The transit of Venus happens every 100 years. The last one was in June 2012, and the next one occurs in 2117. This happens as Venus directly passes between the Earth and the Sun. This once-in-a-lifetime astronomical alignment has been witnessed eight times since the telescope was invented. These eye-witness-accounts occurred in 1631, 1639, 1761, 1769, 1874, 1882 and 2004, and the last was in June 2012.Continue Reading
The one-hundred-year pair-pattern for the transit of Venus is due to the orbital nodes of Earth and Venus. Since these orbital nodes are changing, transits which used to occur in May and November are now happening in June and December. Fred Espenak of NASA has released a Six Millennium Catalog of Venus Transits; and, it contains predictions based on geocentric calculations.
The transit of Venus has helped astronomers calculate Earth's distance from the Sun: It is calculated using the astronomical unit or AU. This transit was proposed by English astronomer Edward Halley in 1716. Scientists continue to study transits to this day, to discover extrasolar planets and exoplanets beyond the solar system. The Kepler Mission was launched by NASA in 2009 to find exoplanets; and, some are equal to the size of the Earth.Learn more about Time & Calendars
Calendar dates repeat regularly every 28 years, but they also repeat at 5-year and 6-year intervals, depending on when a leap year occurs within those cycles, according to an article from the Sydney Observatory. Repeating calendar dates are also affected by the adjustments made for leap years at the end of each century.Full Answer >
The latest atomic clock developed by the National Institute of Standard and Technology and the University of Colorado at Boulder is accurate to within one second per 15 billion years, as of April 2015. This accuracy level is three times more accurate than the previous strontium clock developed in 2014.Full Answer >
Although astronomers and geologists use the word "eon" to mean 1 billion years, it is more commonly used to refer to any long, indefinite period of time. Like the words "age," "epoch" and "era," it does not refer to a set number of years.Full Answer >
The Gregorian calendar was calculated to be 52 weeks long after German astronomer Christopher Clavius proposed that leap years should be counted only if the digits of years ending in 00 were divisible by 400. The Gregorian calendar is based on the Roman Julian calendar.Full Answer >