LC ClassificationQB

17th century(296) asteroids(260) astrobiology(292) astrology(545) astrophysics(3,235) biography(3,730) biology(507) black holes(734) children(982) children's(1,308) cosmogony(94) cosmology(8,661) cosmos(416) Creation(246) dark matter(194) earth(1,858) education(309) educational(178) elementary(217) environment(261) evolution(491) exploration(409) Extraterrestrials(144) fall(851) galaxies(525) galaxy(180) Galileo(904) general relativity(134) general science(212) geography(786) geology(581) gravity(190) guide(288) history(6,869) history of science(2,880) informational(841) Jupiter(245) juvenile(420) juvenile non-fiction(266) kids(339) leaves(197) lunar(51) maps(262) Mars(977) Mars (Planet)(59) math(1,852) meteors(173) moon(1,842) nasa(388) natural science(713) nature(1,606) Newton(84) observation(158) outer space(1,121) philosophy of science(190) photographs(351) photography(720) physics/astronomy(118) picture book(2,410) planet(242) planetology(43) planets(4,565) Pluto(238) popular science(1,909) quantum mechanics(190) quantum physics(299) quasars(71) reference(2,600) relativity(394) Renaissance(308) science(45,216) science and technology(281) science nonfiction(271) scientists(363) solar system(4,587) space exploration(784) space flight(171) spacetime(112) spring(561) stars(3,306) string theory(294) summer(336) theoretical physics(159) time(2,342) universe(2,082) weather(982) winter(692)