| Earth | Earth is the third planet from the Sun. Earth's diameter is 12,750 km and takes 365.25 days to orbit the Sun. | |
| Easter Moon | The name of the Full Moon usually in April. Specifically the first Full Moon after Ecclesiastical Vernal Equinox (March 21). Sometimes called the "Pink Moon," "Egg Moon," the "Pascal Moon" or the "Grass Moon." | |
| Eclipse | An Eclipse occurs when one astronomical object moves into the shadow of another. The two types of eclipses of most interest to Earthlings, are Solar Eclipses when the Moon's shadow is cast across the surface of the Earth, and Lunar Eclipses where the Earth's shadow is cast onto the Moon. Lunar and Solar Eclipses usually occur two weeks from each other. Solar Eclipse always occur during a New Moon and Lunar Eclipses always occur during a Full Moon. | |
| Ecliptic | The imaginary line across the sky representing the path of the Sun during the year. For practical purposes, it represents edge of the solar system. The Sun, Moon and all the planets, except Pluto, appear to travel along the ecliptic. The Ecliptic also intersects with the 13 zodiacal constellations. | |
| Egg Moon | The name of the Full Moon usually in April. Specifically the first Full Moon after Ecclesiastical Vernal Equinox (March 21). Sometimes called the "Pink Moon," "Pascal Moon," the "Easter Moon" or the "Grass Moon." | |
| Elara | A moon of Jupiter was discovered by Charles Perrine at Lick Observatory in 1905 . Elara is also designated as "Jupiter VII". In Greek mythology, Elara was the mother of the giant Tityus, by Zeus. | |
| Element | A substance which cannot be decomposed by chemical means into a simpler substance. | |
Elongation  Elongation |
Elongations occur when an inner planet's position, in its orbital path, is at tangent to the view from Earth. Because these inner planets are inside the Earth's orbits their positions as viewed from the Earth are never very far from the position of the Sun. When a planet is at Elongation, it is furthest from the Sun as viewed from Earth, so it's view is best at that point. There are two kinds of Elongations: The Eastern Elongation occurs when the planet is in the evening sky and the Western Elongation Occurs when a planet is in the morning sky. | |
| Emulsion | A light-sensitive coating on paper or film; consists of fine grains of silver bromide suspended in a gelatin. | |
| Enceladus | A moon of Saturn was discovered by William Herschel in 1789. Enceladus also is designated as "Saturn II". In Greek mythology, Enceladus was a giant speared in a battle by the goddess Athena and thrown into the volcano Mount Etna. Earthquakes in the area were thought to be caused by Enceladus. | |
| Encoder | A sensor or transducer for converting rotary motion or position to a series of electronic pulses. | |
| Epimetheus | A moon of Saturn was discovered by Richard Waltker (Voyager 1) on December 18, 1966. Epimetheus shares the same orbit as the Saturnian moon Janus. Epimetheus also is designated as "Saturn XI" and "S/1980 S3". In Greek mythology, Epimetheus was a Titan, who with his brother Prometheus, acted as representatives of mankind. | |
| Equatorial Mount | A type of telescope mount designed to be oriented to the movement of the sky around the North Star (Polaris). | |
| Equinox | The Equinox is a point in the Earth's orbit where the tilt of the Earth lies on the same plane as the tangent of the Earth's orbit. There are two Equinoxes each year which marks the beginning of the Spring and Autumn seasons. Literally meaning 'Equal Night', Daylight and nighttime are of equal length on the Equinoxes. Like the Solstices, the Seasons between the Northern and Southern hemispheres are opposite of each other: The Vernal Equinox in the North occurs with the Autumnal Equinox in the South and visa-versa. The Equinoxes are counter pointed by the Summer and Winter Solstices. | |
| Equuleus | The constellation "The Little Horse" | |
| Erecting Prism | A telescope accessory to give a correctly oriented image in a refractor or a catadioptric telescope. Sometime referred to as a '45 degree diagonal.' | |
| Erfle | A type of wide-angle eyepiece. | |
| Eridanus | The constellation "The Celestial River" | |
| Erinome | A moon of Jupiter was discovered by Scott Sheppard and team in 2000. Erinome is also designated as "Jupiter XXV" and "S/2000 J4". In Roman mythology, Erinome was a lover of Jupiter. | |
| Erriapo | A moon of Saturn was discovered by John Kavelaars in 2000. Erriapo also is designated as "Saturn XXVIII" and "S/2000 S10". Erriapo was a giant from Gaulic mythology. | |
| Euanthe | A moon of Jupiter was discovered by Scott Sheppard and team in 2001. Euanthe is also designated as "Jupiter XXXIII" and "S/2001 J7". In Greek mythology, Euanthe was the mother of the Graces. | |
| Eukelade | A moon of Jupiter was discovered by Scott S. Sheppard and team in 2003. Eukelade is also designated as "Jupiter XLVII" and "S/2003 J1". In Greek mythology, Eukelade was one of the Muses, and a daughter of Zeus (Jupiter). | |
| Euporie | A moon of Jupiter was discovered by Scott S. Sheppard and team in 2001. Euporie is also designated as "Jupiter XXXIV" and "S/2001 J10". In Greek mythology, Euporie was a goddess of abundance and one of the Horae. | |
| Europa | A moon of Jupiter was discovered by Galileo Galilei on January 7, 1610. Europa is the smallest of the Galilean moons and is also designated as "Jupiter II". In Greek mythology, Europa, for whom Europe is named, was one of Zeus' many lovers. She bore three sons: King Minos of Crete, King Rhadamanthus of the Cyclades, and Sarpedon. | |
| Eurydome | A moon of Jupiter was discovered by Scott S. Sheppard and team in 2001. Eurydome is also designated as "Jupiter XXXII" and "S/2001 J4". In Greek mythology, Eurydome was as the mother of the Graces by Zeus. | |
| Evening Star | Either Mercury or Venus, whichever is most prominent, when it appears in the evening sky after sunset. | |
| Eye Relief | The distance needed between the eye or the camera and the eyepiece to achieve the best field-of-view. | |
| Eyepiece Projection Photography | Astrophotography where the telescope and eyepiece is used in place of the camera lens. | |
| The "Stars and Scopes" Glossary was compiled by Peter Ue from various sources on the internet. I tried to correct and edit as much as possible, but I can make no claim or warrenty to the information here. If you find any errors just contact me and I'll try to fix it - Thanks , Peter. |
