**Classifications of Angles**

When the rays of an angle are perpendicular, the angle measures 90 degrees.

90 degree angles are called **right angles**.

One angle is smaller than another angle if it "fits inside" with both vertices at the same point. For example, the red angle is smaller than the blue angle:

Of course, the degree measure of the smaller angle will be less than the degree measure of the larger angle.

An angle that is less than 90^{o} is called an **acute angle**, and an angle greater than 90^{o} is called an **obtuse angle**.

Since any two rays with a common vertex form an angle, we could have an angle that measures as much as 180^{o} when the rays point in opposite directions:

Such an angle is called a **straight angle**, and it is nothing more than a line.