Where were you on October 4, 1957? That’s the day, 50 years ago, when the Soviet Union launched Sputnik 1, the first artificial satellite. Even though they knew of the Soviets’ plans, American officials found themselves scrambling to track Earth’s new “moon.” A worldwide network of tracking cameras wasn’t ready yet, but dedicated teams of amateur astronomers — organized by the late Fred Whipple under Project Moonwatch — were.

To compute the satellite’s orbit, scientists needed to know where and when it crossed the sky from multiple locations. So each Moonwatch team created an “optical fence” along the celestial meridian, with up to a dozen observers using low-power, wide-field telescopes like the one shown here. At one point, the project had enlisted about 5,000 volunteers and 230 teams worldwide.

When the Moonwatch program finally ended in 1975, it still boasted more than 100 active teams. More importantly, the effort represented a unique collaboration uniting amateur and professional astronomers at the dawn of the Space Age. Christine Pulliam chronicles the program's success — and the initial opposition of some officials to using amateur volunteers — in the October 2007 issue of Sky & Telescope.

Did you participate in Project Moonwatch? Do you own one of these rugged little telescopes? If so, we'd like to hear from you. Send us your recollections and pictures, and we'll post them here. Some readers have already responded; their stories are on the next pages.