Many people continued to believe the Earth was flat until the late Middle Ages. The horizon was interpreted as the sharp edge of the Earthalthough no one ever reached it.
The horizon also helped prove that the Earth was a sphere. As early as 330 BCE, the Greek philosopher Aristotle noticed that certain constellations in the southern sky rose higher from the horizon as he traveled south. This could only be possible if the Earth was round.
the distance above sea level.
clear or obvious.
person who studies space and the universe beyond Earth's atmosphere.
imaginary horizontal plane always at a 90-degree angle from the observer's zenith (the point directly above the observer).
the art and science of creating and operating aircraft.
narrow strip of land that lies along a body of water.
line separating geographical areas.
line or planes used as reference for observation and measurement relative to a given location on the surface of the earth or another celestial body, and referenced to positions at right angles to the location's zenith.
determining an object's position using the stars and planets as guides.
sharing of information and ideas.
group of stars that form a recognizable shape.
to illustrate or show.
to raise higher than the surrounding area.
system of satellites and receiving devices used to determine the location of something on Earth.
largest circle that can be drawn around a sphere, such as the Equator.
line where the Earth and the sky seem to meet.
left-right direction or parallel to the Earth and the horizon.
plan or occurrence that creates a false belief.
line where Earth and sky seem to meet but are blocked by elevated features of the landscape, such as trees or mountains. Also called the visible horizon.
process of determining length, width, mass (weight), volume, distance or some other quality or size.
to plan and direct the course of a journey.
front end of an aircraft.
part of a body of water that touches the horizon.
path of one object around a more massive object.
at a right angle to something.
representation of volume or depth on a flat surface.
person who steers a ship or aircraft.
flat surface of two dimensions (length and width).
wireless transmission based on electromagnetic waves.
ray extending from the center of a circle or sphere to its surface or circumference.
person who works aboard a ship.
base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle.
to communicate using signs.
constellation visible in the Southern Hemisphere.
rounded and three-dimensional.
system of communication involving devices connected through electrical wires.
imaginary plane that passes through the center of the Earth, perpendicular to the radius of the Earth.
able to be seen.
line where Earth and sky seem to meet but are blocked by elevated features of the landscape, such as trees or mountains. Also called the local horizon.
point on the celestial sphere directly above a given position.