Astronomy and related astronomical terms

1. A chart providing the future positions of celestial bodies: An ephemer is a table listing the future positions of the sun, moon, and planets over a given period of time.
2. An annual publication containing astronomical tables: In an ephemer there are lists of the positions of the celestial bodies that occur throughout the year.

The official system of mean solar time: An ephemeris time was a method used to calculate data for tables of changing astronomical phenomena (ephemerides).

The movement of an object, or celestial body, along a circular path (epicycle): According to the geocentric Ptolemaic system, planetary orbits have two components: a circular or deferent orbit around the parent body; and a smaller circular orbit, or also called an epicycle motion, around a point on the deferent orbit.

The "deferent" is the large circular orbit around which a planet was thought to orbit, in one or many epicycles.

"Epicycles" are circular orbits within orbits that were used to (incorrectly) describe the orbits of objects in the Ptolemaic system (about 150 A.D.

Epicycles and deferents were used to predict orbits until Kepler discovered the elliptical nature of orbits (early in the 1600s).

A telescope mount with one axis parallel to the earth's rotation axis, and the other at right-angles to it.

This equatorial mount enables the telescope, once locked onto a star's position, to track or to follow the star using a motor drive to compensate for the earth's rotation.

Most large telescopes are mounted in this way, but the altazimuth mount, with its simpler construction, is becoming more popular.

An "altizimuth mount" is a mounting for astronomical telescopes that has separate axes for horizontal and vertical rotation.

Because celestial objects move in arcs across the sky, tracking their motions with an altazimuth mount requires adjustments of both axes.

The two times of the year when the sun crosses the equator and night and day are of equal length: One equinox usually occurs on March 21st (spring equinox) on September 23 (fall equinox).

One of two points at which the ecliptic cuts the celestial equator.

The vernal equinox is the point in which the sun, traveling on the ecliptic, crosses the celestial equator from south to north.

The sixth largest constellation, which meanders from the celestial equator deep into the southern hemisphere of the sky: Eridanus is represented as a river. Its brightest star is Achernar, a corruption of Arabic for "the end of the river".

The minimum speed with which an object must be projected for it to break free from the gravitational pull of a planetary body: The escape velocity describes the effective separation from the gravitational field of a star, planet, or other celestial body.

A projectile must have a minimal velocity which has been worked out in a special formula.

The organization of European countries which is dedicated to the exploration of space research and technology: The European Space Agency was founded in 1975 with its headquarters in Paris, France.

The combined processes of evaporation, sublimation, and transpiration of water from the earth's surface into the atmosphere: Evapotranspiration is the total loss of water from a particular area, equal to the sum of the amount of water lost by evaporation from the soil and other surfaces and the amount lost by transpiration from plants.

An older star that has converted most or all of its store of hydrogen into helium: An evolved star is a star that is nearing the end of its existence when most of its fuel has been used up.

This period of the star's duration is characterized by loss of mass from its surface in the form of a stellar wind or the ejection of gas off the surface of a star.

Many different types of stars, including our sun, have stellar winds, however a star's wind is strongest near the end of its existence when it has consumed most of its fuel.

A planet that orbits a star other than the sun: Exoplanets are detected by observing their star's "wobble" which the exoplanet's gravitational attraction causes.

Scientists have spied a new exoplanet and not only is it the biggest one yet, but it’s also moving in the wrong direction

Unlike other planets, which orbit in the same direction as their stars rotate, "WASP-17" moves in the opposite way, according to a study published in Astrophysical Journal.

Instead of traveling around its host star in the same direction the star spins, like all other known planets, but this abnormal planet is orbiting backwards. Scientists think the renegade orb, named WASP-17, got flipped around during a near collision with another planet during its early development.

Planets are born from the same ball of rotating gas that creates their parent star, which is why they usually orbit, and spin, in the same direction as their "mother star". While WASP-17 is the first planet known to orbit backwards, some planets in our own solar system, such as Venus, are spinning backwards. Like WASP-17, Venus may have experienced some kind of collision during its early history, which threw it into an unusual spin.

Researchers at "South African Astronomical Observatory" discovered the new exoplanet 1,000 light years away from Earth. In addition to its surprising orbit, the exoplanet stands out because of its size; in that, being only half the mass of Jupiter but twice its volume, the researchers claim WASP-17 is now the largest known planet.

WASP-17 marks the 17th exoplanet discovered by the "Wide Angle Search for Planets", or WASP project, conducted by eight universities in the U.K.

Because exoplanets don’t give off any light of their own and are usually obscured by their super-bright host stars, the scientists find exoplanets by scanning hundreds of thousands of stars, looking for the subtle dimming that occurs when a planet passes in front its parent star.

The outermost layer of the earth's atmosphere.

The exosphere goes from about 400 miles (640 km) high to about 800 miles (1,280 km). The lower boundary of the exosphere is called the "critical level of escape", where atmospheric pressure is very low (the gas atoms are very widely spaced) and the temperature is very low.

A feature of our universe deduced from the observation that the distant galaxies' light is red-shifted.

Observations so far have not succeeded in determining whether the universe is open (of infinite extent in space) or closed (of finite extent) and whether the universe in the future will continue to expand indefinitely or will eventually collapse back into an extremely dense, congested state.

Outside of, or beyond, our galaxy: such as, the Milky Way Galaxy.

The astronomical field that deals with objects beyond the Milky Way; especially, galaxies and quasars.