Re: An easier Pasillx N & S Polar Alignment method

Joe Zeglinski

Hi Morgan,

I did pretty much the same thing as you, but in the middle of my back yard lawn.

First, I made myself a "LASER ALTIMETER" :-)

Well that is what I laughingly call it - so I could determine the precise spot in the lawn that gives me an equal elevation of clearance, above the roof of the house, and al the trees of the mini suburban orchard, I have at the back. Funny, I bought the property because of the huge, wide open sky, and quickly planted fruit trees to beautify the yard - go figure.

To make the "ALTIMETER" I needed:
- a strong rubber band
- a 5 mW green laser pointer
- and an old Heath-Zenith LCD Digital Level Meter ( any kind of hardware store digital readout, or bubble inclinometer will do)

During the day, I lashed the laser pointer with the rubber band, into a "ruler groove" at the base of the Heath inclinometer, turned on the laser, and held the contraption tightly to my waist at the belt (i.e. a fixed reference point above ground), as I slowly turned 360 degrees around with the laser hitting the eaves troughs, or top leaves of the trees. The LCD readout of the inclination angle at each turn step, gave me the average "equal elevation" angled spot in the yard, determining my artificial horizon circle, within a few inches of tolerance. If I got different angles, I moved a step aside, until all laser beam elevations were about the same. As it turned out, the elevation circle averaged about 34 degrees all around, from that potential scope setup position. For all intents, this was the exact centre of my sky view.

That night, I planted my Losmandy HD mount with AP-900 on top, in that spot, and carefully aligned the system using the PAS, and the usual two star alignment. Before I packed up for the night, I screwed plastic tent pegs at the tips of the tripod's feet, as markers for the next day's job. The following day, I dug three square holes for three of those "ready-to-assemble wall" cinder blocks, centred them on the tent pegs, and levelled the block triangle at ground level below the grass, each pointing way from centre. The white blocks are not obvious when viewed at an angle, until you are almost on top of the observing spot - no lawn mower problem or odd stones in the lawn. In winter, I will simply cover each block with a plastic garbage lid to keep it clear of snow, ready for setup - although ... I have also considered constructing igloo walls, for a winter roofless observatory around that spot (probably won't be enough city snow in the yard :-)

Now I have a perfectly levelled, north aligned, cement block pad for the tripod feet, at the spot with an even horizon elevation for my neighbourhood. I thought it was important to accurately determine the exact centre of my observing universe. I considered putting up an observatory, but that would just block the view, and uglify the yard.

As I had said in an earlier post, I determined the "ideal leg extension" for the Losmandy tripod to get the OTA to my shoulder height for installation. You should never lift a heavy OTA above your shoulders - common safe lifting practice - and I didn't want to risk dropping a slippery Questar-7 either. I then split a Chinese bamboo fork, and sawed that remaining dowel to the length of the screw channel at the base of a Losmandy pipe leg extension, using it as a "reference measurement stick", just in case the pipe leg extensions ever slip their adjustment, or I take the tripod apart for a field trip.

Tests over several system take downs, showed the set up fairly repeatable, requiring only "minor tweaks" of the AZ-EL knobs using the PAS. This is because the blocks are twice the surface area of the leg bases. I wanted them larger, just in case I needed to change the height of the OTA and thus the resulting leg spread - saves resurveying and digging up the blocks again. I also purchased those optional three Losmandy tripod feet (luminous vibration pads?), which I planned to use just on field trips, or at another spot in the yard, if it ever came up. However, I am now considering "Silicone sealing" two south facing rubber pads to the centres of their cement blocks, while leaving the north point rubber pad free on its cement pad. The reason is that the Losmandy circular "pad's holes" actually are moulded to the precise elliptical angles of the pipes. So the south pair of pads will provide a much better fixed pair of "stirrups" for two legs, and the third north pad can then be slipped on like a shoe. Otherwise, if also glued down, you would never get all three preset pipe legs into the three elliptical hole feet, very easily, without fidgeting with the pipe leg lengths - which I do NOT want to readjust). This might obviate the need to tweak the AZ-EL adjusters at all.

As you can see ... I have given this some thought, as well as the PAS camera idea. :-)


----- Original Message -----
From: "Morgan Spangle" <msfainc@...>
To: <ap-gto@...>
Sent: Thursday, September 18, 2008 9:17 PM
Subject: [ap-gto] Re: An easier Pasillx N & S Polar Alignment method

Hi Joe,

Do you set up in the same place each time? I have a permanent setup
for my C14, but for a AP600/TEC 140 that I use for visual enjoyment, I
set up on the fly - mostly on my driveway, sometimes in another spot
in the yard.

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