how are you finding true north?

[Mark Scrivener]

Over the years I have purchased various compasses (some high end), made sure I knew the local magnetic variance, and still, more often than not, my daytime alignment wound up being way off - sometimes beyond my scope's azimuth adjustment.

Buried power lines, mineral deposits, or even ferrous material on your person can swing a compass needle. If it's already dark and polaris is visible, no problem. And yes, I'm familiar with daytime alignment techniques that use pointing to the sun or another bright object. But I'm just looking for a reliable way to get my initial setup within easy adjustment range of my mount. My setup has become quite massive and "nudging" the rig after setup is no longer feasible. 

So does anyone have a method that has been successful at new/unknown sites? I've devised all sorts of techniques for getting the mount dead on with the compass (and accounting for local declination), but that all goes out the window when the local magnetic field is disturbed. 

[Jeff Crilly]

I use SkySafari AR (augmented reality) mode to see where Polaris is in the sky relative to other terrestrial landmarks.    It is still affected by local metal in the ground, etc, but the offset is automatically adjusted.   This also tells me what the elevation should be.  

Here’s a screenshot of SkySafari and where the AR button is located.  

On Jul 5, 2025, at 9:40 AM, Mark Scrivener <markwsc...@gmail.com> wrote:



Over the years I have purchased various compasses (some high end), made sure I knew the local magnetic variance, and still, more often than not, my daytime alignment wound up being way off - sometimes beyond my scope's azimuth adjustment.

Buried power lines, mineral deposits, or even ferrous material on your person can swing a compass needle. If it's already dark and polaris is visible, no problem. And yes, I'm familiar with daytime alignment techniques that use pointing to the sun or another bright object. But I'm just looking for a reliable way to get my initial setup within easy adjustment range of my mount. My setup has become quite massive and "nudging" the rig after setup is no longer feasible. 

So does anyone have a method that has been successful at new/unknown sites? I've devised all sorts of techniques for getting the mount dead on with the compass (and accounting for local declination), but that all goes out the window when the local magnetic field is disturbed. 

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[Mark Scrivener]

Thanks Jeff. After spending a bunch of time digging through Sky Safari (v7 Pro) trying to get AR working, I discovered this is only supported on iOS devices, not Android. According to their support forum, it is on the list to be added to Android. That was in 2023, so I'm not holding my breath. Arrgggghhh

But I can see how this would be great - line the sun up with landmarks (so you correct the offset), then find where Polaris will be. Brilliant. Now if they can just get Android support.......

To view this discussion visit https://groups.google.com/d/msgid/sf-bay-tac/66FCA74D-C5F8-47F8-B694-040F0551B30F%40gmail.com.

[Ted Hauter]

I use compass lite app for androids.  It even lists my address at home. Scary accurate with a bunch of ads after about 15 seconds. Lucky find as many worse apps.

One thing to mention is go-to mounts accuracy. What most people won't realize is that when centering the first object to align the scope the mount is telling us that's where the object should be. So no bubble level needed or compass on the smaller AVXs types as adjust legs and polar to place the target object in the eyepiece. When looking in the polar scope. It should be real close and close enough for observing.  A 30 sec image needs the refined adjustment of Polaris location. 

To view this discussion visit https://groups.google.com/d/msgid/sf-bay-tac/CAFv1_F0ODy5HjQVkANQcNUkuycL%2BGrmGFgex64KBiPEBk4xqeg%40mail.gmail.com.

[Jeff Crilly]

“Just” get a cheap used old iPhone or iPad to run Sky Safari pro.  Just make sure the iPad has cellular — activated cellular is not needed , but the iPad gps functionality requires the cellular hardware.  

That said… AR is not actually needed.  Assuming at least the “compass” mode works with your planetarium program  you should be able to get the gist of where Polaris is located relative to other terrestrial features.

On Jul 5, 2025, at 4:59 PM, Mark Scrivener <markwsc...@gmail.com> wrote:



Thanks Jeff. After spending a bunch of time digging through Sky Safari (v7 Pro) trying to get AR working, I discovered this is only supported on iOS devices, not Android. According to their support forum, it is on the list to be added to Android. That was in 2023, so I'm not holding my breath. Arrgggghhh

But I can see how this would be great - line the sun up with landmarks (so you correct the offset), then find where Polaris will be. Brilliant. Now if they can just get Android support.......

On Sat, Jul 5, 2025 at 1:54 PM Jeff Crilly <jeffc...@gmail.com> wrote:

I use SkySafari AR (augmented reality) mode to see where Polaris is in the sky relative to other terrestrial landmarks.    It is still affected by local metal in the ground, etc, but the offset is automatically adjusted.   This also tells me what the elevation should be.  

Here’s a screenshot of SkySafari and where the AR button is located.  

To view this discussion visit https://groups.google.com/d/msgid/sf-bay-tac/CAFv1_F0ODy5HjQVkANQcNUkuycL%2BGrmGFgex64KBiPEBk4xqeg%40mail.gmail.com.

[Jeff Crilly]

There’s also a polar alignment process that involves a goto to the sun.  

I use AP mounts which have specific park locations which are also used as part of the daytime polar alignment workflow.  

Your mount likely has goto and a similar approach can be used.  

Basically you start in a known park positions and use another park position to level the OTA using the altitude adjuster on the mount.

Slewing to the sun is then used to adjust the azimuth.  (The AP daytime method is documented in the keypad manual.)

I don’t know about other mounts, but daytime polar alignment is documented on the web in many places.   In those posts the “slew to sun” is used to adjust both altitude and azimuth.  I think this will only work reliably if the mount is quite level. 

This doesn’t help with the initial setup, but if you are close to the azimuth stops at least during the day you can reposition the tripod.  

Fwiw I’ve repositioned the AP1200 tripod with a pretty heavy load by lifting the two south feet and moving those feet slightly east or west.  (It helps to have a spotter.)

On the mach2 tripod there’s an extension tube with slotted mounting.  In that case I can loosen those bolts and rotate the mount for the rough  azimuth correction. 

[Mark Scrivener]

Hi Jeff,

Thanks. Yes, I'm familiar with the AP daytime polar alignment procedure, SB has a similar procedure, and I would assume other mounts do as well. FWIW, my main mount is an 1100AE. The issue I face is the local peturbance of the magnetic field (due to power lines, metal in the ground, etc, not declination), is sometimes great enough to exceed the azimuth adjustment range of the mount.  With a small mount this is no problem, just pick it up and rotate (or twist the top on my MyT pier), but with a large mount and large scope, this is not happening (10" portable pier, AP1100, 70lbs or more of CW's, 7" APO, etc)

Again, this is really only an issue when setting up in an unknown area for the first time, but I have been bitten more than once. If the magnetic field is perturbed, then phones/tablets will be impacted the same as a wet compass. The nice thing about AR is you could check where it claims the sun is, apply a correction, and hopefully get a much more accurate indication of where polaris is. I guess this could still be done without AR, but you would have to eyeball the correction. FWIW, I've seen asmuth errors of 15-20 deg on phone apps from some locations.

BTW - my MyT and AP400 both have provisions for rotating the entire mount if you exceed the azimuth adjustment range (much like your Mach2), but the 1100 does not. Ironically I could pick up and "adjust" the position of the entire rig with these smaller mounts if the slots weren't there. But that becomes a very dicey proposition with the much larger setups I run on the bigger mount.

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[John Pierce]

On Sun, Jul 6, 2025 at 8:10 AM Jeff Crilly <jeffc...@gmail.com> wrote:

.... but the iPad gps functionality requires the cellular hardware. 

Interesting.  My Google Pixel Tablet doesn't have GPS, and yup, is non-cellular.    But if its wifi linked to my Pixel phone, it uses the phone's GPS for its basic location functionality. 

[Alex]

You obviously want some true celestial object visible in the sky and some planetarium app (preferably on a handheld) to figure its true azimuth for the location and time (Sun, Moon, bright planet, bright star). Then you can either find your compass error by sighting at that object with it and then spotting a terrestrial feature where you would then need to approximately point the PA of your rig. Or you could have some protractor-like device incorporated into your setup to dial in that azimuth value and then point the PA indirectly by sighting into that object with some movable dial or the edge on your rig (which you would want to also calibrate first). 

I still remember from my youth (80-es) routinely dialing the manually calculated LST and interpolated from the "Astronomic Calendar" book RA and Dec of the Moon on the Zeiss 80/1200 refractor's EQ mount rings, and then kicking the frozen EQ head around until the OTA is actually aligned with the Moon observing its shadow on the snow. The clock drive would keep tracking almost perfectly for a couple of hours with just that (though the Zeiss Pier and head are quite precise machinery and all our piers were perfectly and permanently leveled on the concrete slab for every observing season).

AR in SkySafari? Forget it. Even the $3.5K Apple goggles have a cheap bad magnetometer. Study astrometry a bit - proven by ages low tech.

You also didn't mention your setup in question. Nor your observing goals. Different instruments require different approaches. 

[Alex]

Oh, just found your rig info in the later post.

N/M

[Alex]

Thus to correct my suggestion: Have a spot on your pier or nearby to level a liquid compass, sight the compass dial to the celestial object with the known Az (Mountiners compass with the slot in the mirror are the easiest option for that, or you can invest into professional one with the sighting optics), calculate the true North compass azimuth (does not matter that it's not a real absolute value, as you need only the difference with the celestial Azimuth), and rotate the pier until that value is reached by the compass handle. Just avoid changing the location of the compass between celestial sighting and dialing. Or employ a distant terrestrial pointer first, then align the mount with it. 

[Alex]

The DIY "protractor-like device", I have mentioned earlier, would work even better, e.g. you could repurpose some small finderscope (or make a trivial pip-sight) by 3D printing a simple Alt/Az head for it around some cheap 360d protractor (e.g.: https://www.amazon.com/Mr-Protractor-Protactor-Protractors-Classroom) fitting your pier top. Dial the celestial azimuth on the protractor, move the pier until the target is centered in the FOV of the finder. Done.

[John Pierce]

I had decent results standing 20 or 30 feet south of the tripod, with a mirrored compass held out in front of me, compass with the local magnetic declination preset into it, and set for 0 degrees true north, sight through the compass to the tripod, moving back and forth, when you find true north, note whats in the background exactly north of your mount, and use that as a reference for setting the mount.   This got me close enough for unguided 3-5 minute exposures at focal lengths like 200mm, and maintained pinpoint stars, using an old Vixen SuperPolaris (SP) mount.  walking around 10-20 feet usually averaged out any local deviations.