AS101 Study Guide - Final Guide: Lunar Phase, Tropical Year, Solar Time
Document Summary
By now you will realize that astronomy is much more precise that vague correspondences and so in this section we explore various ways of measuring important timeframes. Finally we review the development of timekeeping over the years to learn how we have arrived at our current calendar. Timekeeping by day: our local meridian is the imaginary line ending at the north and south celestial poles that cuts through our zenith. The average length of time between successive passes of the sun across the local meridian is called a solar day (this time varies slightly throughout a year which is why the word average is used). Another way of determining the length of a day is to measure the time it takes for any star to make successive passes across the local meridian which we call a sidereal day (pronounced sy-deer-ial).
