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The NASA website hosts a large number of images from the Soviet/Russian space agency, and other non-American space agencies. These are not necessarily in the public domain. Materials based on Hubble Space Telescope data may be copyrighted if they are not explicitly produced by the STScI . [1]
A lunisolar calendar was found at Warren Field in Scotland and has been dated to c. 8000 BC, during the Mesolithic period. [2] [3] Some scholars argue for lunar calendars still earlier—Rappenglück in the marks on a c. 17,000 year-old cave painting at Lascaux and Marshack in the marks on a c. 27,000 year-old bone baton—but their findings remain controversial.
The fact, however, that a year of twelve lunar months is ten or eleven days shorter than the solar year means that a lunar calendar drifts out of step with the seasons. Lunisolar calendars resolve this issue with a year of thirteen lunar months every few years, or by restarting the count at the first new (or full) moon after the winter solstice.
In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. Animation of the Moon as it cycles through its phases, as seen from the Northern Hemisphere. The apparent wobbling of the Moon is known as libration.
Lunar phase (illustration as seen from northern hemisphere) Moonrise [a] Culmination time (highest point) Moonset Best seen New moon: 6 AM Noon 6 PM Not visible unless there is a solar eclipse: Waxing crescent 9 AM Afternoon 9 PM Late morning to early evening First quarter 12 PM Sunset 12 AM Early evening to late night Waxing gibbous 3 PM
Using these whole numbers facilitates the construction of a lunisolar calendar. A tropical year (about 365.24 days) is longer than 12 lunar months (about 354.36 days) and shorter than 13 of them (about 383.90 days). In a Metonic calendar (a type of lunisolar calendar), there are twelve years of 12 lunar months and seven years of 13 lunar months.
This lunar timekeeping gave rise to the historically dominant, but varied, lunisolar calendars. The 7th-century Islamic calendar is an example of a purely lunar calendar, where months are traditionally determined by the visual sighting of the hilal, or earliest crescent moon, over the horizon. [332]
A lunisolar calendar is a calendar in many cultures, incorporating lunar calendars and solar calendars. The date of lunisolar calendars therefore indicates both the Moon phase and the time of the solar year , that is the position of the Sun in the Earth's sky .
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