Wndsn Quadrant Telemeter Tutorials
Making the most out of our graphical telemetry computers.
Like with many complex instruments, there are multiple ways to solve certain problems and to measure the required inputs. Combining the various functions leads to a multitude of advanced uses.
Determining Local Latitude
The local latitude corresponds to the angle between the horizon and the pole star.
To determine latitude (in the Northern hemisphere), we are sighting Polaris. The pole star, or Polaris, is useful because its angle to the horizon does not change with longitude or time. Also, Polaris is almost in line with the Earth's axis and hence can be used to determine North. From latitude 0° on the equator, Polaris is exactly on the horizon, i.e. it has an angle of elevation, or altitude of 0°. Conversely, from the North pole, the angle of elevation, or altitude is 90°. Therefore, the measured altitude of Polaris is equivalent to the local latitude.
Note that a measurement precision of e.g. 0.5° translates to 30' of latitude, or 30 nautical miles.
- The latitude is the angle between the plumb line (which extends into the zenith) and the perpendicular to the sighting line; zero on the quadrant.
- Polaris, the sighted star, is measured at 30° from the horizon.
- The latitude at the location measured is thus 30°.
Measuring Local Latitude at Night
If we identify a star that is on or near the celestial equator, and we measure its maximum altitude at culmination, we can easily calculate our local latitude.
A usable star is Mintaka (δ Orionis), the right-most star in the belt of Orion. Mintaka is 0.3° (or 18 minutes of arc) below the celestial equator.
- We measure the altitude of the star with our Quadrant at the moment of the meridian passage, that is when the star is due south; 37.2° for Mintaka.
- Then, we add the difference of 0.3°, to get the altitude of the celestial equator; 37.5°.
- Subtracting that altitude from 90° gives us our latitude on Earth; 52.5° for our sample position in Berlin.