Astronomical ObservationsAstronomical observationsWhat telescopes are for? Why do they need to be big?Telescope InstrumentsPowerPoint PresentationReminder: the electromagnetic spectrumSlide 7Visible LightElectromagnetic Radiation in every day life (sort of)Slide 10Blackbody RadiationThere are telescopes for every portion of the electromagnetic spectrumDifferent locations for telescopesMost wavelengths cannot penetrate the Earth's atmosphereWhy different wavelengths are requiredOptical/near-infrared telescopes, ground-based observatoriesSlide 17Slide 18Slide 19Slide 20Slide 21Why putting optical telescopes in space? Eliminating the atmospheric blurringSlide 23Slide 24Slide 25The Five College Radio Astronomy ObservatoryUMass LMTOptical Sky: starlight, dustRadio Sky: gas and mag. fieldSoft X-ray Sky: neutron stars and black holesSpectra contain physical information of stars and galaxies Shape of the spectrum, its peak and the absorption lines tell us the temperature and the chemistry of this starSpectral Lines of Some ElementsThe X-ray to Radio spectrum of the Sun understanding the Sun global propertiesAstronomical ObservationsAstronomical ObservationsSo, really, what is that astronomers do at the telescope?Astronomical observationsAstronomical observations•Most observations are made by recording, in various ways, electromagnetic radiation emitted by astronomical sources. •Pretty much most observations are one of two types:•Imaging•Images obtained with the purpose of studying the morphology of the source and measuring the intensity of its light•Spectroscopy•Special observations that disperse the wavelength of the incoming light and record the intensity of eachWhat telescopes are for?What telescopes are for?Why do they need to be big?Why do they need to be big?The main purpose of a telescope is The main purpose of a telescope is to collect as much light as possibleto collect as much light as possible•Like an antenna: the stronger the signal the clearer the transmission.Like an antenna: the stronger the signal the clearer the transmission.•Well, guess what: an antenna *is* a telescope (a radio one, that is)Well, guess what: an antenna *is* a telescope (a radio one, that is)The larger the light collector, I.e. the primary mirror or lens, the more The larger the light collector, I.e. the primary mirror or lens, the more powerful the telescope (Light Gather Power= LGP).powerful the telescope (Light Gather Power= LGP).In other words, the In other words, the Light Gathering Power Light Gathering Power (LGP) of a telescope is (LGP) of a telescope is proportional to the area of its light-capturing element (primary mirror or proportional to the area of its light-capturing element (primary mirror or lens)lens)•LGP ~ 4 LGP ~ 4  D D22•LGPLGPAA/LGP/LGPBB = (D = (DAA/D/DBB))22•A telescope twice as large collects four times as much lightA telescope twice as large collects four times as much lighte.g. a 8-meter telescope and a 8-meter telescope: the former collects (8/4)e.g. a 8-meter telescope and a 8-meter telescope: the former collects (8/4)22=4 more light in a given =4 more light in a given time than the latter.time than the latter.The other primary feature is image The other primary feature is image sharpnesssharpness, to faithfully reproduce , to faithfully reproduce detailsdetails•Resolving power: Resolving power:  = 11.6/D = 11.6/DThe last, and least important, feature is The last, and least important, feature is magnificationmagnificationTelescope InstrumentsTelescope InstrumentsCamera: the instrument for imagingCamera: the instrument for imaging•To obtain images at desired wavelength or To obtain images at desired wavelength or wavelengths (for color images)wavelengths (for color images)•This yields the morphology, size of the sources, and This yields the morphology, size of the sources, and which part of the source has which color.which part of the source has which color.Spectrometer: the instrument for spectroscopySpectrometer: the instrument for spectroscopy•To study the intensity of the various wavelengths To study the intensity of the various wavelengths (colors)(colors)•This yields the physical nature (star, galaxy, black This yields the physical nature (star, galaxy, black hole), chemical composition, physical properties hole), chemical composition, physical properties (temperature, density), dynamics (motions, mass), (temperature, density), dynamics (motions, mass), distance of the sources distance of the sourcesImaging(incl. spatial distribution, color of the light)Spectra(chemistry of the objectand its velocity)Both with imaging and spectroscopythere are three basic aspects ofthe light from an object that we can study from the Earth.Variability(change with time)Reminder:Reminder:the electromagnetic spectrumthe electromagnetic spectrumVisible light isn’t the whole story. It’s just a small Visible light isn’t the whole story. It’s just a small part of the entire electromagnetic spectrumpart of the entire electromagnetic spectrumLong Wavelength(high frequency)(high energy)Short Wavelength(low frequency)(low energy)Visible LightVisible LightShorterWavelengthLongerWavelengthElectromagnetic RadiationElectromagnetic Radiationin every day life (sort of)in every day life (sort of)Short wavelengthLong wavelengthBlack body radiation:the peak wavelength (i.e. the color) tells us the temperature of the emitting sourceBlackbody RadiationBlackbody RadiationThere are telescopes for every portion There are telescopes for every portion of the electromagnetic spectrumof the electromagnetic spectrumDifferent wavelengths carry different type of information (Different wavelengths carry different type of information (optical: optical: stars; X-ray: black hole; infrared: dust; radio: gasstars; X-ray: black hole; infrared: dust; radio: gas))To detect different wavelengths of light, eg. X-ray, UV, optical, To detect different wavelengths of light, eg. X-ray, UV, optical, infrared, radio, different technologies are requiredinfrared, radio, different technologies are required For example, special mirrors are necessary for X-ray telescopes or For example, special mirrors are necessary for X-ray telescopes or else the radiation would pass through them.else the radiation would pass through them.Not only that: our atmosphere transmits (i.e. lets go through) only Not only that: our atmosphere transmits (i.e. lets go