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Table
of Contents
Telescopes
Terminology
Purpose
Atmospheric
Nomenclature
Questions
Intro
to Astronomy
Misconceptions
Archaeoastronomy
Equitorial Coordinates
Understanding the Seasons
Time & Its Measurement
Solar & Lunar Eclipses
The
Solar System
The
Earth
The
Moon
Mecury,
Venus, Mars
The
Outer Planets
Solar
System Debris
The
Sun
Evolution
of Stars
Intersteller
Matter
Sky
Literacy
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Basic Telescope Terminology
- Aperture: The diameter of the light collecting area of
the telescope. A telescope with a lens or mirror six inches in diameter
would have an aperture of six inches.
- Focal Length: The distance from the center (lens) or surface
(mirror) of the light collector to the position of best focus of
the image.
- Refractor: A lens or series of lenses brings light to a focus.
- Reflector: A mirror or series of mirrors brings light to a
focus.
- Focal Ratio: The aperture of a lens or mirror divided into
its focal length. The focal ratio of a telescope is the key to understanding
the usefulness of a particular instrument. See magnification and
field of view for a clearer explanation.
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Aperture
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Focal Length
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Focal Ratio
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Usefulness
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(in inches)
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(in inches)
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3.5
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50.4
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F/14.4
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lunar & planetary |
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6
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24
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F/4
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wide field |
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8
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56
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F/7
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all-purpose |
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10
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100
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F/10
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all-purpose |
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26
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442
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F/17
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lunar & planetary |
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200 (Hale, USA)
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1000
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F/5
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wide field |
F/1 - F/5, wide field - star clusters, nebulas; F/6 - F/10, all-purpose;
F/11 - F/30, narrow field - lunar and planetary.
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