What is an Angle?
An angle is the space between two straight lines that meet at a point. Imagine two rays of light shooting out from the same spot—the opening between them is an angle. You see angles everywhere: the corner of a room, the hands on a clock, and even the way a door opens.
The point where the two lines meet is called the vertex (pronounced VER-tex). The two lines themselves are called rays or arms of the angle.
Think of it like opening a pair of scissors. The point where the two blades join is the vertex, and the two blades spreading apart create an angle between them.
How Do We Measure Angles?
We measure angles in units called degrees, shown with a tiny circle symbol: °. A full circle is divided into 360 degrees. This might seem like a strange number, but ancient mathematicians chose it because 360 can be divided by many other numbers, making it very useful.
Here are some common angles you should know:
A right angle is exactly 90 degrees (written as 90°). This is what you see at the corner of a square or a piece of paper. A straight angle is 180 degrees—it's completely flat, like a straight line. A full rotation brings you all the way around to where you started: 360 degrees.
Think of it like a pizza. A whole pizza is 360°. If you cut it into four equal slices, each slice is 90°—one right angle.
Using a Protractor to Measure
A protractor is a tool shaped like a semicircle with numbers around the edge. These numbers go from 0 to 180 degrees. To measure an angle, you line up the middle point of the protractor (the centre mark) with the vertex of your angle. Then you line up one ray with the 0 degree line, and read where the other ray points to on the scale.
Acute angles are smaller than 90°, obtuse angles are between 90° and 180°, and reflex angles are larger than 180°. Once you understand this simple system, you can measure any angle you encounter!