Apollo and Adonis and Helios were Greek gods of the Sun
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Apollo and Adonis and Helios were Greek gods of the Sun, all borrowed from older civilizations which had been content to venerate, and to calculate only when necessity demanded. But the Greeks loved knowledge for its own sake. Soon they were poking their inquisitive minds into the nature and movements of their deity. How far was the Sun from the Earth? What distance stretched between the Sun and Moon?
From observation they knew that the two heavenly bodies subtended almost the same angle; they could see that the diameters appeared equal, yet at eclipses the Sun always passed behind the Moon; it must be the farther and the larger of the two. If only some wise astronomer could reckon the number of miles intervening, then they could easily calculate the relative sizes, and set a scale for all astronomical measurement.
About 270 B. C. Aristarchus of Samos had a bright idea. When the Moon is exactly at first or last quarter the angle at the Moon between the Sun and Earth is a right angle. If he could measure the angle which they subtended at that moment on Earth, he could compute their relative sizes and distances. His method was perfectly correct, but unfortunately he had chosen an extremely difficult thing to measure. A very slight error in observation would multiply many times in his results. He found that the Sun was twenty times as far from Earth as the Moon. Had he said four hundred times, he would have been more nearly correct.
After Aristarchus the problem was neglected until 1672. Then, when Mars was favorably situated in opposition to the Sun, astronomers made another attempt. They were rather more successful than their predecessor, but there were still a good many miles lacking in their results. During the eighteenth and nineteenth centuries, astronomers tried again and again to solve the problem by measuring the distance during transits of Venus, and by employing the aid of a few minor planets which come nearer the Earth than any body except the Moon. This method was more successful, and the observers were better equipped. Nearly 93,000,000 miles is generally accepted today as the average distance between Sun and Earth.
Greek tradition measured angles and tried to ascertain proportions; but optical instruments, which enable us to study the nature of the Sun itself, are quite accidentally due to the Persian love of fire.
About 1000 B. C. there lived in the mountains east of the Tigris, a great leader who organized the fire worship of his community into an energetic and powerful religion. He was an abstract thinker and never confounded fire with God. But he did equate evil with darkness, and goodness with light, taking the Sun for his symbol, and calling his god Mazda, the name by which we know a type of electric lamp used today. Very little of Zoroaster's personal history is recorded, but the doctrine he taught went striding down into Roman times when it influenced early Christianity. By another route it traveled into Mecca where it became the foundation of Mohammedanism. Early in the thirteenth century A. D., when these two strands of Sun worship met in Europe, they resulted in an investigation of light. Physics and chemistry were things of the Devil, but optics belonged to theology. By 1250 Roger Bacon was experimenting with prisms and lenses, paving the way for the invention of eyeglasses, telescopes and all the other instruments used to study the Sun. When the Renaissance began to resurrect more mundane sciences, astronomy had flourished for over two hundred years.
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