Astronomical Observing and Photography


APPS: Artificial Projected Pole Star - A new rapid polar alignment method.
Updated 24 March 2019

Living in the southern hemisphere, the two stars 8' and 10' from the SCP are mags 6.8 and 7.8 respectively. Sigma Octantis at mag 5.4 is a bit over a degree away. My mount loaded up weighs 35kgs.  It's no fun pushing it around trying to find the faint pole stars while craning my neck to look through the 10mm diameter polar scope. If I don't load it before aligning it, the mount sinks into the soft ground a little after I load it sending it off alignment.

In September 2018, I designed and built myself a  simple 2-axis jig for a 50mW green laser module I purchased on ebay. I built the module into the jig. The jig attaches to the south-facing tripod leg of my EQ mount about 150mm below the polar finder.  The jig has Teflon slip discs in each axis tensioned so that the laser moves easily to exactly where I point it without jumps or jerks.  I've given it the acronym APPS - Artificial Projected Pole Star.

Using a pair of lightweight 7x35mm binoculars in one hand, I can easily see the trapezium of 5th and 6th magnitude stars and the much closer pair of 6.8 and 7.8 stars <10' from the pole. It's very easy to point the laser within a couple of minutes of the south celestial pole.  Now I have an artificial pole star that is about as bright as Jupiter with a big bright green beam leading to it.  It is very easy to point the polar finder at the artificial pole star.

I had my mate Phil put a stopwatch on me one night.  Starting with the mount set up, it took 4.5 minutes to attach the jig, plug in the power supply, point the laser at the pole then polar align the mount using the polar scope.  I've been using it regularly over the past six months and it's been fantastic. So quick and easy.  Each time the alignment has resulted in a declination drift that has been between 0" per minute up to 9.7" per minute. If > 4"/min, it is usually because the mount settled further  into soft ground so I repeat the procedure (1-2 mins) and get drift down to a negligible level.

 Teflon slip discs and nyloc nuts stop the threads from coming loose. The laser can be precisely pointed by hand.

I made my jig from machined aluminium and teflon but the jig could be made of maple or ash wood with a minimum of tools, some sandpaper and use danish wax between the sanded hardwood slip surface. 

Thisis an illustration of the view I see, first through the 7x35mm binos then through the polar finder, albeit without all the faint stars.

Below :  Some photos taken after using this polar alignment tool  with a 300mmf4 lens and using the EM200's drive but with no auto guide or manual guiding.  Each image is multiple 1-2 minute subs stacked.  The M31 image is cropped in. The others are full frame. 

While I have been using  and polar aligning equatorial mounts for more than 40 years, I have never found a method as efficient as this.

Before I hear you call out the name of your favourite polar alignment software, just bear in mind that this method takes 4-5 minutes from the time the mount is set up. That includes getting the device out of its bag, attaching, pointing the tool and aligning the mount.  Can you even set up a table and computer, connect the camera and launch the software in 4 minutes? The hardware cost me USD13 for the laser module,  $6 for the power supply. The rest was made in my workshop from scraps. Ok, so I machined pieces for the jig from aluminium however I could easily make the jig from wood and some basic hand tools.

Accuracy of course depends upon three things : -

•    Your ability to find the polar stars
•    How accurately you point the laser at the SCP
•    Accuracy of your mounts polar scope

Probably not much application for northern hemisphere observers.  Also no good if you observe with an astro club where they have lasers/ lights prohibition.

I find this method so simple, so quick, so easy, it works so well!  It has been a game changer.