19 Understanding Degrees
We can measure angles in degrees. There are 360 degrees in one full rotation (one complete circle around).
The degree symbol = °
We use a little circle ° following the number to mean degrees.
For example, 90° means 90 degrees
A full circle is 360°
Half a circle is 180° (called a straight angle)
The quarter of a circle is 90° (called a right angle)
Why 360 degrees? Maybe because of old calendars (such as the Persian Calendar) used 360 days for a year – when they watched the stars they saw them revolve around the North Star one degree per day.
Also, 360 can be divided exactly by 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 30, 36, 40, 45, 60, 72, 90, 120 and 180, which makes a lot of basic geometry easier.