Solar calendar

A solar calendar is a calendar whose dates indicate the position of Earth on its revolution around the Sun or, equivalently, the apparent position of the sun moving on the celestial sphere. The other commonly used system is a lunar calendar which dates the months based on cycles of the lunar phases. The Gregorian calendar, widely accepted as standard in the world, is an example of solar calendar.

The natural science of astronomy is the study of celestial objects, observations and phenomena in the night sky. The ancient discipline of astronomy is the key method of calculating a date and time. A star in a solar system is the source of light which creates the stellar day, the rotation period of orbiting planets regulates the seasons on a planet surface, this combination is monitored and recorded by a calendar.

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.

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