Using digital inclinometer app and compass to roughly polar align Star Adventurer

[jman17]

Hi,

I am wanting to do a rough alignment of a SkyWatcher Star Adventurer using a compass and digital inclinometer app on the ipad and am not sure of what exactly to do. From what I have read I use the compass (from 3 metres away to not put out the compass) to point the Star Adventurer to true South, then use the digital inclinometer to more accurately input my current latitude on the tracker. I'm not sure of exactly how to use an inclinometer to do this and was wondering if anyone could guide me through exactly what to do? Thanks if anyone could help.

jman17

[jimmyh1555]

Where abouts are you? First thing you must do when you use the compass to find True South (180 degrees), is to find out the Magnetic Variation for your location. Either look up on a good map, or google up your location and ask for magnetic variation, as well as your latitude and longitude. If the magnetic variation in your area is X degrees East, then subtract X from 180 and that is the number to point the magnetic needle at. ie if it is 14 degrees East, then get compass needle to point to 180-14=166 deg. When it is pointing to 166 degrees, then the fore and aft marker on compass will be pointing to True South. If your Magnetic variation is 14 deg West, then ADD 14 to 180 - ie 198deg. point needle to 198 and the fore and aft mark will be pointing to True South. I do not know what that inclinomoter is, but you must point the telescope upwards from horizontal the same number of degrees as what your latitude is. My latitude here in TAS is 41 degrees South. I have made up a simple right angled triangle of plywood using high school geometry. One angle in the triangle is equal to my latitude of 41 degrees, one angle is at 90 degrees, and the other angle is 49 degrees (the three angles must add up to 180 degrees). Mark the correct angle! Then I just lay the long side of the triangle on the body of the scope, and get a bubble level and put it on the top of the triangle. Adjust the angle of the telescope until the bubble level shows the top of the triangle is level . Hey presto, your telescope is pointing up at your exact latitude! Hope this helps.
I used the compass feature on my iphone once, and each time I used it, it pointed in a different direction! So beware - best to use a proper magnetic compass.

[jimmyh1555]

sorry, 198 degrees should be 194;)

[Shano592]

I will use my case to explain about the inclinometer.

I have a scope with a wedge as an option. With the wedge, I have an equatorial scope. Without it, my scope is Alt-Az mounted, and useless for long exposure imaging.

When the wedge is mounted, the tilt (or incline) of the mounting face needs to be set to 90 degrees, less my latitude. My latitude is 33.3 degrees south, so, the mount face needs to be set at 56.7 degrees (90 - 33.3), in order to be pointing straight at the south celestial pole.

[jman17]

Hi,

I think I am getting the idea. I live in Toowoomba so would point the unit to 169.47 degrees. With using the inclinometer does it have to be done every time if at the same latitude? Would it be accurate to set up the mount with my camera etc and place my ipad with the 'Clinometer' app on the top part of the L bracket where the camera goes (I attached a photo for reference) as it seems to be on the same incline as the polar scope, check the angle of incline and then adjust accordingly? I plan to look into getting a right angled triangle like you mentioned and try this method in the meantime if suitable.

jman17

[OzEclipse]

Depends what you mean by "the unit."

If you are referring to the polar axis & you point the polar axis at 169.5 magnetic bearing you will be off by 21 degrees. Jimmy's instructions are correct but need to be read very carefully.

There are two ways to use a compass, be it a magnetic compass or an ipad app. Both ways illustrated below indicate true south. The one on the left is much easier to use. Get the north compass needle to point to 10.5 or the south needle to point to 190.5 (10.5 is the magnetic declination for Toowoomba). Then the N & S dial indicators on the compass protractor and the edge of the compass/iPad all point north/south. You can use the method on the left in which case, yes, point the polar axis at 169.5.

If you are using iPad that has GPS, I'd suggest using an app called Spyglass. You can adjust the settings so that it performs the magnetic dec correction automatically and displays true bearings. It also uses the camera and superimposes the compass on the camera image. Works a treat.

This page has an AGRF calculator for any location and explanations of the sense of D with examples.

http://www.ga.gov.au/oracle/geomag/agrfform.jsp


Joe

[doug_parkes]

a great way to find absolute True North without using a compass.
Drive a rod or stick into the ground so that it casts a good shadow.
Using your Sky Safari app (or similar) determine the azimuth of the Sun (a good sky simulation app will give a continuous readout of the Sun's azimuth). When the Sun's indicated azimuth is 000º the shadow cast by your rod or stick is exactly aligned to true north. Drive a tent-peg or similar into the ground at either end of the shadow to have a semi-permanent position of the north-south direction. Set your polar axis to align with this true north shadow. Next, adjust the altitude of the polar axis to agree with your latitude and your telescope won't be far off being correctly polar aligned.

[ZeroID]

Better done with a plumb bob so it is nice and vertical. That's how I started my Observatory build. Nice long Solar noon shadow to mark Nth\Sth.