Blind Smart-phone Polar Alignment

How do you align your telescope's equatorial wedge when you can't see Polaris and don't have equipment with automatic alignment? For a long time I've done this with a compass and a level or their smart-phone equivalents. A few weeks ago I found a much better way, using only one app to make both adjustments; illustrated in a Sky & Telescope video on You Tube with Spencer Rackley.

Like the compass and level technique, this approach will work day or night anywhere in the world. The altitude and azimuth settings of your wedge are adjusted using only a planetarium app on your smart-phone. I use SkySafari, but almost any app with a virtual reality live sky view will work. The easiest placement of the smart-phone on your wedge or mount points it towards the ground. This results in aligning to the celestial pole that is not visible in your sky. In the Northern Hemisphere we use the south celestial pole for alignment. It helps if you smart-phone or case has a flat back like the iPhone, but you can probably make almost any one work. This procedure works for a fork mounted telescope using an equatorial wedge.

  • First level your tripod and orient the mount wedge roughly in the direction of the celestial pole.
  • Open your smart phone planetarium app and activate an aiming reticle and a virtual reality live sky view.
  • Hold your smart phone against the mounting plate on the wedge. In the northern hemisphere the smart-phone will be pointing in the opposite direction from Polaris. Your planetarium app should show the sky near the south celestial pole.
  • Adjust your wedge altitude and azimuth settings to center the south celestial pole in the reticle shown in your planetarium application.
  • Remove your phone and mount your telescope on the wedge.

You now have a reasonably good polar alignment even during daylight. If needed, you can refine your alignment using a drift alignment procedure. If you have a German Equatorial Mount the procedure is similar, except that you will need to set and lock your mount Right Ascension and Declination adjustments so that your telescope mounting plate face points towards the celestial pole.

Problems?

With any compass based alignment - fences, decking, or other near by objects with lots of iron in them may interfere with a good alignment by distorting the earth's magnetic field. Over the years I've gotten good results with both a compass and level and with my iPhones. Almost all of my solar system images are made after just a blind alignment. I only do a drift align for long exposure DSOs or if I have a problem keeping my subject framed over a typical 3 minute run of short exposures.

If you have problems with the compass in your phone, try this to trigger a recalibration: Make sure that you have your phones location services enabled and swing your phone in a large figure 8 motion.

If problems persist, check your telescope wedge and mounting hardware. Is it all non-magnetic materials like plastic, aluminum, or stainless steel? Run a small compass around your hardware to locate any magnetic parts. Replace steel hardware with non magnetic hardware if possible. Placing your phone symmetrically between any magnetic hardware will minimize problems.

Comparing your electronic compass readings with a precision magnetic compass may reveal any repeatable errors due to your phone's hardware. Record any deviation and adjust for it in your alignments. Check your phone's level by rotating the phone in place on any surface and checking for a consistent reading.

Using a planetarium app should offer the same accuracy as your phone's compass and level, with the convenience of being able to adjust both azimuth and altitude at once using a single convenient placement of the phone.

Content created: 2017-06-17

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