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The position of the Sun in the sky is a function of both the time and the geographic location of observation on Earth's surface. As Earth orbits the Sun over the course of a year , the Sun appears to move with respect to the fixed stars on the celestial sphere , along a circular path called the ecliptic .
Tun Sun remained independent until it was seized and became a vassal of Funan in the 3rd century CE, [4]: 20 [2]: 258 at least before 245 CE. [4]: 25 Tun Sun disappeared from history about the beginning of the 6th century CE, [2]: 262 when new principalities of Dvaravati emerged in central Thailand. [7]: 234 [8]
If the position of the Earth in its orbit around the Sun is reckoned with respect to the Equinox, the point at which the orbit crosses the celestial equator, then its dates accurately indicate the seasons, that is, they are synchronized with the declination of the Sun. Such a calendar is called a tropical solar calendar [citation needed].
A panel from a typical calendar, showing the month of August 2004 (B.E. 2547). Lunar dates are also provided. The Thai solar calendar (Thai: ปฏิทินสุริยคติไทย, RTGS: patithin suriyakhati thai, "solar calendar") was adopted by King Chulalongkorn (Rama V) in 1888 CE as the Siamese version of the Gregorian calendar, replacing the Thai lunar calendar as the legal ...
[11]: 70 It derives from the movement of the sun from one position to another in the zodiac. According to its literal meaning in Sanskrit, a Songkran occurs every month. However, the period that Thai people refer to as Songkran happens when the sun moves from Pisces to Aries in the zodiac. [12]
In ancient times, the sun's entry into Aries coincided with the equinox. However, due to the earth's axial precession, the sidereal year is slightly longer than the tropical year, causing the dates to gradually drift apart. Today, the sun's entry into Aries occurs around 18 April, according to astronomical definitions. [1]
The solar azimuth angle is the azimuth (horizontal angle with respect to north) of the Sun's position. [1] [2] [3] This horizontal coordinate defines the Sun's relative direction along the local horizon, whereas the solar zenith angle (or its complementary angle solar elevation) defines the Sun's apparent altitude.
Solar cycles are nearly periodic 11-year changes in the Sun's activity that are based on the number of sunspots present on the Sun's surface. The first solar cycle conventionally is said to have started in 1755. The source data are the revised International Sunspot Numbers (ISN v2.0), as available at SILSO. [1]