UNLESS **
** YOU KNOW EXACTLY WHAT YOU ARE DOING. THERE ARE MANY SAFETY MEASURES **
** WHICH MUST BE FOLLOWED BEFORE POINTING ONE'S TELESCOPE AT THE SUN. **
** IF YOU DO NOT KNOW AND FOLLOW PROPER SAFETY PROCEDURES, YOU COULD **
** PERMANENTLY DAMAGE YOUR EYES -- INCLUDING BLINDNESS -- OR YOUR **
** TELESCOPE AND ACCESSORIES. **
** **
** THEREFORE *DO NOT* ATTEMPT THE FOLLOWING PROCEDURES UNLESS YOU ARE **
** FAMILIAR WITH ALL THE REQUIRED SAFETY MEASURES FOR POINTING A **
** TELESCOPE AT THE SUN!!!!! I AM NOT RESPONSIBLE FOR ANY HARM YOU **
** MAY BRING TO YOURSELF IN FOLLOWING THESE PROCEDURES, AND I MAKE NO **
** WARRANTIES ABOUT THE ACCURACY OF THE INFORMATION PROVIDED HEREIN. **
** **
***************************************************************************
*** WARNING WARNING WARNING WARNING WARNING WARNING WARNING ***
***************************************************************************

CENTERING ON THE SUN (Hints and Safety Notes)
--------------------
Since the Sun is so bright, centering on it poses a few problems.
DO NOT try to use a finder scope. In fact, you should "cap" any finder
scopes or other optical equipment that you have attached to your scope
BEFORE pointing anywhere near the Sun.

For those without a Solar filter, "cap" the scope's corrector, and use
the telescope's shadow to get the fork-arms to cast equal shadows around
the tube, and to make the tube's shadow as round/small as possible. This
should be very close if you are careful. Additionally, if you have dark
sunglasses or a high pain tolerance, you can "gun-sight" up the tube by
using a front/back pair of the screws in the tube as a guide. Don't
uncap the corrector again until you are pointed well away from the sun.

If you have a Solar filter you can get extremely good centering and
therefore the best possible pointing accuracy. Mount your Solar filter
before starting the procedure, and just look through the eyepiece of
a 30+ minute FOV eyepiece to center the sun after you have done a
"shadow alignment" as described above.

THE BACK DOOR IN THE SOFTWARE
-----------------------------
The back door is only exposed only when the system is first powered on.
Once you have performed a "GOTO" action on any valid database object, the
back door gets "dead-bolted" shut. Therefore, it can only be used once
per session. But since the ability to point to the Sun is more of an
alignment tool than a necessity, it is only needed once per session anyway.

I'll note up front the important role that your alignment method plays
in obtaining good pointing and tracking accuracy. It is not enough that
you simply "unlock the back door"; *how* you exploit it also matters
quite a bit. There are two sections below which describe "Basic" and
"Refined" alignment methods.

Here are the steps:
* Assemble the telescope as usual, and situate it for a regular "Zero
Star Alignment" (described below for those who need it). The more
careful you are in this step, the better your pointing accuracy will
be once you have aligned with the Sun.
* Power up the system, and check the accuracy of your location, date,
time, and UTC values (all of these will substantially affect your
results).
* Select "Alt/Az" or "Polar" as appropriate.
* If you are really "Type A", you could cycle the power at this point to
make sure the scope "boots up" with all the preferred settings in place.
But before powering back up, re-check your "zero star" aim which will
have drifted during the time that the scope was previously running.
* Once the system is started up with a "zero star alignment", you are
ready to GOTO the Sun: Select an *invalid* GOTO target -- I think
"STAR 900" is an appropriate choice -- and hit ENTER. You will get
the usual "not in database" error. Hit the GOTO key anyway, as if it
had given you the "Stats" as it would have with a valid choice. And
off it goes to the Sun!!!!
* If you look at the data for the object you are pointing to, you will
see that it is called "NGC 0". Should you ever try to enter a zero
at the NGC prompt, you will find that it has the same effect as hitting
ENTER with a blank field -- it goes into the NGC/IC selection menu.
* Align on the Sun. How you do this alignment will affect your pointing
accuracy. Read "Basic Solar Alignment" and "Refined Solar Alignment"
below for details.
* Since the Sun is a valid object for the moment, you can SYNCH on it
(which is part of the "Basic" alignment)
* Once you GOTO something else, the "STAR 900/GOTO" process will result
in the same "invalid object" message, but will no longer GOTO the Sun.
Instead, you will be returned to the last GOTO object you used.

Note that after your initial "GOTO Sun" (and as long as you do not GOTO
anything else or get into a mode that forgets your last "GOTO" target),
you can slew around with the N/S/E/W keys and then press "GOTO" again to
return to the computed location of the Sun. This is the same behavior
you get during a normal GOTO operation.

And by the way, if you try this after sunset, you will get the "object
below horizon" message. Imagine that!

ZERO STAR ALT-AZ ALIGNMENT
--------------------------
This is a well known way to get good pointing/tracking accuracy during
the day (or even at night as a quick way to get close to your first
alignment star). Before you power on,
* Set your tripod up as level as possible. In Alt/Az, a bubble level
on the fork arms should show "level" all the way through a 360 degree
turn of the OTA.
* Make sure that the RA marks are set to Zero, and point the objective
due-south (which means the face of the plug panel is due-north).
* Make sure the OTA is level (if it is calibrated properly, the DEC
reading will be zero)
* Turn it on, and try to GOTO anything (then center and SYNCH if needed).
* To SYNCH, just hold down the ENTER key until the keypad beeps.

BASIC SOLAR ALIGNMENT (A ONE-STAR "SYNCH ALIGNMENT" ON SOL)
---------------------
If you only need approximate daytime pointing/tracking, you can use
the N/S/E/W buttons to center/SYNCH on the Sun once you have done your
GOTO. This is a software-only correction which can still leave you
with rotational errors, and will not turn on refraction correction.
As such, it is probably best done with the Sun fairly high in the sky
to minimize refraction errors in your pointing.

Of course if this is all the accuracy you are after, you could simply
set up "level and south" (the zero-star alignment described above) for
the same results.

But "Solar Alignment" is still a handy if you do not know where due-south
is with any reasonable certainty. And after you use this to acquire
better north/south orientation of the OTA, you can cycle the power and
start over with a cleaner zero-star alignment.

REFINED SOLAR ALIGNMENT (this gives the best accuracy)
-----------------------
If you want the most accurate pointing/tracking possible, you should
only use MANUAL adjustments (not the N/S/E/W keys) to center the Sun,
and you should completely avoid SYNCHing on it at all. This is called
"Refined Solar Alignment" as a play on the name "Refined Polar Alignment",
and because many of the same alignment rules apply.

For Alt/Az setups, "manual adjustment" of the azimuth means rotating the
base and fork-arms together (locked), rather than making RA adjustments
of the fork-arms relative to the base. I recommend loosening the center
bolt/knob and turning the base on the tripod (and then locking it down
again once you are in place). If you simply pick up and turn the whole
assemble (including tripod), any leveling you have done will be wasted,
and it will make the rest of the alignment unreliable.

Manual adjustment of altitude means changing the *length of* the tripod
legs with the scope mounted on top. To that end, I'd strongly recommend
first leveling the tripod and then re-checking the whole system's "level"
once the OTA is mounted (all this before even beginning the procedure).

For "Polar", manual adjustment means using the knobs on the wedge in the
same way as you do for "refined polar alignment", except that you will be
centering the Sun instead of Polaris.

And as with the "Refined Polar Alignment" process, you could wait for 15
minute increments and tweak the manual adjustments incrementally if it
drifts significantly in that time.

CLOSING NOTES
-------------
I expect that "Solar Alignment" will rarely (if ever) yield the kind
of pointing accuracy that will be obtained with "2-star/known sight"
alignment, but it sure gets you close to where you want to be in the
daytime!

---------------------------------------------------------------------------

Have Fun, and Clear Skies (Day and Night!!!!!)

Mark Taylor
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mailto:mctaylor@mindspring.com Sunnyvale, CA 37:20:54N x 122:01:56W
http://www.mindspring.com/~mctaylor/ Software Engineer, Amateur Astronomer