sidereal month
Moon's orbital period
A sidereal month is the time it takes the Moon to complete one orbit around Earth relative to the fixed stars—about 27.3 days.
This differs from the more familiar lunar month (roughly 29.5 days), which measures the cycle from new moon to new moon.
The difference arises because Earth is also moving around the Sun, so the Moon must travel a bit farther to return to the same phase.
Distinct periods in sequence
- waxingCoating for shine
- waningGradually decreasing in intensity
- crescentCurved sickle-like arc
- gibbousConvexly swollen shape
full moon · new moon · lunation · moonrise · moonset · lunar cycle · moonlight · lunar eclipse
Violent governmental overthrow
- eclipticSun's apparent annual path
- perigeeOrbit's closest point
- apogeeHighest orbital point
- ellipticalOval-shaped or indirect
trajectory · orbital · inclination · node · eccentricity · barycenter · gravitational · angular momentum
Date-tracking system
- timekeepingMeasuring duration's passage
- durationLength of existence
- intervalDuration between two points
- periodicityRecurring at regular intervals
astronomical unit · ephemeris · almanac · calculation · precision · reference frame · fixed stars
Stars appearing motionless
- constellationNamed pattern of celestial bodies
- zodiacCelestial belt of signs
- celestial sphereImaginary dome of stars
- declinationAngular distance from equator
celestial equator · vernal equinox · star field · Polaris · epoch · parallax
phases
Distinct periods in sequence
gibbous · full moon · new moon · lunation · moonrise · moonset · lunar cycle · moonlight · lunar eclipse · blood moon
revolution
Violent governmental overthrow
elliptical · trajectory · orbital · inclination · node · eccentricity · barycenter · gravitational · angular momentum · velocity
calendar
Date-tracking system
- timekeepingMeasuring duration's passage
- durationLength of existence
- intervalDuration between two points
periodicity · astronomical unit · ephemeris · almanac · calculation · precision · reference frame · fixed stars
fixed stars
Stars appearing motionless
- constellationNamed pattern of celestial bodies
- zodiacCelestial belt of signs
- celestial sphereImaginary dome of stars
declination · celestial equator · vernal equinox · star field · Polaris · epoch · parallax
- moonfull moon, lunar, crescent moon, new moon, half moon
- calendarscalendar, calendar day, calendar year, lunar calendar, almanac
- celestial cycleslunar cycle, solar cycle, lunar phase, orbit, eclipse
- time unitssecond, minute, hour, seconds, day
- Babylonian astronomycuneiform tablets, clay tablets, astrolabe, astrolabes, zodiac
- Lunar MonthsMuharram, Ramadan, Nisan