Test 1

Front 1

Rotation

Back 1

Spin on an axis.

Front 2

Revolution

Back 2

The orbiting of one body around another.

Front 3

Inclination

Back 3

Or an orbit, the angle of the plane of the orbit with respect to the ecliptic plane.

Front 4

Summer and Winter Solstice

Back 4

The point on the celestial sphere of northernmost or southernmost declination of the Sun in the course of a year; colloquially, the time when the Sun reaches that point.

Front 5

Vernal and Autumnal Equinox

Back 5

An intersection of the ecliptic and the celestial equator. The center of the Sun is geometrically above and below the horizon for equal lengths of time on the two days of the year when the Sun passes the equinoxes; if the Sun were a point and atmospheric refraction were absent, then day and night would be of equal length on those days.

Front 6

Seasons

Back 6

One of the four natural divisions of the year, spring, summer, fall, and winter, in the North and South Temperate zones. Each season, beginning astronomically at an equinox or solstice, is characterized by specific meteorological or climatic conditions.

Front 7

Astronomical Unit

Back 7

A unit of length used in measuring astronomical distances within the solar system equal to the mean distance from Earth to the sun, approximately 150 million kilometers (93 million miles).

Front 8

Waxing

Back 8

To increase gradually in size, number, strength, or intensity.
To show a progressively larger illuminated area, as the moon does in passing from new to full.

Front 9

Waning

Back 9

To decrease gradually in size, amount, intensity, or degree; decline.
To exhibit a decreasing illuminated area from full moon to new moon.

Front 10

Crescent

Back 10

The figure of the moon as it appears in its first or last quarter, with concave and convex edges terminating in points.

Front 11

Gibbous

Back 11

More than half but less than fully illuminated. Used of the moon or a planet.

Front 12

Umbra

Back 12

The completely dark portion of the shadow cast by the earth, moon, or other body during an eclipse.
The darkest region of a sunspot.

Front 13

Penumbra

Back 13

The grayish outer part of a sunspot.
2. (Astron.) The shadow cast, in an eclipse, where the light is partly, but not wholly, cut off by the intervening body; the space of partial illumination between the umbra, or perfect shadow, on all sides, and the full light. --Sir I. Newton.
The faint shade surrounding the dark central portion of a solar spot is also called the penumbra, and sometimes umbra.
(Paint.) The part of a picture where the shade imperceptibly blends with the light.

Front 14

Node

Back 14

Either of two diametrically opposite points at which the orbit of a planet intersects the ecliptic.
Either of two points at which the orbit of a satellite intersects the orbital plane of a planet.