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AstronomicalInstrumentsDR. FABIEN BARON
21) Telescopes: characteristics & designs2) Ground vs space observations3) Optical instruments (visible, infrared, ultraviolet)4) Non-optical instruments (radio, X-ray, gamma)Outline
3Three basic components of a modern system formeasuring radiation from astronomical sources:a telescope: a “bucket” for collecting visiblelight (or radiation at other wavelengths).an instrument: sorts the incoming radiation bywavelength.a detector: a device that senses the radiation inthe wavelength regions we have chosen andpermanently records the observations.Credit: NASAThe Hubble Space Telescope carries multiple instruments,optimizedfordifferentwavelengthsandtasks.Eachinstrument has its own detector.Telescopes are giant eyes that collect radiation
41.Sensitivity: how faint can the telescope detectobjects?This is determined by the light-collecting area of the telescope, itself determinedby the telescope diameter. Telescopes with alarger collecting area can gather a greater amountof light in a shorter time.GSU’sHard Labor Creek Observatory0.6 mGemini North Telescope8 mYour eye7 mmImportant properties of a telescope:Sensitivity
5Credits: ESOSimulated observations for different telescope sizes (equivalent diameters added by F. Baron)2.4 m8 m100 m50 cmAngular resolution: what are thesmallest details the telescope can see?Angular resolution is the capability of anyimage-forming device such as an opticalor radio telescope to distinguish smalldetails of an object.A better angular resolution providessharper images, while a lower one willhave blurrier details. Angular resolutionget better with larger telescope diameterand smaller wavelength of observation.A large telescope observing objects invisible light will yield better resolutionthan a small telescope observing ininfrared light.Note: human eyes have an angular resolution of one arcminute (30cm at 1km distance, 8” at 1 mile)Important properties of a telescope:Angular resolution
6Refracting Telescopes focus light with lenses:Light enters a refracting telescope through a lens atthe upper end, which focuses the light near thebottomofthetelescope. An eyepiece thenmagnifies the image so that it can be viewed by theeye, or a detector like a photographic plate can beplaced at the focus.Reflecting Telescopes focus light with mirrors:The upper end of a reflecting telescope is open,and the light passes through to the mirror located atthe bottom of the telescope. A second mirrortypically reflect the light to a position outside thetelescope structure, where an observer can haveeasier access to it.Refracting vs reflecting telescopes
Refracting vs reflecting telescopes7Two surfaces to polish per lens.

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Term
Fall
Professor
ClarkKris

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