Chapter S1: Celestia Timekeeping And Navigation Flashcards
Define sidereal day
How long it takes for a star to go from its highest point in the sky to its highest point the next day
23h, 56 min, 4.09s
Define solar day
Time it takes for the sun to make 1 circuit around the local sky
24 hours avg, varies slightly by up to about 25s
Why is a solar day longer than a synodic day?
Earth moved around the sun
Define synodic month
Time between new moons
Define sidereal month
True time for it to orbit (moon)
27+1/3 days
Why is a synodic month longer than a sidereal month?
The earth moves so the moon has to move more than 1 full orbit between new moons
Define sidereal year
True time to complete one revolution
Define tropical year
Based on time between successive March equinoxes
20 mins shorter than sidereal year
Define sidereal period
Time planet takes to orbit the sun
Define synodic period
Time from when it’s lined up with sun until next similar alignment
Different because earth moves
Define conjunction
Earth, sun, planet lined up
Can’t see planet because it’s behind sun
Define opposition
Earth, sun, planet lined up
Planet is opposite sun (we see it at night)
Define planet’s greatest elongation
Two points when it appears farthest from sun in the sky
Define apparent solar time
Measuring time based on sun’s actual position in sky
Ex sundial
Define mean solar time
Average between a clock (sidereal) and sundial (solar day)
