Experimental Astrophysics AAS Editor in Chief Ethan Vishniac, Johns Hopkins University, Maryland, USA About the program: AAS-IOP Astronomy ebooks is the official book program of the American Astronomical Society (AAS), and aims to sharein depththe mostfascinating areas of astronomy, astrophysics, solar physics and planetary science. The program includes publications in the following topics: Books in the program range in level from short introductory texts on fast-moving areas,graduateandupper-levelundergraduatetextbooks,researchmonographsand practical handbooks. For a complete list of published and forthcoming titles, please visit iopscience.org/ books/aas. About the American Astronomical Society The American Astronomical Society (aas.org), established 1899, is the major organization of professional astronomers in North America. The membership (∼7,000) also includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising the contemporary astronomical sciences. The mission of the Society is to enhance and share humanity’s scientific understanding of the universe. Editorial Advisory Board Steve Kawaler Joan Najita Iowa State University, USA National Optical Astronomy Observatory, USA Ethan Vishniac Johns Hopkins University, USA Daniel Savin Columbia University, USA Dieter Hartmann Clemson University, USA Stacy Palen Weber State University, USA Piet Martens Georgia State University, USA Jason Barnes University of Idaho, USA Dawn Gelino NASA Exoplanet Science Institute, James Cordes Caltech, USA Cornell University, USA Experimental Astrophysics Elia Stefano Battistelli University of Roma la Sapienza, Physics Department, Rome, Italy IOP Publishing, Bristol, UK ªIOPPublishingLtd2021 Allrightsreserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem ortransmittedinanyformorbyanymeans,electronic,mechanical,photocopying,recording orotherwise,withoutthepriorpermissionofthepublisher,orasexpresslypermittedbylawor undertermsagreedwiththeappropriaterightsorganization.Multiplecopyingispermittedin accordancewiththetermsoflicencesissuedbytheCopyrightLicensingAgency,theCopyright ClearanceCentreandotherreproductionrightsorganizations. CertainimagesinthispublicationhavebeenobtainedbytheauthorsfromtheWikipedia/ Wikimediawebsite,wheretheyweremadeavailableunderaCreativeCommonslicenceorstated tobeinthepublicdomain. Pleaseseeindividualfigurecaptionsinthispublicationfordetails. To theextentthatthelawallows,IOPPublishingdisclaimanyliabilitythatanypersonmaysufferasa resultofaccessing,usingorforwardingtheimage(s). Anyreuserightsshouldbecheckedand permissionshouldbesoughtifnecessaryfromWikipedia/Wikimediaand/orthecopyrightowner (asappropriate)beforeusingorforwardingtheimage(s). PermissiontomakeuseofIOPPublishingcontentotherthanassetoutabovemaybesought [email protected]. EliaStefanoBattistellihasassertedhisrighttobeidentifiedastheauthorofthisworkin accordancewithsections77and78oftheCopyright,DesignsandPatentsAct1988. ISBN 978-0-7503-3119-7(ebook) ISBN 978-0-7503-3117-3(print) ISBN 978-0-7503-3120-3(myPrint) ISBN 978-0-7503-3118-0(mobi) DOI 10.1088/2514-3433/ac0ce4 Version:20211001 AAS–IOPAstronomy ISSN2514-3433(online) ISSN2515-141X(print) BritishLibraryCataloguing-in-PublicationData:Acataloguerecordforthisbookisavailable fromtheBritishLibrary. PublishedbyIOPPublishing,whollyownedbyTheInstituteofPhysics,London IOPPublishing,TempleCircus,TempleWay,Bristol,BS16HG,UK USOffice:IOPPublishing,Inc.,190NorthIndependenceMallWest,Suite601,Philadelphia, PA19106,USA ...to Patrizio, Penelope, Miriam, and Magda “E′ cosí bello fissare il cielo e accorgersi di come non sia altro che un vero e proprio immenso laboratorio di fisica che si srotola sulle nostre teste.” “Itissonicetostareattheskyandrealizehowitisnothingmorethanarealimmense physics laboratory that unrolls on our heads.” Margherita Hack Contents Preface xiv Author Biography xvi Contributors xvii 1 Astrophysical Observables 1-1 1.1 Astrophysical Information Carriers 1-1 1.2 Cosmic Rays 1-2 1.3 Meteorites 1-5 1.4 Cosmic Dust 1-7 1.5 Gravitational Waves 1-8 1.6 Neutrinos 1-10 1.7 Dark Matter 1-12 2 Astronomical Optics 2-1 2.1 Electromagnetic Waves 2-1 2.2 Observables 2-4 2.2.1 Flux, Brightness, and Magnitude 2-4 2.2.2 Spectral Densities 2-6 2.2.3 Photometric Bands 2-7 2.2.4 Throughput, Etendue, and AΩ 2-12 2.3 Geometrical Optics: Snell’s Law 2-14 2.4 Lenses and Mirrors 2-18 2.4.1 Lenses 2-18 2.4.2 Mirrors 2-20 2.4.3 Lens AΩ 2-21 2.5 Diffraction and Interference 2-23 3 Telescopes 3-1 3.1 Diffraction-limited Telescopes or Not? 3-1 3.2 Refractive Telescopes 3-4 3.3 Reflective Telescopes 3-7 3.4 Telescope Mounts 3-12 3.5 Telescopes Construction 3-15 3.5.1 Telescopes Around the World 3-15 ix