The RTMC Astronomy Expo is one of the major gatherings of amateur astronomers in the United States.
Founded by Clifford W. Holmes and the Riverside Astronomical Society, the RTMC Astronomy Expo began in 1969 as the Riverside Telescope Makers Conference at Riverside City College in Riverside, California. It consisted of a series of lectures about astronomy and telescope making with a competition for quality and innovative telescopes. In 1973 it was moved to a dark-sky site near Idyllwild and in 1975 it was moved to its current home near Big Bear City. Previously, it was held on the three-day Memorial Day weekend. As of 2010, it is held in May on the weekend that corresponds with new moon to allow amateur astronomers the best viewing conditions.[1]
The organization annually presents the Clifford W. Holmes Award for "Major Contribution to Popularizing Astronomy, the Warren Estes Memorial Award for "Best Use of Simple Materials and Technique" in making telescopes, and the Clyde Tombaugh Award "Creative Innovation in Telescope Design".
To better reflect the evolution of amateur astronomy, the Riverside Telescope Makers Conference was renamed the RTMC Astronomy Expo in 2003. Each year the scope of activities continues to grow and evolve and has lectures, workshops, extensive beginners activities, a swap meet, astronomy clubs and other organizations, and vendors demonstrating and selling astronomical products. The Expo continues to promote family activities with swimming, canoeing, horseback riding, archery, wall climbing. Extensive hiking and mountain biking trails are also available.
In 2007, the Riverside Telescope Makers Conference, Inc. announced a fall event to be held in Pasadena named the Pacific Astronomy and Telescope Show (PATS). This annual event is held at the Pasadena Convention Center and focus displays by commercial vendors, astronomy clubs and other organizations as well as talks and workshops. The first PATS was held on September 13–14, 2008. It is designed to complement the ongoing RTMC Astronomy Expo which will continue to be held in Big Bear in May of each year.