## What is Zenith Angle?

The zenith angle is the angle between the sun’s rays and vertical at any given point on Earth.

**Key Takeaways:**

- Zenith angle refers to the angle between the sun and vertical.
- Zenith angle and solar altitude angle will always add up to 90°.
- The sine of the zenith angle will always equal the cosine of the solar altitude angle, and vice versa.

## Understanding Zenith Angle

The solar zenith angle is the angle that is formed between the sun and vertical (or straight up) at any given point on the earth. For instance, if the sun was straight in front of an observer at the horizon, the angle between horizontal and vertical would be 90°. Whereas, if the sun were directly overhead the zenith would be 0° because there is no angle between it and vertical.

Zenith is closely related to solar altitude angle, which is the angle between the sun and horizontal. Since the sum of the solar altitude angle and the solar zenith angle will always equal 90°, the sine of one angle will equal the cosine of the other. Both can be calculated using the same formula that ancient mariners used to navigate the ocean.

The solar zenith angle is particularly useful for determining if the sun is rising or setting and in predicting solar effects on radio communications. And, of course, in planning the optimal solar array set up.

## Related Terms

Tilt Angle – Also known as the elevation angle, the tilt angle is the angle above horizontal at which a solar panel is mounted.

Azimuth Angle – An azimuth angle is a measurement to denote the angle between an observer and the sun, relative to the local horizon. At its most simple, the azimuth angle is the compass direction from which sunlight is shining.

Photovoltaic Array – A photovoltaic array is a collection of one or more solar panels that are connected together in order to collect a greater amount of solar energy.