By Astronomical object
Six common methods are used :
- Latitude by Polaris (Pole Star)
- Latitude by meridian altitude
- Latitude by ex-meridian
- Longitude by meridian passage of the sun
- Longitude by chronometer
- Intercept
Latitude by Polaris (Pole Star)
As the Pole Star is always around the North Pole at radius of 1°, so it is always on or near the meridian passage. The latitude of the observer can be determined. The position line runs in an east-west, or nearly east-west, direction.
Latitude by Meridian Altitude
This method is used to obtain the position line by taking the altitude of the celestial body when it is instantly on the same meridian as the observer’s. In this case, the position line runs in an east-west direction (90°-270°), and coincides with a parallel of latitude.
