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(Click for frequent words.) 84 telescopes 73 Telescope 72 optical telescope 72 observatory 68 infrared telescope 66 orbiting telescope 66 optical telescopes 66 Hubble 65 Hubble Space Telescope 65 Keck telescopes 64 observatories 64 orbiting Hubble Space Telescope 63 astronomers 63 Keck telescope 63 infrared telescopes 63 radiotelescope 63 inch refractor telescope 63 orbiting observatory 62 Very Large Telescope 62 refracting telescope 62 Hubble telescope 62 ESO VLT 62 Telescope LSST 61 Arecibo Observatory 61 adaptive optics 61 astronomical telescope 61 reflector telescope 60 hexagonal mirrors 60 infrared observatory 60 Arecibo telescope 60 Keck Telescopes 60 inch refractor 60 inch Schmidt Cassegrain 60 X ray observatory 60 Gemini telescopes 60 astronomical telescopes 60 spectrograph 59 robotic telescopes 59 interferometer 59 Hubble Telescope 59 aperture telescope 59 Space Telescope 59 astronomy 59 X ray telescopes 59 Herschel telescope 59 spectrometer 59 Keck Telescope 59 Keck Observatory 59 spacecraft 59 observatory telescope 59 Array ALMA 58 Submillimeter Array 58 Fermi telescope 58 Pan STARRS 58 XMM Newton 58 Telescopes 58 Atacama Large Millimeter Array 58 Subaru Telescope 58 Lunar Reconnaissance Orbiter LRO 58 WM Keck Observatory 58 JWST 58 COROT 58 Explorer WISE 58 HiRISE camera 58 Subaru telescope 58 astronomer 58 LOFAR 57 VLBA 57 SIRTF 57 Comet Lulin 57 inch Samuel Oschin 57 X ray telescope 57 Dobsonian telescope 57 Hubble Space Telescope HST 57 Nasa spacecraft 57 Large Binocular Telescope 57 Cerro Paranal 57 ESO Very Large Telescope 57 Cosmic Origins Spectrograph 57 submillimetre 57 ultraviolet spectrograph 57 ESO Paranal Observatory 57 particle detector 57 steering wheel tilts 57 Palomar Observatory 57 infrared astronomy 57 meter Keck telescopes 57 HiRISE 57 Steward Observatory 56 satellites 56 inch refracting telescope 56 planetary Transits 56 exoplanetary 56 planetarium 56 UKIRT 56 X ray observatories 56 LROC 56 Infrared Telescope Facility 56 Large Synoptic Survey 56 e MERLIN 56 AKARI 56 Observatory SDO 56 Galileo spacecraft 56 refractor telescope 56 Evolution Explorer 56 DEIMOS 56 Chajnantor plateau 56 ESO telescope 56 TSN PZ camera 56 optical infrared telescope 56 Arecibo radio 56 microshutters 56 Spitzer Space Telescope 56 orbiting 55 amateur astronomers 55 Ritchey Chrétien 55 WISE infrared 55 Keck Interferometer 55 Mauna Kea Hawaii 55 Cerro Pachón 55 celestial observations 55 gamma ray observatory 55 astronomical observatory 55 NIRSpec 55 Faulkes Telescope 55 telescope atop Mauna 55 Herschel Space 55 NASA Far Ultraviolet 55 astronomical observations 55 Planck satellite 55 Very Large Array 55 celestial object 55 LIGO 55 detect gravitational waves 55 Interferometer VLTI 55 WFC3 55 Near Infrared Camera 55 IBEX spacecraft 55 orbiting telescopes 55 Fomalhaut b 55 Spectrograph 55 imaging spectrometer 54 astronomy observatory 54 Extremely Large Telescope 54 Cassini 54 Kepler spacecraft 54 photometer 54 Kitt Peak 54 Astronomy 54 WMAP satellite 54 submillimeter wavelengths 54 Cerro Pachon 54 spectrographs 54 GALEX 54 IceCube 54 Wilkinson Microwave Anisotropy Probe 54 MeerKAT 54 orbiting gamma ray 54 gaseous planet 54 Gran Telescopio Canarias 54 stargazer 54 microlensing 54 Paranal Chile 54 APXS 54 NuSTAR 54 steerable radio 54 Solar TErrestrial RElations Observatory 54 Convection Rotation 54 Observatory telescope 54 fainter objects 54 NanoSail D 54 amateur astronomer 54 Andromeda galaxy 54 RXTE 54 orbiting observatories 54 coronagraph 54 Amateur astronomers 53 NASAs 53 La Silla Observatory 53 comet 53 ESA XMM Newton 53 Epsilon Aurigae 53 atop Mauna Kea 53 orbiting Saturn 53 LORRI 53 Terrestrial Planet Finder 53 retroreflector 53 quasars 53 interplanetary spacecraft 53 APEX telescope 53 Large Telescope 53 VISTA telescope 53 NASA STEREO 53 orbiting spacecraft 53 NASA Infrared Telescope 53 Burst Alert 53 distant galaxy 53 Mars Reconnaissance Orbiter 53 STIS 53 robotic spacecraft 53 Laser Interferometer Gravitational Wave 53 E ELT 53 Cassini Huygens 53 infrared 53 Spitzer infrared 53 Orbiter LRO 53 WIYN 53 CoRoT satellite 53 SkyCenter 53 astronomical observatories 53 SIM PlanetQuest 53 Solar Dynamics Observatory 53 gamma ray burst 53 extrasolar planet 53 SKA telescope 52 astronomical objects 52 Muchachos Observatory 52 Comet Holmes 52 HD#b 52 radiometers 52 Square Kilometre Array 52 hubble 52 slender crescent 52 Lowell Observatory 52 Hobby Eberly 52 parabolic antenna 52 Lick Observatory 52 ESO La Silla 52 MMT Observatory 52 Nasa Kepler 52 eyepiece 52 CSIRO Parkes radio 52 spectroscopic observations 52 Observatory Very 52 STEREO spacecraft 52 Hobby Eberly Telescope 52 extrasolar planets 52 Observatory 52 Galaxy Evolution 52 occultations 52 Cryosat 52 MARSIS 52 Global Surveyor 52 Infrared Telescope 52 GLAST 52 THEMIS satellites 52 portable planetarium 52 Saturn Cassini 52 STEREO mission 52 Comet Machholz 52 orbiting Chandra 52 spiral galaxy Messier 52 Webb Telescope 52 Arecibo radar 52 Rosetta orbiter 52 Mars Reconnaissance Orbiter MRO 52 Sombrero Galaxy 52 cosmic ray 52 Observatory STEREO 52 Earthlike planets 52 WISE telescope 52 Gemini Observatory 52 Ulysses spacecraft 52 Herschel Space Telescope 52 supergiant star 52 Chilean Atacama Desert 52 infrared wavelengths 52 Paranal 52 radial velocity 52 distant galaxies 52 SOAR telescope 52 New Horizons spacecraft 52 Ultraviolet Optical Telescope 52 Thirty Meter Telescope 52 Canary Telescope 52 Anisotropy Probe WMAP 52 Cassegrain telescope 52 Observatories 52 NASA Chandra 52 eyepiece #/#s f/#.# 52 Astronomers 52 neutrino detector 52 NASA Cassini spacecraft 52 HARPS spectrograph 52 gamma ray detector 52 BepiColombo 52 infrared spectrograph 52 Orion Nebula 52 RHESSI 52 Atacama Large Millimeter submillimeter 52 X ray Observatory 51 Adaptive Optics 51 Lovell Telescope 51 LSST 51 Southern Observatory ESO 51 Huygens 51 Helios 2B 51 astrophotographer 51 cosmic microwave radiation 51 Gemini Telescope 51 spiral galaxy NGC 51 ESA Planck 51 Giant Magellan Telescope 51 Suzaku X ray 51 Field Planetary Camera 51 Pan STARRS telescope 51 Faint Object 51 Cosmic Origins Spectrograph COS 51 CALIPSO 51 Astrophysical Research 51 gravitational wave 51 distant quasar 51 Spacewatch 51 earthshine 51 revolutionized astronomy 51 astrophotography 51 Large Binocular Telescope LBT 51 submillimeter wavelength 51 Proxima Centauri 51 astrometry 51 Las Campanas Observatory 51 ray Space Telescope 51 SDSS telescope 51 Ritchey Chretien 51 Adaptive optics 51 Field Imager 51 Earth orbiting satellites 51 orbiter 51 panoramic camera 51 infrared imager 51 origins spectrograph 51 robotic rovers 51 ESO telescopes 51 Solar Observatory 51 gravitational lenses 51 ATST 51 NASA Gamma ray 51 Gravity Probe B 51 VIRTIS 51 HiRISE camera aboard 51 ESA Herschel 51 Galileoscope 51 ROSAT 51 Jodrell Bank Observatory 51 binocular telescope 51 ASKAP 51 Schmidt Cassegrain telescope 51 Cassini Huygens spacecraft 51 NASA Kepler 51 spacecraft Cassini 51 Advanced LIGO 51 Square Kilometer Array 51 Multi Object Spectrograph 51 SOHO spacecraft 51 Cassini flyby 51 Orbiter MRO 51 Huygens lander 51 starshade 51 Anisotropy Probe 51 Cosmic Background Explorer 51 Solar Orbiter 51 submillimetre wavelengths 51 infrared camera 51 exoplanet 50 Webb Space Telescope 50 FORCAST 50 spectrometers 50 spectrographic 50 Mossbauer spectrometer 50 MARSIS radar 50 NASA MESSENGER spacecraft 50 Quadrantid meteor shower 50 planetarium projector 50 Kepler Mission 50 twin Keck telescopes 50 Reconnaissance Orbiter 50 asteroid Vesta 50 meter Keck telescope 50 Telescope BAT 50 Rosetta spacecraft 50 satellites orbiting Earth 50 THEMIS 50 Nikon D# Kowa 50 distant galaxy clusters 50 Gravitational lensing 50 interferometers 50 Mastcam 50 Schmidt Cassegrain 50 NOAO 50 solar corona 50 WIYN Observatory 50 Saturn rings 50 telescopic camera 50 telescopic observations 50 Wolszczan 50 NASA Wilkinson Microwave 50 comet Hale Bopp 50 Astrosat 50 Dobsonian 50 Long Wavelength Array 50 field Infrared Survey 50 Planetary Transits 50 Comet Hartley 2 50 optical wavelengths 50 Imaging Spectrograph 50 transiting planet 50 X ray wavelengths 50 distant supernovae 50 HARPS instrument 50 gamma ray telescope 50 SINFONI 50 impactor 50 Great Observatories 50 celestial objects 50 Interferometer 50 GRB #B 50 microlensing events 50 Surveys ACS 50 orbiting Hubble telescope 50 CubeSat 50 Andromeda Galaxy 50 HiRISE image 50 flyby spacecraft 50 gamma ray detectors 50 Area Telescope LAT 50 probe Huygens 50 exoplanet orbiting 50 Geminga 50 SMOS 50 Siding Spring 50 LCLS 50 Zeiss projector 50 gamma ray bursts 50 polarimetry 50 eyepieces 50 satellite 49 astrophysical phenomena 49 AU Mic 49 Samuel Oschin Telescope 49 WISE spacecraft 49 Caltech Palomar Observatory 49 Dalcanton 49 GJ #b [002] 49 Cassini spacecraft 49 Ring Nebula 49 imager 49 multiband imaging photometer 49 Mini TES 49 Solar System 49 NASA THEMIS 49 Infrared Array Camera 49 gravitational lens 49 Mars rover 49 MESSENGER 49 mySKY 49 Astronomical Observatory 49 Voorwerp 49 Context Camera 49 Herschel Planck 49 X ray Telescope XRT 49 Mount Stromlo Observatory 49 NEOWISE 49 astrometric 49 La Silla observatory 49 Landsat satellite 49 HIRES spectrometer 49 Kibo module 49 WFPC2 49 earthlike planets 49 Hawaii Mauna Kea 49 Delta Cephei 49 particle detectors 49 EarthScope 49 D CIXS 49 Herschel 49 ChemCam 49 unmanned spacecraft 49 WMAP 49 HARPS spectrograph attached 49 distant quasars 49 seismometers 49 cosmic ray detector 49 Werthimer 49 NASA Goddard 49 extrasolar 49 nanosatellite 49 VLBI 49 infrared detectors 49 spacecraft orbiting 49 extrasolar planets orbiting 49 HD #b [001] 49 Radio Astronomy Observatory 49 Kitt Peak Observatory 49 celestial sphere 49 Voyager spacecraft 49 Ultraviolet Imaging Spectrograph 49 exoplanet hunter 49 Pancam 49 flyby Cassini 49 Heliospheric Observatory SOHO 49 EVLA 49 UVOT 49 Epsilon Eridani 49 LRO 49 planets orbiting 49 Horizons spacecraft 49 orbiting satellites 49 spectroscopic 49 gigapixel camera 49 RAS Observatory 49 Solar Dynamics 49 comet nucleus 49 ESA Integral 49 planet orbiting 49 HD #b [002] 49 geostationary satellite 49 Thermal Emission Spectrometer 49 lander 49 GPS satellites 49 NASA Stratospheric Observatory 49 submillimeter 49 SSETI Express 49 Infrared Astronomical Satellite 49 Jodrell Bank 49 Mössbauer 49 electron microscope 49 highly elliptical orbit 49 spaceborne 49 Eta Carinae 49 radiometer 49 Sojourner rover 49 Space Telescope GLAST 49 Skynet 5C 49 Telescope Array 49 Planetary Camera 2 49 remote sensing satellites 49 Deep Impact comet 49 rover 49 Advanced Camera 49 Spitzer infrared spectrograph 49 radar altimeter 49 Comet NEAT 48 Giove B 48 moon Ganymede 48 Pleiades cluster 48 constellation Hercules 48 Hubble observations 48 seismometer 48 CloudSat 48 extrasolar planetary systems 48 Triangulum Galaxy 48 Hubble Space 48 Mars orbiter 48 Edwin Hubble 48 Paranal Observatory 48 XMM Newton satellite 48 laser altimeter 48 optical microscope 48 spectroscope 48 STScI 48 Spectrometer 48 orbital observatory 48 seismographs 48 Charon Pluto 48 quasar 48 James Fanson 48 Omega Centauri 48 Newtonian telescope 48 Hobby Eberly telescope 48 NASA Great Observatories 48 Titan flyby 48 UCO Lick 48 exo planet 48 Mini Thermal Emission 48 polarimeter 48 flyby 48 Kuiper belt object 48 Carnegie Observatories 48 waning gibbous 48 curved mirrors 48 Relations Observatory STEREO 48 comet Lulin 48 gravitational microlensing 48 Kuiper Belt object 48 telescopes astronomers 48 NASA Interstellar Boundary 48 Optical Gravitational Lensing Experiment 48 Cerro Tololo 48 NASA Cassini 48 exoplanets orbiting 48 Martian crater 48 bolometer 48 gamma ray telescopes 48 planetary missions 48 orbiting Mars 48 robotic explorer 48 EPOXI mission 48 Milky Way Galaxy 48 scatterometer 48 arcminutes 48 lunar orbiter 48 Comet McNaught 48 cryo electron microscope 48 Cygnus Lyra region 48 solar arrays 48 NRAO 48 GROND 48 spectroscopic measurements 48 Kepler telescope 48 Multi Object Spectrometer 48 Galilean moons 48 Astrophysicists 48 HUDF 48 DISR 48 asteroid 48 Space Telescope Imaging Spectrograph 48 HESS telescopes 48 Infrared Telescope UKIRT 48 Solar Terrestrial Relations 48 HD# [002] 48 galaxy M# [001] 48 moon Charon 48 KBOs 48 Mars Odyssey spacecraft 48 Mars Color Imager 48 Upsilon Andromedae 48 MESSENGER spacecraft 48 transmission electron microscope 48 Astro E2 48 binoculars 48 CCD camera 48 Planetary Laboratory 48 RS Ophiuchi 48 polarimetric 48 Mars Pathfinder lander 48 Hanny Voorwerp 48 Kuiper belt objects 48 Harlow Shapley 48 rover panoramic 48 Upsilon Andromedae b 48 planetary scientist 48 spy satellites 48 Space Telescope Science 48 GRB # 48 photometry 48 THEMIS spacecraft 48 SETI 48 constellation Cassiopeia 48 lensing galaxy 48 Comet Hartley 48 ALMA antennas 48 Doppler radars 48 solar flares 48 synthetic aperture radar 48 CubeSats 48 HARPS N 48 cosmic magnifying glass 48 ultraviolet imaging spectrograph 48 airborne observatory 48 Astrophysics 48 Planck telescope 48 Martian rovers 48 Stratospheric Observatory 48 polar orbiting satellites 48 elliptical galaxy NGC 48 LCROSS 48 Observatory NOAO 48 impactor spacecraft 48 constellation Centaurus 47 star IM Pegasi 47 Planck spacecraft 47 unaided eye 47 NASA ESA Hubble 47 Mars orbiting spacecraft 47 Haehnelt 47 STEREO 47 Large Telescope SALT 47 twin Voyager spacecraft 47 Lulin 47 Orion nebula 47 Comet Halley 47 KH #D 47 galaxies 47 Celestron 47 confocal microscope 47 infrared detector 47 waxing crescent 47 NIRCam 47 rover Opportunity 47 telescope eyepiece 47 NASA Jet Propulsion Laboratory 47 MetOp 47 Alpha Centauri 47 interferometric observations 47 ROCSAT 2 47 cosmological distances 47 refractors 47 TanDEM X 47 foreground galaxy 47 thermal emission spectrometer 47 Mars rovers 47 Orionids 47 William Herschel Telescope 47 Huygens probe 47 Antenna LISA 47 CAPE CANAVERAL Astronauts 47 galaxy NGC 47 Square Kilometre Array SKA 47 C1XS 47 exo planets 47 Hubble Space telescope 47 planets orbiting sun 47 MG J# +# 47 SkyScout 47 polar orbiting 47 Crab Pulsar 47 Hinode 47 brightest supernova 47 defile Mauna Kea 47 located atop Mauna 47 SpaceWeather.com 47 interferometry 47 Spectroscopic Explorer 47 Zeta Ophiuchi 47 JDEM 47 Mars landers 47 neutrino particles 47 Arches Cluster 47 High Resolution Imaging 47 Sidewalk Astronomers 47 skywatchers 47 TrES 4 47 SELENE 47 Rosetta lander 47 millisecond pulsars 47 NEOSSat 47 ASTRON 47 cosmic cannibal 47 Heterodyne Instrument 47 astrophysicists 47 Diviner instrument 47 orbiter lander 47 Small Magellanic Cloud 47 meteor shower 47 neutrino detectors 47 X ray binary 47 Gamma ray Large 47 lunar orbits 47 supernova remnant 47 Magnetic Imager HMI 47 SPIRE instrument 47 Cancri e 47 HRSC 47 telescopic 47 transiting planets 47 OGLE TR #b 47 N. Rathnasree 47 Orbiting Carbon Observatory 47 moon Io 47 Arecibo 47 Orbiter 47 WASP #b 47 galaxy cluster 47 amateur skywatchers 47 Moessbauer spectrometer 47 Cloud Aerosol Lidar 47 Gravity Probe 47 millisecond pulsar 47 AB Aurigae 47 geosynchronous satellites 47 Kepler 47 Infrared Pathfinder Satellite 47 asteroid Lutetia 47 Libra constellation Vogt 47 Infrared Mapping Spectrometer VIMS 47 airglow 47 JCMT 47 XMM Newton X ray 47 telescopes atop Mauna 47 GMRT 47 galaxy M# [002] 47 Moon Mineralogy Mapper M3 47 faraway planets 47 Voyager probes 47 Deep Impact spacecraft 47 robotic arm 47 star Proxima Centauri 47 supernova 47 asteroids orbiting 47 Virgo cluster 47 orbiters 47 planets Uranus 47 Planck 47 Starfire Optical Range 47 Philae lander 47 starlight 47 ecliptic plane 47 domed lookout 47 refurbished Hubble Space 47 asteroid Itokawa 47 Extragalactic 47 X ray spectrometer 47 Observatory LIGO 47 Ocean Salinity SMOS 47 infrared ultraviolet 47 Stargazing Live 47 Kuiper Belt Object 47 binocular 47 star Fomalhaut 47 parabolic mirror 47 CRISM 47 synchrotron 47 orbiter Mars Odyssey 47 optical interferometry 47 satellites orbiting 47 TerraSAR X 47 ESA Proba 47 Martian rover 47 pointings 47 NICMOS 47 Lunar Reconnaissance Orbiter 47 Nasa 47 Saturnian moon Titan 47 Synthetic Aperture Radar 47 Krimigis 47 twin STEREO spacecraft 47 nanosatellites 47 faraway galaxies 47 scanning electron microscope 47 adaptive optics AO 47 ESA Rosetta 47 NASA Kepler spacecraft 47 Astronomer 47 Moessbauer 47 Ultraviolet Imaging Spectrograph UVIS 47 NASA Cosmic Background 47 Cubesat 47 SECCHI 47 Galilean satellites 47 inflatable planetarium 46 aurora 46 occultation 46 microscopic imager 46 X ray Telescope 46 Phoenix Mars lander 46 Project Ozma 46 Mauna Kea 46 Comet Tempel 1 46 NASA 46 Boethin 46 Infrared Astronomical Satellite IRAS 46 robotic Canadarm 46 planetary astronomer 46 parabolic dish 46 Slooh 46 SeaWiFS 46 Red Rectangle 46 ESA Envisat 46 Kepler observatory 46 GIOVE B 46 microscopes 46 Jupiter Ganymede 46 Lunar Reconnaissance Orbiter Camera 46 constellation Cygnus 46 X ray detector 46 Climate Experiment GRACE 46 coronal loops 46 particle smasher 46 constellations Cygnus 46 Large Telescope Salt 46 irregularly shaped asteroid 46 luminous galaxies 46 UA Steward Observatory 46 Kepler Space Telescope 46 refractor 46 Fresnel lens 46 Smos 46 rare wekiu bug 46 asteroids 46 planets orbiting distant 46 Dynamics Observatory 46 Crab Nebula 46 millimeter wavelengths 46 visible wavelengths 46 Ellery Hale 46 hyperspectral 46 CARTOSAT 46 StarDate 46 Anik F2 46 red supergiant 46 planet HD #b 46 constellation Lyra 46 cosmic ray observatory 46 RY Sagittarii 46 Lulin Observatory 46 highly elliptical orbits 46 moon 46 filamentary structure 46 Composite Infrared Spectrometer 46 CHIPSat 46 parabolic antennas 46 inch reflector telescope 46 barred spiral galaxy 46 WIYN telescope 46 Stardust capsule 46 gravitational lensing 46 Orbiting Carbon Observatory OCO 46 constellation Ursa Major 46 inhabitable planets 46 discover Fomalhaut 46 particle accelerator 46 Dumbbell Nebula 46 CMB radiation 46 Tidbinbilla 46 Saturnian system 46 Apollo missions 46 Beta Pictoris b 46 Milky Way galaxy 46 Fomalhaut 46 eclipsing binary 46 Reflection Radiometer 46 Deep Impact probe 46 Resolution Imaging 46 Field Imager WFI 46 Space Agency 46 constellation 46 Comet 9P/Tempel 1 46 Applied Physics Laboratory 46 pulsars 46 Field Infrared Survey 46 pulsar 46 Proba 46 moons Phobos 46 multibeam 46 Bug Nebula 46 Arizona Steward Observatory 46 orbiter Cassini 46 periodic dimming 46 VLTI 46 extragalactic 46 GOCE 46 NASA Lunar Reconnaissance 46 interferometric 46 stellar occultation 46 robotic lander 46 attosecond 46 Ikonos 46 planetarium dome 46 ATLAS detector 46 radial velocity technique 46 NSLS II 46 robotic rover 46 Kepler #b 46 Infrared Camera 46 thermal infrared 46 Hubble gyroscopes 46 X ray emission 46 LADEE 46 PASADENA Calif. Astronomers 46 gamma ray observatories 46 Deep Impact flyby spacecraft 46 Huygens mission 46 HiRISE images 46 waxing gibbous moon 46 Hubble Space Telescopes 46 Pierre Auger Observatory 46 orbiter robotic arm 46 Cosmic Microwave Background 46 Cassini orbiter 46 Mercury flyby 46 Cepheid variables 46 Mars Surveyor 46 zodiacal light 46 GLAST Burst Monitor 46 UVIS instrument 46 SuperWASP 46 potentially habitable planets 46 Lagoon Nebula 46 Herschel SPIRE 46 NASA CloudSat 46 Science Experiment HiRISE 46 celestial fireworks 46 Ionosphere Sounding 46 astrophysicist 46 Lunar Orbiter 46 Proba 2 46 gamma ray spectrometer 46 astronomy buff 46 superconducting magnet 46 detect gamma rays 46 Chajnantor 46 constellation Taurus 46 Las Campanas Chile 46 fluorescence microscope 46 Mars orbiters 46 Planetary Science Institute 46 ENVISAT 46 Mars rovers Spirit 46 Lunokhod