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Tropic of Cancer
2013-02-19 16:11:13

The Tropic of Cancer, which is also referred to as the Northern tropic, is the circle of latitude on the Earth that serves as a marker for the most northerly position at which the sun may appear directly overhead at its zenith. This event happens once per year, at the time of the June solstice, when the Northern Hemisphere is tilted towards the Sun to its maximum degree. Its Southern...

Prime Meridian
2013-02-19 15:54:46

A prime meridian is a meridian, i.e. a line of longitude, at which the definition of longitude is zero degrees. A prime meridian and its opposite in a 360 degree-system, the 180th meridian, create a great circle. This great circle separates the sphere into two hemispheres. If one uses directions f East and West from a defined prime meridian, then they can be named Eastern and Western...

Equator
2013-02-19 15:46:08

An equator is the intersection of a sphere’s surface with the plane that is perpendicular to the sphere’s axis of rotation and midway between the poles. The Equator is normally referred to the Earth’s equator: an imaginary line on the Earth’s surface halfway between the North Pole and the South Pole, separating the Earth into the Northern Hemisphere and Southern Hemisphere. Other...

Foghorn
2010-12-03 15:57:54

A foghorn, most often used in foggy conditions, is a device that uses sound to warn vehicles of hazards. Generally the term is used in marine transport. When lighthouses are obscured the foghorn provides an audible warning of any dangers to ships. They have been used for hundreds of years with some of the initial ones being simple bells or gongs that were manually struck. Some lighthouses shot...

Compass
2010-10-21 16:58:49

The compass is a tool that helps the user navigate using the Earth's magnetic poles by using a magnetized pointer that reacts to magnetic fields. Since a compass can be used to calculate a heading it quickly improved the safety and efficiency of travel, especially ocean travel. It has only recently been replaced by Global Positioning Systems. It works by indicating the direction of the magnetic...

Precession
2004-10-19 04:45:42

Precession -- Precession is the phenomenon by which the axis of a spinning object "wobbles" when a torque is applied to it. The phenomenon is commonly seen in a spinning toy top, but all rotating objects can undergo precession. As a spinning object precesses, the tilt of its axis goes around in a circle in the opposite direction that the object is spinning. If the speed of the rotation...

Circumpolar Star
2004-10-19 04:45:41

Circumpolar Star -- Circumpolar stars are those stars which are located near the poles of the celestial sphere. As the Earth rotates, the sky appears to rotate; and most stars will be hidden below the horizon at some point in their circular paths. A circumpolar star is near enough to the celestial pole that it will never go under the horizon. It will therefore be visibile for all the night,...

Polaris
2004-10-19 04:45:40

Polaris -- Polaris, Alpha Ursae Minoris, is the bright star closest to the north celestial pole. It is also known as the North Star, the Lode Star, or the Pole star. Because it lies nearly in a direct line with the axis of the Earth's rotation "above" the North Pole -- the north celestial pole -- Polaris is apparently motionless from the Earth, and all the stars of the Northern sky appear...

Word of the Day
bibliopole
  • A bookseller; now, especially, a dealer in rare and curious books.
This word comes from a Greek phrase meaning 'book seller.'
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