in the years after a volcanic eruption are caused by sulphate aerosols, rather than volcanic dust. In 1949 the family relocated to Yerkes Observatory in Wisconsin, then in 1955 to Phoenix, Arizona while Aden established the new Kitt Peak National Observatory, and then in 1961 to Tucson where Aden began working at the University of Arizona. In 1970 Aden took a sabbatical so the couple could spend their time exploring barriers to the uptake of solar energy technology. In 1972, Meinel returned to academic employment, working as a research associate at the University of Arizona Optical Sciences Centre, which Aden had founded in 1964. The Meinels continued their solar research throughout the 1970s as part of a team at the university and experimented in developing prototype solar collectors. The Meinels became prominent advocates of solar thermal energy nationally. They were skeptical of the existing focus on small scale solutions, instead arguing for large-scale applications of solar technology by industry and government. They viewed the barriers as chiefly economic, rather than technical. They believed that through large-scale applications the costs and barriers for small-scale applications would reduce and the technology would become more affordable for developing countries. One idea they developed and promoted was the construction of a 5000-square mile farm of parabolic solar collectors in the deserts of Arizona and New Mexico to heat water to produce 1000-gigawatts of electricity using steam turbines. They also explored other alternative energy sources, such as cultivating the tumbleweed kali tragus as a biofuel. Together they wrote two books on the subject of solar energy, Power for the People (1971) and the textbook Applied Solar Energy (1976). Meinel was a member of the Arizona Solar Energy Commission and of the Solar Energy Panel of the U.S. Congress Office of Technical Assessment. However, by 1977 the Meinels had become despondent towards the prospects of solar energy, with Meinel telling Congress "reality has dawned as the magnitude of the economic barrier has become clear [...] solar energy is expensive and is undependable." Solar energy research and development funding also began to dry up and the Meinels returned to focusing on astronomy. In 1983 Meinel co-authored with Aden the book Sunsets, Twilights, and Evening Stars on the various optical phenomena visible from sunset, including their observations of the optical effects of volcanic eruptions. In 1984 Meinel and Aden were recruited by the Jet Propulsion Laboratory (JPL) in