The Rescue Team's Moon Log: Moonrise and Eclipse Pairs

Night Drills in Port Alder

1The town of Port Alder, on a rocky coast in the Northern Hemisphere, has a volunteer sea rescue team. Before each storm season the team practices night searches on the beach, looking for a dummy "swimmer" with flashlights and radios. Eighth grader Teodoro Quillen joined the team's youth program this year. Team leader Ms. Ama Thorvaldsen asked him to keep a moon log for one month, because the Moon changes how dark the beach is at night.

2Teodoro checked the sky each evening and used a sky app for moonrise times. During that month, the Sun rose at about 6:40 AM and set at about 6:50 PM. Table 1 shows part of his log.

3At a team meeting, Ms. Thorvaldsen set up a model in a dark room. A bright lamp stood for the Sun, Teodoro's head stood for Earth, and a white foam ball on a stick stood for the Moon. Turning slowly in place stood for Earth's daily spin. Moving the ball around his head, counterclockwise as seen from above, stood for the Moon's orbit, which goes the same direction as Earth's spin and takes about 29.5 days from one new moon to the next. As the ball moved, Teodoro saw the lit part of it change shape.

4Teodoro also listed the eclipses of 2025 (Table 2). Then Ms. Thorvaldsen taped the ball to a hula hoop around Teodoro's head and tipped the hoop slightly, about 5°, the way the Moon's orbit is tipped compared with Earth's path around the Sun. With the hoop tipped, the ball usually passed a little above or below the shadow of Teodoro's head. Next, Teodoro carried the tipped hoop in a big circle around the lamp, keeping the tip pointed toward the same wall the whole time. Only at two spots on opposite sides of that circle did the ball pass straight through his head's shadow and, half a lap later, straight between his head and the lamp.