Physics - From Stargazers to Starships

360 degrees accurate actually Alex Zaliznyak Alexandria ancient angle Apollo Aristarchus astronomers Big Dipper calculation calendar CC-BY-SA celestial pole celestial sphere chapter Estimating circle clock close Columbus constellation coordinates craters cross-staff David Stern December 21 diameter direction drawing Earth Earth's axis Earth's rotation east equator equinox Eratosthenes Estimating the Distance exactly Figure FlexBook on www.ck12.org gnomon gravity Greek Greenwich half heat heavens Hellespont hemisphere Hipparchus horizon ice ages June 21 Jupiter later latitude longitude lunar eclipse Lunokhod marked Maya Maya Calendar measured Mercury meridian Milankovich month Moon moon's orbit motion moved Navigation night noon noontime Sun north pole northern observed opposite parallax perpendicular planets Polaris pole star Posidonius position precession Ptolemy Public Domain radius satellite seasons solar solstice Stargazers to Starships Starships FlexBook summer Sun's path sundial sunlight sunrise sunset telescope Venus visible width winter zenith zodiac