Relationship between angles, degrees and nautical miles on the Earth's surface

Longitude and latitude are based on degrees. The equator and every meridian are divided into 360 degrees.

An great circle is a circle around a sphere whose center is the same as the center of the sphere. The length of a great circle is always equal to the circumference of the sphere, and it always divides the sphere into two equal halves.

A small circle is a circle on the surface of a sphere whose center is located somewhere other than the center of the sphere.

All meridians are great circles. Of the lines of latitude, only the equator is a great circle. All other lines of latitude are small circles.

A nautical mile is one arc minute along a meridian. This means that the distance from the North Pole to the equator is 90 × 60 = 5400 nautical miles, and the distance around the Earth along the equator is 360 × 60 = 21600 nautical miles. In fact, every circle around the Earth whose center is at the Earth's center has a length of 21600 nautical miles, assuming the Earth is a perfect sphere.

The original definition of a kilometer is that the distance from the North Pole to the equator via Paris is 10,000 km. Thus, the circumference of a great circle on Earth is 40,000 km. A nautical mile is therefore 40,000 km / 21,600 = 1.851851852 km. In 1954, the length of a nautical mile was standardized as 1852 meters.

C o n t e n t s

• Determining position from stars
• The night sky
• The celestial sphere
• What you see at the North Pole as the Earth rotates
• How the night sky changes when you travel to the equator
• The effect of Earth’s rotation on the sky at the equator
• The celestial meridian, upper culmination and lower culmination
• Changes in star altitude at the North Pole, equator and in between
• Declination
• Example of determining latitude
• Hour angle, Greenwich Hour Angle (GHA)
• Aries, Greenwich of the celestial sphere
• Sidereal hour angle (SHA)
• Local hour angle (LHA)
• Relationship between time and hour angle
• Example of determining longitude and latitude from the Sun at noon
• Kulmien, asteiden ja meripeninkulman suhde toisiinsa maapallon pinnalla
• Shooting circle
• Azimuth
• True bearing to a star
• Nautical triangle
• Solving the nautical triangle (altitude calculation)
• Position fixing from stars using the Marcq Saint Hilaire intercept method
• Star identification
• Details and practice
• Time
• Time difference (ΔT)
• Altitude measurement
• Example of position fixing
• Twilight
• Calculating twilight time
• Navigation association exam