... Help NASA Classify Martian Craters . ... The large Martian crater above just left of center: is this a fresh crater, a degraded crater, or a ghost crater? ... Tycho Brahe Measures the Sky . ... Brahe, who lived between 1546 and 1601, set out to solve the day's most pressing astronomical problem: to determine whether the Earth or the Sun was at the center of the Solar System. ... Second Millennium, Last Eclipse . ... Third Millennium, First Eclipse . ... The Millennium that Defined Earth . ...