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The zenith is the imaginary point in the sky located directly above an observer. Picture standing outside and tilting your head to look straight up. The point that would align with the top of your head is known as the zenith. This point is unique for every observer at their specific location and can be an excellent reference point for determining other celestial positions. The zenith is considered the highest point in the sky from your viewpoint, distinct for everyone depending on where they are standing on Earth. It also serves as a crucial anchor in astronomical observations for measuring and contrasting positions of other celestial objects.

Altitude, in astronomy, refers to the angular distance of an object above the horizon as seen by an observer. It's essentially how high an object appears in the sky. The altitude is measured in degrees, with 0° at the horizon—the line where the sky seems to meet the ground—and 90° when an object is at the zenith. For instance, if a star is halfway between the horizon and your zenith, its altitude would be about 45°. Identifying the altitude is essential in locating objects in the sky and understanding their motion relative to the horizon.

• 0° at the horizon
• 90° at the zenith

Predicting and tracking objects through their altitudes can enhance one's ability to navigate and study celestial phenomena.

The zenith angle is an essential concept connected closely with altitude. It refers to the angle formed between your zenith and a line drawn from your position to a celestial object. This angle helps in expressing how far an object is from being directly overhead. The zenith angle is calculated by subtracting the altitude from 90°, since the range from horizon to zenith is 90°. For example, if a star has an altitude of 30°, then its zenith angle would be: \[\text{Zenith Angle} = 90° - 30° = 60°\]
By understanding the zenith angle, astronomers can better understand an object's current position, making navigation and plotting observations much easier and accurate. Both zenith angles and altitudes are complementary tools for fully covering the position of celestial objects in the night sky.