Degrees

Now we give an angle a number. Mathematicians divided the full turn around the centre of a circle into 360 equal parts. Each part is 1 degree, written 1°. An angle holding 30 of these parts measures 30°.

So:

• a full turn is 360°;
• a straight angle is half of that: 360° ÷ 2 = 180°;
• a right angle is half a straight angle: 180° ÷ 2 = 90°.

Why 360? Nobody knows fully. The Rigveda, one of the oldest texts of humanity, speaks of a wheel with 360 spokes, and many ancient calendars (of India, Persia, Babylonia and Egypt) had 360 days in a year. The most useful reason: 360 divides evenly by every number from 1 to 10 except 7, and also by 12 and 24. So a circle cut into 2, 3, 4, 5, 6, 8, 9, 10 or 12 equal parts has a whole number of degrees in each part: 10 equal parts are 36° each.

Look at a clock. Its 12 numbers cut the full turn into 12 equal parts, each 360° ÷ 12 = 30°. At 1 o'clock the hands are one part apart: 30°. At 2 o'clock: 2 × 30° = 60°. At 3 o'clock: 3 × 30° = 90°, a right angle. At 4 o'clock: 4 × 30° = 120°. At 6 o'clock the hands point opposite ways: 6 × 30° = 180°, a straight angle.

The Ashoka Chakra on our flag has 24 spokes, equally spaced. The angle between two spokes next to each other is 360° ÷ 24 = 15°.