Leap Day Trivia (or, Is the Moon a Moon?)

February 29 does not happen every year. In fact, it happens only about once every four years. This unusual day has caused me to do some interesting research about time, which ended in a question about whether or not the moon is a moon.

  • The three units of measuring time that pertain to leap years are the day, the month, and the year. In the simplest mathematical model of the solar system, the earth turns on its axis once a day. The moon travels around the earth once a month, and the earth and moon travel around the sun once a year.
  • The passage of a day is noted by the cycle of daylight and darkness. The Roman definition marks a day as beginning at midnight, but the Hebrew definition marks a day as beginning at sunset (by tradition, when it is dark enough to see two stars in the sky).
  • The Hebrew definition is based on the repeated statement in Genesis 1, “It was evening and it was morning, the (first, second, third, etc.) day.”
  • The passage of a month is noted by the position of the moon in the sky, as well as by the phases of the moon. The phases are caused by the fact that sometimes the side of the moon facing the earth is fully lit by the sun (a full moon), sometimes partly lit by the sun, and sometimes entirely in the moon’s shadow. Technically, a new moon is not the fully darkened disc of the moon, but the first crescent of sunlight reflected by the moon visible on the earth.
  • About twice a year, the moon moves through the shadow of the earth. This is a lunar eclipse, and it can be seen from much of the earth when it happens. About twice a year, the moon’s shadow falls upon the earth. This is called a solar eclipse. Because the moon is much smaller than the earth, a solar eclipse is seen only in a small part of the earth.
  • Eclipses do not happen every month because the moon’s orbit usually keeps the sun, moon, and earth from being aligned so that shadows are seen on the earth or the moon.
  • The passage of a year is noted by the change in seasons, usually best marked by the equinoxes—when daytime and nighttime are the same length—and by the solstices—when daytime and nighttime are as much unequal as they can be. The inequality at the solstices depends upon location on the earth—the difference is negligible near the equator but highly significant near the north and south poles.
  • The inequality in daytime and nighttime are caused, not by the orbit of the earth around the sun, but by the tilting of the earth upon its axis. The change in tilt, though, goes through its cycle exactly once each year.
  • The earth is closer to the sun in January than it is in July. The warmth of summer in the northern hemisphere is not due to the distance between the earth and the sun; it is due to the amount of sunlight the hemisphere receives during the day.
  • A year is 365.2425 days, or 365 days, 5 hours, 49 minutes, and 12 seconds.
  • A month is about 25.53 days, or 29 days, 12 hours, 44 minutes, and 3 seconds.
  • The length of a year can be changed very slightly by a major earthquake.
  • The length of a month varies slightly because of the effect of the sun’s gravity upon the moon.
  • There are about 12.3685 months in a year.
  • Most ancient calendars had twelve months in a year, with an extra month added every three or four years to keep the seasons from drifting through the year. The calendar used by Muslims has twelve months every year, resulting in a year of 355 days. Therefore, Muslim holidays move through the seasons and are roughly ten days earlier every year according to the Gregorian calendar.
  • In the Roman Republic, priests in Rome declared when an extra month should be added to the year. They sometimes misused this power for political purposes, adding an extra month to the time that they or their friends in politics could exercise power over Roman law.
  • Julius Caesar changed the Roman calendar, making each month except February have either thirty or thirty-one days. In the Julian calendar, a month does not begin with a new moon. Julius Caesar also said that February would have twenty-eight days every year and a twenty-ninth day every four years.
  • The Julian calendar went into effect in the Roman year 708, which is now called 46 BC.
  • The month of July is named for Julius Caesar. The month of August is named for Octavian Caesar, Julius’ relative, who seized power after Julius Caesar was assassinated. The Roman Senate made Octavian the first Emperor of Rome and gave him the title Augustus.
  • A monk who taught at the University of Paris, Johannes de Sacrobosco, noticed around 1235 that the seasons had drifted several days in the Julian calendar. Sacrobosco also perpetuated a myth that Caesar Augustus had stolen a day from February to make his month of August the same length as July. Archaeological evidence has disproved this myth; July and August always had thirty-one days in the Julian calendar.
  • Pope Gregory XIII reacted to Sacrobosco’s discovery by ruling that three times in four hundred years the leap day should be omitted. If the number of the year is divisible by one hundred but not by four hundred, it is not a leap year. Therefore, there was no February 29, 1900, and there will be no February 29, 2100. There was, however, a February 29, 2000.
  • The Gregorian calendar went into effect in October 1582.
  • Pope Gregory only had authority to change the calendar in parts of Italy; however Roman Catholic kings in Spain and Portugal made the same change in their countries and colonies, and France followed suit fairly quickly. Protestant and Orthodox countries did not change as quickly: Great Britain and its colonies did not adopt the Gregorian calendar until 1752, and Russia did not switch to the Gregorian calendar until 1918.
  • Pope Gregory’s change in calendars resulted in dropping ten days from October 1582. By 1752 this required a change of eleven days, and by 1918 it required a change of thirteen days.
  • The omission of days was protested by many people, not from superstitious reasons, but for very practical reasons. Many people were paid by the day or the week, but they had bills such as rent due every month. Therefore, the omission of several days caused financial difficulties in their lives.
  • Some people adjusted their birthdays to conform to the Gregorian calendar. George Washington, for instance, was born on February 11 in the Julian calendar but celebrated his birthday on February 22 after the switch to the Gregorian calendar.
  • Until the invention of mechanical clocks less than one thousand years ago, hours varied in length depending upon the time of year. An hour was one-twelfth of a day and one-twelfth of a night. Daytime hours were longer in the summer and shorter in the winter; likewise nighttime hours were shorter in the summer and longer in the winter.
  • The counting of hours worked backward and forward from noon, which was defined as the instant when the sun reached its highest point in the sky for any location. This highest point is called the meridian, which is represented by the letter m in a.m. and p.m.
  • Rapid travel by railroads led to the adoption of time zones around the earth. Travelers did not appreciate changing their watches in every town and city to match the local time, and railroad schedules were hard to create before time zones were adopted. Because of time zones, noon on a clock can be as much as thirty minutes away from the actual meridian.
  • Because of daylight saving time, noon on a clock can be as much as ninety minutes away from the actual meridian.
  • If not for time zones and daylight saving time, a full moon would be at the moon’s meridian at midnight. The first quarter moon would rise at noon and reach meridian at sunset, and the third quarter moon would rise at midnight and reach meridian at sunrise.
  • The moon was the only object so named until Galileo aimed a telescope at the planet Jupiter and detected four of its satellites, which he called moons.
  • Jonathan Swift wrote in 1726 that Mars has two moons. Swift also described their size and the speed of their travel around Mars relatively accurately. The moons of Mars were not detected by scientists until 1877.
  • A planet is described as an object of a certain size moving around a star. Refinement of that definition resulted a few years ago with the omission of Pluto from the list of planets in our solar system. Planets have been observed circling other stars in our galaxy.
  • A moon is described as an object moving around a planet. Usually moons are much smaller than the planets they circle. If two objects circle one another while moving around a star, they are called a double planet system.
  • Astronomers disagree among themselves about the size distinction required to identify a moon-and-planet system or a double planet system. Various ratios have been proposed, but universal agreement has not yet happened.
  • One rule suggested for distinguishing a moon-and-planet system from a double planet system is locating the center of orbit of the smaller of the two bodies. If the center of orbit is within the larger body, the smaller body is a moon. If the center of orbit is outside the smaller body, the bodies are a double planet system. The moon’s center of orbit is within the Earth.
  • When Pluto was still recognized as a planet, Pluto and Chadron were a double planet system.
  • Another rule suggested for distinguishing a moon-and-planet system from a double planet system is the path of the smaller body around the star. If the smaller object’s path around the larger object causes it sometimes to change direction relative to the star (retrograde motion), the smaller object is a moon. If the smaller object’s orbit around the star has no retrograde motion, then the two objects are a double planet system.
  • The Moon has no retrograde motion relative to the Sun. By the second rule listed above (and by some proposed ratios of relative mass), the Earth’s Moon is not a moon.

How many of these things did you already know? J.

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