Kepler's laws of planetary motion law" is what became the Second Law in the set of three; but Kepler did himself not privilege it in that way. Johannes Kepler published his first two laws about planetary motion in 1609, having found them by analyzing the astronomical observations of Tycho Brahe. Kepler's third law was published in 1619. Kepler had believed in the Copernican model of the solar system, which called for circular orbits, but he could not reconcile Brahe's highly precise observations with a circular fit to Mars' orbit—Mars coincidentally having the highest eccentricity of all planets except Mercury. His first law reflected this discovery.
Association of Lunar and Planetary Observers Association of Lunar and Planetary Observers The Association of Lunar and Planetary Observers (ALPO or A.L.P.O.) is an international scientific and educational organization established in March, 1947 in the United States by Walter H. Haas, and later incorporated in 1990. ALPO is an organization for advancing and conducting astronomical work by both professional and amateur astronomers who share an interest in solar system observations. It is currently headquartered in Springfield, Illinois. ALPO studies solar system objects such as the Sun, the Earth's Moon, planets, asteroids, meteors, and comets. ALPO stimulates, coordinates, and generally promotes the study of these bodies using