Astronomy

accurate Andromeda angle appear asteroids astronomer atoms axis bright brighter brightest calendar centre chromosphere circle clouds clusters colour comet constellations corona crater cycle dark density diameter disc distance dwarf Earth Earth's atmosphere Earth's orbit Earth's surface electrons elliptical energy Equator faculae fainter fixed stars Fraunhofer lines Galaxy giant globular clusters gravity Greek helium horizon hundred hydrogen ionised Jupiter known layer light light-years lines luminosity lunar magnitude main sequence Mars mass Mercury meteors miles Milky million minor planets Moon Moon's surface mountain move nebulae Neptune nucleus observed occur Orion parallax parsecs particles path period of rotation photographic photosphere planetary Pluto Pole position prominences proper motion protons radiation rays regions round the Sun Saturn seconds of arc seen shadow shown shows Sirius Solar System space spectra spectral types spectrum speed sphere stellar Sun's sunspots telescope temperature Uranus Venus visible wave-length