Meteor Glossary

Anthelion - Meteoroids striking the Earth from a direction opposite the Sun. (For example, if the Sun is just rising above the eastern horizon, the "anthelion point" would lie on the other side of the sky, just below the western horizon.)

Apex - The direction the Earth is traveling toward located 90 degrees west of the sun. Meteors seen from this direction will be the fastest of all since they orbit in a retrograde orbit and the encounter the Earth in a "head on" collision. Apex radiants are separated into north and south branches due to the lack of meteors with zero inclination. The centers of these two branches are located 15 degrees north and south of the ecliptic, 90 degrees west of the sun.

Culminate - To reach one's highest point. Meteor showers are best seen when their radiants culminate in the sky when they seen highest above the horizon. This occurs either in the due north or south directions, depending on a radiant's declination and the observer's latitude.

Degrees - A unit of measurement in the sky. One degree equals the diameter of two full moons. The length from the horizon to the point straight up in the sky (zenith) is 90 degrees. Most meteors are usually 5 degrees or less in length.

Ecliptic - The path in the sky as seen from Earth taken by the sun, moon, and the planets. Many meteor radiants are situated on or near the ecliptic. This path includes the 12 constellations of the zodiac plus a few other obscure constellations not generally recognized.

Fireballs - Meteors which appear of magnitude -3 or brighter. This is brighter than any of the fixed stars.

Magnitude - A measure of an objects brightness. The dimmest meteors one can usually see is 6th magnitude. The lower the magnitude the brighter the object. For instance the full moon is magnitude -13 while Venus usually hovers near magnitude -4. The brightest stars are of magnitudes -1, 0 and +1.

Meteoroids - A speck of space dust from a comet or an asteroid.

Meteor - The bright streak of light in the sky that we can see when a meteoroid burns up in Earth's atmosphere.

Meteorite - If a meteoroid does not completely disintegrate in the astmosphere and pieces of it land on Earth intact, we call the surviving fragments meteorites.

Persistent Trains - Streaks of light that remain in the sky after the meteor itself has disappeared.

Radiant - The area of the sky where shower meteors seem to originate. Related meteors can appear in any part of the sky but a line drawn backwards to where they intersect will reveal their radiant.

Radiant Coordinates -- A meteor shower radiant located at "01:56 (029) +55" corresponds to Right Ascension = 1h56m and declination = +55o. The number in parentheses is the Right Ascension in degrees.

Sporadic - Random meteors not associated with any known shower.

Waxing - Generally referring to the moon's phase, an increasing portion of illumination on the moon's disk that occurs between new and full.

Zenithal Hourly Rate (or ZHR) - The rate of meteors that an observer under very dark skies would see if the radiant were overhead. The ZHR is almost always greater than the actual number of meteors a sky-watcher can see. [more about ZHR]