PHILADELPHIA (Reuters Life!) - A three-foot telescope used by the Italian astronomer Galileo, whose discoveries revolutionized astronomy, is the main attraction at an exhibition at the Franklin Institute.

On its first trip outside of Italy, the 400-year-old telescope is one of only two instruments still known to exist that were used by Galileo to support the Copernican theory that the earth and the other planets revolved around the sun, and not vice versa.

“There will not be a second time in the States,” said Paolo Galluzzi, the director of the Instituto e Museo Nationale di Storia della Scienza in Florence, Italy, which loaned the telescope, said of the U.S. tour.

The exhibition, “Galileo, the Medici, and the Age of Astronomy,” which begins on Saturday and runs until September 7, is the opening event of the International Year of Astronomy, to mark the 400th anniversary of Galileo’s discoveries.

The 1610 telescope, tilted in its case at a sharp angle as if focused on the heavens, includes an inscription at one end in which Galileo recorded the instrument’s magnifying power of 20.

Following the Philadelphia show the exhibition will travel to Stockholm for about a week before returning to Florence.

Dennis Wint, president of the Franklin Institute, said the exhibition examines Galileo’s impact on science, the relationship between art and science in the renaissance of the Medici family, the relationship of Galileo to the church, and the relevance of the astronomer today.

“His achievement transformed the course of human history,” Wint told a news conference.

The exhibition also includes astronomical and mathematical instruments from the 16th century as well as contemporary scientific books, maps, and portraits of the Medici Dukes of Tuscany who ruled the Italian region from the 15th to the 18th centuries.

Galileo dedicated the book recording his discoveries to the Medici Duke Cosimo II, further boosting the family’s prestige and influence in the courts of Europe, according to the exhibition.

Many of the scientific instruments on display show the intersection of art and science, as championed by the Medici family. Among them is a brass level from 1560 with intricate inlaid patterning.

Galluzzi said Galileo used a telescope, not necessarily the one in the Philadelphia show, to identify the four moons of Jupiter on January 13, 1610.

“He was the first man who had the privilege of looking at this,” Galluzzi said. “I imagine his first reaction was thinking that Copernicus was right.”