What is the measure of a straight angle?

A straight angle is defined as an angle that measures exactly 180 degrees. This angle forms a straight line when measured from one side to the other, splitting it directly into two equal halves. This definition is foundational in geometry, where angles are categorized based on their measures.

The measurement of 180 degrees signifies that the two rays forming the angle are in opposite directions, thus creating a straight line. This property is a critical aspect in various geometric contexts, including the study of parallel lines and transversals, where straight angles play a vital role in understanding angle relationships.

In contrast, angles that measure less than 90 degrees are known as acute angles, while those equal to 90 degrees are right angles. Angles measuring more than 90 degrees but less than 180 degrees are classified as obtuse angles. Therefore, the only accurate description of a straight angle among the provided choices is 180 degrees.