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Glossary
Telescopes and Astronomy Gear terms, explained
Short, plain definitions of the words you'll see on product pages and spec sheets. Each one links to a guide when there's more to know.
A
- Aperture
- The diameter of a telescope's main lens or mirror. Read the guide →
C
- Collimation
- Aligning a telescope's mirrors or lenses. Read the guide →
D
- Dobsonian
- A Newtonian reflector on a simple rocker-box mount. Read the guide →
E
- Exit pupil
- The width of light leaving an eyepiece. Read the guide →
- Eye relief
- How far your eye sits from the eyepiece lens. Read the guide →
F
- Focal length
- The distance over which a telescope or eyepiece brings light to focus. Read the guide →
- Focal ratio
- Focal length divided by aperture, such as f/6. Read the guide →
G
- GoTo
- A computerized mount that points to objects automatically. Read the guide →
I
- ISO 12312-2
- The international standard for direct solar viewers. Read the guide →
L
- Live stacking
- Combining many short exposures in real time. Read the guide →
P
- Polar alignment
- Aligning an equatorial mount with the celestial pole. Read the guide →
S
- Seeing
- Atmospheric steadiness, which limits sharpness at high magnification. Read the guide →