Alternative Alignment Techniques?

[ecuador]

I've been offering "daytime" polar alignment in my app Polar Scope Align Pro for iOS. Users have been using it a night when they have no alternative, with varying results given how sensitive phone magnetometers are to local interference. I thought that I could offer users an option to compensate for interference with an extra calibration step, so the current beta version of the app being tested has a new tool (tentatively) called "Laser / Hop Alignment", intended for people who have a polar scope, but can't view the polar star (Polaris obstructed, or σ Oct too faint etc), or people who only have a Laser pointer for alignment (e.g. for the MSM rotator), and it works a bit like this:

- You start with the phone mounted on the telescope (while it's pointing at Dec 90), or the saddle directly so that its top is pointing where the RA axis is pointing - no real precision is required for this as long as the phone is not moved during the process. You open the tool and first you get a list of suggested bright stars over your horizon that are not too far off the celestial pole (also a button to use any star up to Mag 5.0), and you choose one that you can see.

- Then, you move your mount in alt/az (even move tripod if the star is far away) and put the star you selected in the center of your polar scope, or as the target of your Laser. The app will try to guide you, but it can be ignored at this step as it is uncalibrated.

- After pressing "Calibrate" the app will know how much your magnetometer is off by using the reference "hop" star and will compensate for that, guiding you to the Celestial Pole.

The app already has a Push-To tool for Dobsonians and when using an interim "hop" to calibrate the magnetometer, it gets you within 30 arcsecs of the target even with metal parts nearby, so I am expecting the polar alignment to also benefit.

Apologies for not being able to support Android, but if any iOS users want to try out this beta, you can just PM me with your email.

[OzEclipse]

Ecuador's app looks very interesting and I have asked Dimitrie if I can Beta test his app for the southern hemisphere. I am hoping it is a resource I can point my students towards if they are struggling with polar aligning their trackers.

But the purpose of this post is to post yet another technique that I call

The Google Earth Polar Alignment Method

If you know exactly where you will be setting up your gear you can use Google Earth (not Google Maps) to align your mount even during the day. I tried this one afternoon last week. Sky was predicted to clear at 2am and I wanted to photograph the Kreutz comet 2020 X3 (ultimately unsuccessful) at 4am low on the southeast horizon if it was bright enough. My front deck is floored in slightly bouncy thick-sheet (fibre-cement sheeting) however the concrete landing at the top of the stairs with open sky overhead is 4" solid concrete topped on a brick staircase structure. Quite solid! It also gave me a clear view to that horizon.

First step was to launch Google Earth (GE), find my house, and activate the ruler tool. Google Maps does not have this ruler tool which is why GE is used. I started the ruler right at the landing and drew a line due south 180 degrees until it intersected with some landmarks that were easily recognisable. The edge of a small shed on an adjacent property some 150m away was precisely due south. This method is independent of magnetic interference. My house is all steel construction, cladding, roof and structural components for termite resistance and so any magnetic method won't work.

Note: I am in Australia, the southern hemisphere, obviously in the northern hemisphere you point north. If however, there is a convenient landmark in the opposite direction to your pole, you can always align the mount simply by aligning and looking from the opposite direction but the polar axis must always point to your pole.

I set up my EM200 mount and aligned the straight edge of the mount with the gap between the two shed buildings and exactly on the edge of the smaller shed on my neighbours property. If the landmark doesn't precisely align, consider changing your telescope location so that you have a precise N or S reference.

After setting the azimuth, I used a clinometer app on my iPhone to set the polar axis elevation to my latitude. After dark, I checked using the polar finder and I was almost exactly on the south pole. So close that I didn't bother to adjust.

Another variation of this method is if you have a driveway or other ground structure visible on GE, you can measure the orientation of the structure on GE then cut yourself a triangular template with the angle between that feature and due south or north. Place the template against the side of your mount and align the other edge with the driveway edge.

I first devised this technique when observing a total solar eclipse from near Shanghai in 2009. We set up on a long straight concrete sea tidal / storm wall near the Donghai Bridge south of Shanghai which we had scouted and selected prior to arrival in China using Google Earth and Google Maps street view. The site looked good and on the wall, it was unlikely anyone would be able to stand in front of us. However, we were sure it would have a lot of steel reinforcing causing problems with compasses. Using the triangular template, the polar axes could be set at 64.5 deg to the wall. There were four mounts in our group requiring alignment. Using the template and a clinometer, I worked my way around each member of the group and used the template technique, new to everybody to align all four mounts over a period of 15 mins. Being able to sight along a very long length of the wall cancelled out any small variations in the alignment of the wall.

Cheers

Joe