3

In the Gregorian calendar, the current standard calendar in most of the world, most years that are multiples of 4 are leap years. In each leap year, the month of February has 29 days instead of 28. Adding an extra day to the calendar every four years compensates for the fact that a period of 365 days is shorter than a tropical year by almost 6 hours. This calendar was first used in 1582.

Some exceptions to this basic rule are required since the duration of a tropical year is slightly less than 365.25 days. Over a period of 4 centuries, the accumulated error of adding a leap day every 4 years amounts to about 3 extra days. The Gregorian calendar therefore removes three leap days every 400 years, which is the length of its leap cycle. This is done by removing February 29 in the three century years (multiples of 100) that cannot be exactly divided by 400.^[3] The years 2000 and 2400 are leap years, while 1800, 1900, 2100, 2200, 2300 and 2500 are common years. By this rule, the average number of days per year is 365 + ¹⁄₄ − ¹⁄₁₀₀ + ¹⁄₄₀₀ = 365.2425.^[4] The rule can be applied to years before the Gregorian reform (the proleptic Gregorian calendar), if astronomical year numbering is used.^[5]

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 leap year (also known as an intercalary year or a bissextile year) is a year containing one additional day (or, in the case of lunisolar calendars, a month) added to keep the calendar year synchronized with the astronomical or seasonal year.^[1] Because seasons and astronomical events do not repeat in a whole number of days, calendars that have the same number of days in each year drift over time with respect to the event that the year is supposed to track. By inserting (also called intercalating) an additional day or month into the year, the drift can be corrected. A year that is not a leap year is called a common year.

For example, in the Gregorian calendar, each leap year has 366 days instead of the usual 365, by extending February to 29 days rather than the common 28. Similarly, in the lunisolar Hebrew calendar, Adar Aleph, a 13th lunar month, is added seven times every 19 years to the twelve lunar months in its common years to keep its calendar year from drifting through the seasons. In the Baha'i Calendar, a leap day is added when needed to ensure that the following year begins on the vernal equinox.

The name "leap year" comes from the fact that while a fixed date in the Gregorian calendar normally advances one day of the week from one year to the next, the day of the week in the 12 months following the leap day (from March 1 through February 28 of the following year) will advance two days due to the extra day (thus "leaping over" one of the days in the week). For example, Christmas fell on Tuesday in 2001, Wednesday in 2002, and Thursday in 2003 but then "leapt" over Friday to fall on a Saturday in 2004.^[2]

The same type of problem happens in the relationship between the day and the number of seconds in the day: If you divide the larger measure of time by the smaller, you do not get a whole number. Instead, the result is an unending decimal. There is no way to perfectly fit a whole number of seconds into a day, nor is there a way to perfectly fit a whole number of days/months into a year. As leap years are used to correct calendar drift, the resulting drift in measuring the diurnal cycle is corrected by the use of leap seconds.

1

Regents of the University of California v. Bakke was a landmark Supreme Court decision in 1978 upholding affirmative action. It found diversity in the classroom to be a compelling state interestand allowed race to be one of several factors in college admission policy, but rejected specific quotas, such as the 16 out of 100 seats set aside for minority students by the UC Davis School of Medicine. Although the court had outlawed segregation in schools, it had not resolved the legality of voluntary affirmative action programs initiated by universities. Proponents deemed such programs necessary to make up for past discrimination, while opponents believed they violated the Equal Protection Clause of the Fourteenth Amendment. The case fractured the court: the nine justices issued a total of six opinions. The judgment of the court was written by Justice Lewis Powell, and two different blocs of four justices joined various parts of Powell's opinion. The decision had little practical effect on most affirmative action programs. In 2003 the court upheld Powell's position in a majority opinion in Grutter v. Bollinger. (Full article...)