Triumph of Reason: Astronomy
  by Groff Schroeder

Thanks to public education, the average American who looks into the night sky knows a great deal about what he or she is seeing. Many people can easily identify the planet Venus (also known as the evening or morning star), which appears brightly on the horizon around sunset and sunrise, sometimes accompanied by the planet Mercury. Others can identify the red glow of Mars and know when and where to point their telescopes to observe the ringed planet Saturn.

Most of the twinkling white dots in the slowly rotating background are stars of our Milky Way galaxy. Stars are almost unimaginably massive spheres of fantastically hot gas, fueled by the fusion of hydrogen into helium. Other points of light we see as stars in the night sky are galaxies so far away that it impossible to distinguish their millions of individual stars from a single point of light. Scientists can even tell us that the closest star to our sun is about four light years away and that a light year is the distance light travels at 186,000 miles/second in one year.

To the earliest humans, the objects in the sky were unknown, and life on earth might have been a surreal mix of daily bounty and nightly terror. In the day, the rising sun provided light, warmth and assurance, peaking at noon at its highest point in the sky; but as the day wore on, night would approach - dark, cold, and full of uncertainty and danger.

It was probably easy for the earliest humans to discern the phases of the moon. However, at unexpected intervals, the moon could be full and friendly, then suddenly fade away in minutes as if being devoured by a giant mouth, slowly disappearing completely only to reappear a few minutes later. During an eclipse of the sun, it must have been quite terrifying to live in ignorance about the solar system. Early humans' actual interpretations of the night sky are lost to history, but given our current understanding of the universe, it is clear that at some point people began to study it.

Studying the moon's waxing into fullness and waning into darkness is one thing - determining when to migrate is another. On the survival scale, it probably did not matter if humans understood eclipses or phases of the moon, but if they failed to recognize seasonal changes, it could cost the group their lives when winter set in. Once humans figured out agriculture, it became important to determine when to plant crops. Since a shadow cast at noon is at its longest on the winter solstice and shortest on the summer solstice, early human astronomers may have figured out how to determine the longest and shortest days of the year quite quickly.

While early humans' interest in the solstices probably had eminently practical roots, today many religions celebrate important holidays in conjunction with the winter solstice, even though a correct reading of the salient religious texts may suggest that the celebrated events actually happened at some other time of year. Belief systems can adjust their customs and even their calendars to meet practical needs, but astronomy suggests that the movement of the planets and the stars remains immutable.

 

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