Angle Detectives: Right, Acute and Obtuse

Look around the room right now. Can you spot the corner of a book, a door frame, or a table? That corner makes a shape — and that shape is called an angle. Some corners are perfectly square. Some are more open. Some are more closed. Today you are going to become an angle detective and name exactly what you see.

An angle is the amount of turn between two straight lines that meet at a point. We measure angles in degrees, written with a small circle symbol like this: °. A RIGHT ANGLE is exactly 90°. It looks like a perfect square corner. The corner of this page, the corner of a door — all 90°. We mark a right angle with a tiny square drawn in the corner. An ACUTE ANGLE is less than 90°. It is a sharp, pointy angle. Think of the top point of a capital letter A — that is an acute angle. Any angle between 0° and 89° is acute. An OBTUSE ANGLE is more than 90° but less than 180°. It is wider and more open than a right angle. The hands of a clock at 10 o'clock make an obtuse angle. Any angle between 91° and 179° is obtuse. A quick memory trick: ACUTE sounds like 'a cute little angle' — and it really is small and pointy!