Astronomy & telescopes glossary - A

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Astronomy & Telescopes Glossary - E

Earthshine - Faint light reflected from the Earth onto the dark part of the moon.

Eclipse - The obscuring of one astronomical body by another as seen from the Earth. The most common eclipses are solar eclipes and lunar eclipses.

Ecliptic - Theplane defined by the Earth's orbit around the Sun. Most planets in our solar system appear close to the ecliptic plane. The Earth's axis is tilted 23.5 from the ecliptic, which causes our seasons.

ED glass - A high-quality optical glass found primarily in apochromatic telescopes. Many ED (extra-low dispersion) lenses have a high content of fluorite, which reduces aberration.

Elongation - The angle between a planet and the Sun as seen from the Earth.

Emission nebula - A nebula that emits light and glows

Encke Division - The Encke Division of Saturn splits the A Ring into two parts.

Equatorial mount - A type of telescope mount with an axis parallel to the axis of the earth. An Equatorial (or EQ) mount provides tracking of celestial objects for astrophotography when combined with a motorized drive.

Erfle eyepiece - A specific type of telescope eyepiece wich offers a wide field of view of 68 degrees or higher.

Eye Relief - The distance between the eyepiece and the eye where you can see the entire image through a telescope or binoculars. Eyeglass wearers need longer eye relief.

Exit Pupil - The diameter of light from the eyepiece that reaches the pupil of the eye.

Guide to Amateur Astronomy, Planets and Constellations

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