What does an apostrophe symbol after a number mean? Like in the term {75^0}20'39?

The apostrophe symbol after a number in the context you provided, such as in the term {75^0}20'39, typically represents minutes and seconds in a measurement of angles or coordinates on a map. Here's how it works:

Degrees (°): The number before the degree symbol (°) represents the degrees of an angle or a location on the Earth's surface.

Minutes (') and Seconds ("): After the degrees, you may have an apostrophe (') and a double apostrophe (") to represent minutes and seconds, respectively.

1 minute (') is equal to 1/60th of a degree.
1 second (") is equal to 1/60th of a minute, or 1/3600th of a degree.
So, in your example, {75^0}20'39 means:

75 degrees.
20 minutes (') which is 20/60 = 1/3 degrees.
39 seconds (") which is 39/3600 = 1/92.3077 degrees.
So, the total angle or coordinate would be 75 degrees, 1/3 degrees (or about 0.3333 degrees), and 1/92.3077 degrees (or about 0.0108 degrees). This notation is often used in navigation, astronomy, and other fields where precise angular measurements are necessary.