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Observational Astronomy
Angles on the Sky
Discuss degrees of arc, arc mins, arc secs. Discuss hours or arc, minutes or arc, seconds of arc. Since a complete circle contains 24h of right ascension or 360° (degrees of arc), 1/24 of a circle is measured as 1h of right ascension, or 15°; 1/1440 of a circle is measured as 1m of right ascension, or 15 minutes of arc (also written as 15′); and 1/86400 of a circle contains 1s of right ascension, or 15 seconds of arc (also written as 15″). A full circle, measured in right-ascension units, contains 24 × 60 × 60 = 86400s, or 24 × 60 = 1440m, or 24h. – from wikipedia on RA
Discuss Celestial Sphere. Discuss RA Discuss Hour Angle.
Pixel Size and Pitch
Focal Speeds/Ratios
Telescope Limits
Diffraction
Seeing
Focus
Guide
Magnitude
Sky Brightness
Gain
Brightness
Types of Frames
Science Images
A science image or science frame is a light frame that has been calibrated to account for optical system and detector contributions or non-uniformities as well as to the top-of-atmosphere. For us, a science frame is a frame whose counts have been calibrated such that all of the counts present in the frame are thought to be proportional to the amount of spectral energy received from the source over the integration time if there were no atmosphere. It is from these frames that you can estimate most physical quantities.
Though they are often necessary, the generation of a science image for our purposes does not include astrometric calibration.
Measurements
Sources