Fact and Fancy

absolute magnitude actually Alpha Centauri Andromeda Andromeda galaxy apparent astronomers atmosphere atoms average billion bits body bright brighter built-in doubter captured carbon dioxide cent Cepheids circle close comet cometary planetoids concentration factor course Darwin decrease Delta Cephei diameter distance Earth Earth's center Earth's motion Earth's surface energy equal Equation escape velocity euphotic zone exist fact formed full Moon Galactic center Galaxy Galileo globular clusters gravitational force Greek hydrogen Ice Ages Jupiter Kapp land layer less light-years Magellanic Clouds Mars mass matter means measure mercury miles a second miles an hour miles/sec missile molecules Moon's move naked eye Neptune nova number of stars ocean orbit oxygen parallax parsecs particles Phobos phosphorus planetary planetoids Pluto Population reach reason satellite Saturn scientist seems seen Solar System space spaceship sphere supernova suppose telescope temperature Tenth Planet theory thing tion universe Uranus Venus visible weight