Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
William Kenneth Hartmann
open-in-new
<p>William Kenneth Hartmann (born June 6, 1939) is an American <a href="/facts/Planetary_science/ocX6rp0d">planetary scientist</a>, artist, author, and writer. He was the first to convince the scientific mainstream that the <a href="/facts/Giant_impact_hypothesis/x2cw2Xxn">Earth had once been hit by a planet sized body</a> (<a href="/facts/Theia_(planet)/wNcb6LB9">Theia</a>), creating both the <a href="/facts/Moon/zKHqEMPb">Moon</a> and the Earth's 23.5° tilt. </p>