A chart of civil time (time on your watch) versus sidereal time (ST -- time by the stars) is handy for planning a nightly observing/imaging session -- especially at odd hours when you are not sure what part of the sky is visible. Due to the relationship between sidereal time and right ascension (RA) coordinate, an object is on the meridian when the ST is equal to its RA position. The meridian, where the light passes through the least atmosphere, is the best place for observing and imaging objects.
All that is needed to create a chart of ST during a civil day is the date, observer's longitude and time zone correction. This correction is the number of hours the site is ahead or behind Universal Time -- commonly though of as Greenwich Mean Time or Zulu time. Because some places do not observe summer time or have intermediate zone corrections (30-minutes) this must be manually entered and not calculated. Note that in the Americas this will be a negative numbers of hours (example: EST = -5, PST = -8 and in summer: EDT = -4, PDT = -7).
Input Data for Chart
Chart and Explanation
How this Chart is Setup
How to Read the Chart
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