Daytime polar alignment using a Smartphone
Aligning an Apogee fork mount using an iPhone running Sky Safari 5.
Sean Walker

Let’s say you’re all set to capture photos of the 2017 solar eclipse with your trusty scope on a Sun-tracking equatorial mount, but clouds thwart your view of the event. Your weather app tells you that conditions are much better several miles from where you’re stationed. What to do? You can race down the road with a few minutes to spare, but accurately following the Sun without polar aligning your mount in broad daylight is next to impossible. If only there were a quick way to align your scope.

You’re in luck, because there is a way to get rough polar alignment that takes about 30 seconds! All you need is your smartphone with a planetarium app installed that automatically aligns with the sky using the phone’s internal compass and accelerometer — and a flat surface on your lens cap or an equatorial wedge. Here’s how it works.

First, check to make sure the app on your smartphone has an equatorial grid function, and possibly either a crosshair or a Telrad field-of-view circle. The brightness settings on the display should be as high as possible, so you can see it in the daylight. (The planetarium apps Sky Safari and SkEye include crosshairs).

Smortphone polar alignment on an equatorial mount
Attaching your smartphone over the front of your polar finder works just as well. For German equatorial mounts without a polar scope, set the Declination to +90° and attach your smartphone to your telescope or camera's lens cap.
Spencer R. Rackley IV

Next, set up your mount with the polar axis pointed close to North. If you’re using a German equatorial mount with your lens or telescope, attach your optic to the mount, set the declination to +90°, and keep the lens cap on. Your telescope or lens cover will act as a surface perpendicular to the mount’s polar axis.

Open your planetarium app, and place the phone on the lens cap with its back flat against the cap with some tape or an elastic cord. Because the phone’s display is on top, the phone will effectively be pointing downward, toward the South Celestial Pole. With this in mind, adjusting the fine controls on the polar axis of your mount, and the EQ grid will change accordingly. Move until you see the grid align with the South Celestial Pole. Once you have the Pole centered in the Telrad circle or behind the crosshairs, you’re polar aligned!

This technique is even easier with wedge-mounted telescopes, such as my Meade LX200 and ETX EC-90, both of which are mounted on adjustable wedge-like devices to match the user's latitude. Simply remove the telescope and use the flat surface of the wedge just like the lens cap described earlier; click here to watch a video demonstration of this technique.Once you’ve aligned the wedge, install your scope and you’re ready for action.

With practice, this whole operation should take around 30 seconds. Using this method, you can be sure that your scope will track the Sun for at least 3 or 4 minutes, making that mad dash well worth the effort.


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May 25, 2017 at 5:37 pm

The article says that Sky Safari 5 has the Telrad field-of-view circle, however, it appears that the Pro or Plus versions of the program is required.

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Monica Young

May 26, 2017 at 9:38 am

Yes, that's correct - I have the regular Sky Safari app (not Pro or Plus), and it does not provide a Telrad circle.

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May 27, 2017 at 10:59 am

SkEye free on Android has 8deg and 16 deg circles that would do the trick. Going to try this on my Meade LX90 next time I get the wedge out. Only limitation I can see would be the calibration accuracy of the phone used.

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Spencer R. Rackley IV

May 27, 2017 at 1:40 pm

SkEye free is used in the video. There is some concern about magnetic offset to true north that I have heard about. The developers at SkEye say they correct for magnetic declination and have assured me that accuracy is based on "...the location you enter and the world-geomagnetic data built into the Android system."

Remember that this technique is intended for a fast setup for solar eclipses if you have to move on short notice.

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Rick Fienberg

May 29, 2017 at 10:08 pm

This is brilliant, but there's one subtlety that needs to be mentioned: the app you're using on your smartphone needs to use TRUE north rather than MAGNETIC north. Some apps do, others don't, and some do only if you have the right setting specified. For example, SkySafari Pro uses true north only if you enable location services; otherwise, it uses magnetic north. Make sure your app uses true north, and the method described by Spencer Rackley works very nicely!

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May 30, 2017 at 7:42 pm

I have tested this procedure, I think it's genius (!), and we have included it as the first step for setting up our Citizen CATE experiment telescopes. It has worked much better than using a compass app and rough sighting. There is some deflection when I touch my cell phone to the metal mount vs when it is not touching; take care with that. I am using Sky Map for Android (1.9.2), and our eclipse equipment is a Celestron CG4 tripod GEM and a Daystar 80mm refractor -- 60 of each generously donated to our project.

As Mr. Rackley says, this is a quick alignment method; our volunteers make a rough alignment using the Rackley technique first. Then they point to the Sun and use the standard image drift method to make fine adjustments to align the polar axis as follows: if the solar image drifts north (south) on the camera, move the polar axis azimuth east (west); if the solar image drifts east (west) on the camera, move the polar axis altitude higher (lower). These fine adjustments will work while the Sun is at north DEC values... i.e. between now and the 21 August eclipse.

Combining these two alignment techniques, we have been able to achieve excellent polar alignment with no measurable N/S drift during 10 minutes of time... certainly good enough for our CATE eclipse imaging experiments, and hopefully good enough for yours too. Thank-you Mr. Rackley!

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Spencer R. Rackley IV

May 30, 2017 at 11:33 pm

As Mr. Fienberg says above, make sure location services are enabled for your app. so that True north is used.

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June 25, 2017 at 6:25 pm

Hi all,
I independently thought about this technique using SkEye.
The problem is that the back of my smartphone is not flat but "nicely" curved !
So I imagined to fix it screenside on a glass plate, itself fixed on the telescope.
Any better idea except changing of smartphone 🙂 ?

Another nice app - hoping someboy would do it - would be one which would align precisely 2 smartphones in the 3 directions of space using WIFI or Bluetooth (WIFI having a better range !) ...
The main one will use its internal camera with max zoom to enable the user to visually center Polaris or even better the North Pole let say on a german equatorial mount. It would then transmit to the client app on the second smartphone on a mount which does not see Polaris all the infos about its orientation in space. The client app would show 2 dots/reticule/grids : one being the actual orientation of the mount, the second being the alignment target. Fusioning the 2 points with the Alt/Az or RA/Dec mount controls would result that the client mount will be now be also aligned !

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June 30, 2017 at 10:49 am

An alignment with this method results impossible and not applicable due to the magnetic disturbance of the metallic parts of the telescope mount with the compass of the smartphone unless a shield of an high permeability, highly expensive metal is placed in between

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March 31, 2024 at 3:00 pm

I love this. The only problem I have is my Android phone. The compass is just terrible and completely inaccurate 🙁

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Spencer R. Rackley IV

March 31, 2024 at 7:00 pm

The link to the video apparently doesn't work. Here is the original video:

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