Sidereal Month. Interval between two successive transits of Moon across the same star. Value is 27 days 7 hours 43.2 minutes.
Sidereal Period. Time taken by a planet to make one revolution of its orbit.
Sidereal Time. Time based on hour angle of First Point of Aries.
Sidereal Year. Time taken by Earth to go round its orbit when a fixed star is taken as a point of definition. Length is 365 days 06 hours 09 minutes 10 seconds.
Side Skids. Vertical timbers suspended over ship's side to keep cargo clear of side when loading or discharging.
Side Stitch. Running seam put in alongside seam of a sail to give additional strength. Sighting. Observing with the eye. Applied to document, means examining and signing as evidence of satisfaction as to its authenticity.