The earliest humans viewed the night sky with awe and wonder, even as
we do today, and they must have had many questions. Why does the Moon
change shape nightly? How far away from us are the stars? What are those
points of light blazing across the heavens in numbers almost too vast to
comprehend? Why do the same patterns appear night after night, year after
year, generation after generation?
Almost four hundred years ago Galileo looked through his telescope
and saw things the eye alone could not detect. He observed mountains,
valleys, and craters on the seemingly smooth Moon.
He saw dark spots move across what was thought to be the featureless Sun.
He saw that "wandering stars" (planets, from the Greek word meaning wanderer)
were disks, not points of light.Saturn, he noted, had ear-like features at either side of the disk (telescopes would later reveal these as rings). Four dots were visible around Jupiter; they changed position hourly. Galileo decided they were satellites in orbit around the planet, that the Moon might similarly be in orbit around Earth, and Earth in orbit around the Sun. He watched Venus go through phases like those of the Moon and deduced that they were caused by the angle of the Sun's rays reflecting off that planet, as observed from Earth. He looked at the stars in the Orion constellation and where the unaided eye could see nine stars, he saw ten times that number.
Galileo made momentous discoveries with a telescope that enlarged
images about thirty times. Telescopes
today are far more powerful; they permit us to gather hundreds of
thousands of times more light than Galileo's telescopes.Scientists now perceive a Universe that is vastly larger and far more complex than Galileo or his contemporaries could have imagined, and they are studying it with far larger and more complex instruments.
No longer do professional astronomers look through their telescopes; they use them instead as giant cameras to gather images electronically. Sophisticated instruments permit them to study light from unimaginably distant objects.
Astrophysical research increases our knowledge of the nature and content
of the Universe. Our Sun, the closest star to Earth,
is some 300,000 times closer than any other star. It is but one
of approximately 100 billion stars in
a great flattened disk of stars, interstellar dust, and glowing nebulae that we
call the Milky Way Galaxy. The Milky Way Galaxy is only one of
approximately 100 billion galaxies; astronomers can see distant
galaxies essentially everywhere they aim their telescopes. For close to a century, astronomers at Yerkes have added substantially to our understanding of the Universe. They began taking photographs with the 40-inch Refractor in 1900; since then, they have accumulated tens of thousands of photographic negatives of galaxies, stars, planets, comets, the Sun, and the Moon. These negatives constitute a valuable archival research facility.
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