A telescope to the past.

Four hundred years ago, Galileo Galilei built his first telescope--and began to change the way people viewed the universe. In honor of the anniversary, one of Galileo's telescopes [shown above] is on display at the Franklin Institute in Philadelphia through the summer, (It's one of two that still exist; until now, neither had been outside Italy since Galileo's lifetime.) An astronomer and physicist, Galileo made his first telescope in 1609 after hearing that a Dutch eyeglass maker had built a spyglass. Galileo's telescopes allowed him to become the first to see mountains on the moon and satellites orbiting Jupiter. These discoveries challenged the Earth-centered view of the universe that had prevailed for a thousand years. In 1633, Galileo was put on trial by the Roman Catholic Church for promoting the Copernican theory that the Earth and other planets orbited the sun. He was convicted of holding views "contrary to Scripture" and declared "vehemently suspect of heresy." Galileo recanted and spent the rest of his life under house arrest.

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