Essential Astronomical and Meteorological Definitions

Sunspot

The most visible manifestation of solar activity.

Solar Activity

All the sunspots, bursting events, and associated phenomena.

Solar Cycle

The nearly periodic 11-year change in solar activity (i.e., changes in the number of sunspots, flares, and other associated manifestations).

Wolf Number

A measure of the amount of sunspots, used to quantify solar activity.

Solar Wind

Solar material flowing into interplanetary space; the Sun's atmosphere expanding radially outwards in all directions.

Climate Change

A change in the statistical distribution of weather patterns.

Weather

The state of the atmosphere at any given place and time.

Climate

The average (mean) of weather parameters over a long period of time.

Meteoroid

A small rocky or metallic body traveling through space. Meteoroids are significantly smaller than asteroids, ranging in size from small grains to 1-meter-wide objects.

Meteor (Shooting Star)

The passage of a meteoroid into the Earth's atmosphere, heated from collisions with air particles in the upper atmosphere. It is visible as a streak of light. Meteors typically occur in the mesosphere at altitudes from 76 to 100 km (47 to 62 mi).

Meteorite

A portion of a meteoroid or asteroid that survives its passage through the atmosphere and hits the ground without being destroyed.

Orbit

The trajectory (path) under the gravitational force of any body around another.

Aphelion

The point in the orbit where a celestial body is farthest from the Sun.

Perihelion

The point in the orbit where a celestial body is nearest to the Sun.

Apogee

The point in the orbit around the Earth of any object (including the Moon) where the celestial body is farthest from the Earth.

Perigee

The point in the orbit around the Earth of any object (including the Moon) where the celestial body is nearest to the Earth.

Lunar Cycle Phases

The cycle encompassing New Moon, First Quarter, Full Moon, and Last Quarter, which typically lasts 28 days.

Solar Eclipse

Occurs when the Moon passes between the Sun and Earth, blocking ("occulting") the Sun. This phenomenon happens during a New Moon.

Lunar Eclipse

Occurs when the Moon passes directly behind the Earth into its shadow.

Asteroids

Minor rocky bodies orbiting the Sun, distributed mainly in a disk located roughly between the orbits of Mars and Jupiter.

Twilight

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