Horizon

Definition

The horizon is the line where the Earth and sky appear to meet. It is the boundary separating the visible sky from the ground or sea, depending on your location.

5 Must Know Facts For Your Next Test

1. The horizon is crucial for determining the observer's viewpoint in astronomical observations.
2. Objects below the horizon are not visible because they are blocked by Earth’s curvature.
3. The true horizon and apparent horizon can differ due to atmospheric refraction.
4. The altitude of celestial objects is measured relative to the horizon.
5. Navigators have historically used the horizon for orientation and navigation at sea.

Review Questions

• Why is the concept of the horizon important in astronomical observations?
• How does atmospheric refraction affect our perception of the horizon?
• What role does the horizon play in measuring the altitude of celestial objects?

Related terms

Zenith:

The point directly overhead an observer, at a 90-degree angle from all points on their horizon.

Altitude:

The angular distance of a celestial object above or below the observer's horizon.

Meridian:

An imaginary line that runs from north to south and passes through both zenith and nadir.