History of astronomy

Astronomy is the branch of physics that studies celestial bodies and the universe as a whole.

From this perspective, the study of celestial bodies can be reasonably said to have begun when at some point humanity looked up and began to observe the moon and the stars and the planets regardless of how they may have thought of them.

These ancient beginnings are often indicated by structures studied by archeologist. Stonehenge, constructed sometime between 3100 to 2000 BC may have constituted an astronomical site, possibly an observatory or the structrue may have been designed upon observations previously made. Either way, it seems clear that Stonehenge was meant to take advantage of astronomical phenomena since the "heelstone" in the circle of stones is aligned with the rising Sun on Midsummer's Day (June 21, the Summer Solstice). This represents a true astronomical alignment. Many other Megalithic sites also demonstrate such alignments.

The Megalithic Passage Tomb at Newgrange, built about 3200 BC.also demonstrates knowledge of astronomical phenomena. The passage and single chamber of the tomb are illuminated by a shaft of sunlighthe that shines through the roof box over the entrance and penetrates the passage, lighting up the chamber at winter solstice sunrise. This happens at dawn from the 19th to the 23rd of December for 17 minutes.

Earlier evidence of astronomical observations can be found in Vedic India in the Rg Veda which contains a verse observing the winter solstice in the constellation Aries. This would have placed it at around 6500 BC. The Myth of Janus, a four headed god of of the Vedic people of India, presents the possibility of astronomical observations around 4,000 BC. Each head of Janus represented a phase of the moon which in turn represented one of the four seasons: one full moon represented the spring equinox, one full moon represented the autumn equinox, the waning moon the winter solstice and a waxing moon representing the summer solstice.This dating is disputed but it does indicate a very early study of both the contellations and the moon.

Halley's Comet (considered a guest star) was noted by Chinese astronomers as early as 240 BC and perhaps as early as 1059 BC.