Month

If “month” sounds to you like the word “moon” then it should remind you that a month lasts about as many days as a complete cycle of moon phases. New moon to first quarter, waxing crescent; first quarter to full moon, waxing gibbous; full moon to last quarter, waning gibbous; last quarter to new moon again, waning crescent. A phase of the moon doesn’t represent a position of its orbit, but how the sun strikes it as it orbits Earth. The moon orbits Earth in less than 28 days and it takes more than 29 days to complete a rotation relative to the sun. Left as an exercise for the student: Match the type of month to its definition. In column A: sidereal month, synodic month, tropical month, anomalistic month, and draconic or nodical month. In column B: The moon’s orbital period relative to the stars. The moon’s orbital period relative to a line joining the sun and Earth. The time it takes the moon to pass twice across Earth’s equator. The time it takes the moon to return to the point where it’s the closest to Earth. The time it takes the moon to pass through two the points where its orbit passes through Earth’s orbital plane.