Common sun-based techniques for discovering true (astronomical) north include:
If the sun is not cooperating, you can always find true north using:
- A gyrocompass- This is by far the best method. The sensors at BRU2, OSOP’s international seismic station, were oriented using OSOP’s gyrocompass. Finding a Russian-made gyrocompass for 25,000 to 100,000 USD on Ebay is easy. Getting it to your place without raising suspicion that you are developing a missile guidance system for your homemade bomb can be tricky. Then there are the risks you run of violating international and domestic laws by shipping your new toy. And, of course, the expense!
- A magnetic compass- a widely used and completely haphazard way of finding true north. Like anything else, the preferred technique depends on the final application. Magnetic compasses are perfect, cheap solutions for orienting seismometers for civil defense applications but they are not appropriate for orienting your Nanometrics Trillium 120.
- A single handheld GPS
- A dual GPS receiver with an integrated inclinometer (like the “Azimuth Pointing Systems” made by MultiWave Sensors)
- Artificial intelligence (Coming soon)
Finding true north is “…simple in theory, but there are many complications in practice.” (Ringler et al., 2013). For a comparison of the methods listed above and their resulting orientation errors see:
Ringler, A.T. et al. (2013) Seismic Station Installation Orientation Errors at ANSS and IRIS/USGS Stations. Seismological Research Letters 84, doi: 10.1785/0220130072
As Ringler et al. (2013) points out, with many of these methods finding true north is one third of the battle. Sources of error also include transferring the reference line and then aligning the seismometer to that line. Orienting a seismometer to within a few degrees of true north without a gyrocompass is an art that often involves a bit of luck and a splash of black magic.
P.S. The documents included in this post were made available to me many years ago while I was working at the IG-EPN in Ecuador through Kyle E. Persefield, a USGS Albuquerque Seismological Laboratory Contractor. Thanks again Kyle for these excellent step-by-step guidelines.