A | B |
C | D |
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G | H |
I | J | K | L |
M | N |
O | P | Q |
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| U | V | W | X | Y |
Ecliptic - The plane of Earth's orbit around the
sun, projected onto the celestial sphere. From our perspective, the sun
follows the ecliptic around the sky during the course of one year. Since
most solar system objects (planets, asteroids, and our moon) are also confined
to a similar plane, these objects appear to follow the path of the ecliptic as
ED Glass - Nothing to do with Bob Dole or Raphael
Palmero, ED stands for extra-low dispersion. Glass refracts light of
different wavelengths by different amounts, which results in the familiar prism
effect of light being dispersed into a rainbow of colors. ED glass reduces
how much the different wavelengths of light are dispersed, allowing for better
chromatic aberration correction in
refractors, camera lenses, and binoculars.
Some companies will use similar terms such as SD (super-low dispersion) and UD
Encoders - Encoders read the position of a telescope
are are used to feed back position data to a computer in a
goto telescope or digital setting circles system.
Enhanced Coatings - Glass does not transmit all of
the light that strikes it, and mirrors do not reflect 100% of the light that
bounces off them. Enhanced coatings are used to either increase the light
transmission in a refractive system or the reflectivity of a
Enhanced coating technology allows almost 100% transmission through or
reflection from a single surface. Since there are many surfaces in a
normal optical system, good coatings are critical to image brightness.
Equatorial Mount - An equatorial mount is one in
which one axis (the polar axis) is aligned with Earth's rotation axis. (In
the northern hemisphere this is done by aligning the mount with the
celestial pole, which coincides almost exactly with Polaris, the north star.)
This allows the mount to track Earth's rotation using a simple
clock drive and
eliminates any field rotation. It is, however, more cumbersome than an
alt-azimuth mount. See also
German Equatorial Mount.
Exit Pupil - The diameter of the
beam of light coming out of an eyepiece in a telescope or binocular.
Eye Lens - This is the lens in an eyepiece closest
to the observer's eye. Typically larger eye lenses offer an easier view,
although eye relief (see below) is an important factor as well.
Eye Relief - This is the distance from the eye lens
in an eyepiece to the observer's eye. Long eye relief allows observers
with eyeglasses to easily observe. Short-eye-relief eyepieces can be
difficult to view through, even for observer's without glasses.