The horizon is the line that separates the Earth from the sky. Some of the best places to see the unobstructed horizon are beaches, where the ocean meets the sky in an uninterrupted line. Here, Venus and the Moon rise together over the Atlantic Ocean horizon on the coast of Jacksonville, Florida.
The Horizon Line is the place where the ground and the sky appear to meet.It is also your eye level.
There two main types of horizons—Earth-sky horizons and celestial horizons. Both Earth-sky and celestial horizons have different sub-types of horizons.
The local horizon, geographic horizon, and sea-level horizonare all Earth-sky horizons. The astronomical horizon and true horizon are celestial horizons.
The local horizon, also called the geometrical horizon, is the visible boundary between the Earth and sky. The localhorizon may include trees, buildings, and mountains.
The geographic horizon is the apparent boundary between the Earth and sky. Mountains, trees, and other elevated features are not considered part of the geographic horizon.
The sea-level horizon is the geographic horizon at sea level. One of the best places to see the sea-level horizon is abeach. The ocean and the sky provide a clean, flat line where the Earth seems to meet the sky. If you're standing on the beach looking out at the sea, the part of the sea that "touches" the horizon is called the offing.
Celestial Horizons
Celestial horizons are used by astronomers. They aremeasurements of the position of the Earth relative to the rest of the sky.
The astronomical horizon is the imaginary horizontal planealways at a 90-degree angle from the observer's zenith (the point directly above the observer). Astronomical horizons are great circles that surround the observer.
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