PASSAGE 35

　　The observation of the skies has played a special part in the lives and cultures of peoples since the earliest of times. Evidence obtained from a site known as the Hole in the Rock, in Papago Park in Phoenix, Arizona, indicates that it might have been used as an observatory by a prehistoric people known as the Hohokam.

　　The physical attributes of the site allow its use as a natural calendar/clock. The hole at Hole in the Rock is formed by two large overhanging rocks coming together at a point, creating a shelter with an opening large enough for several persons to pass through. The northeast-facing overhang has a smaller opening in its roof. It is this smaller hole that produces the attributes that may have been used as a calendar/clock.

　　Because of its location in the shelter's roof, a beam of sunlight can pass through this second hole and cast a spot onto the shelter's wall and floor. This spot of light travels from west to east as the sun moves across the sky. It also moves from north to south and back again as the Earth travels around the Sun, the west-to-east movement could have been used to establish a daily clock, much like a sundial, while the north-to-south movement could have been used to establish a seasonal calendar.

　　The spot first appears and starts down the surface of the wall of the shelter at different times of the morning depending on the time of the year. The spot grows in size from its first appearance until its maximum size is achieved roughly at midday. It then continues its downward movement until it reaches a point where it jumps to the floor of the shelter. As the Sun continues to move to the west, the spot continues to move across the shelter floor and down the butte, or hill, toward a group of small boulders. If a person is seated on a certain one of these rocks as the spot reaches it, the Sun can be viewed through the calendar hole. This occurs at different times in the afternoon depending on the time of year.

　　1. What does the passage mainly discuss?

　　(A) observations of the stars by ancient people

　　(B) rock formations of Arizona

　　(C) a site used by ancient people to measure time

　　(D) the movement of the earth around the Sun

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