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CH3 - Astronomy 1F03 2010/11 Fall Term 2010/11 Chaisson&...

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Unformatted text preview: Astronomy 1F03 2010/11 Fall Term 2010/11 Chaisson & McMillan, Astronomy Chapter 3 Telescopes Telescopes Telescopes Telescopes are the tools Astronomers use to capture light from space from What are What Telescopes for? Primarily Telescopes are light buckets buckets Many sources of light in space are extremely faint and can’t be are be seen with something as small as an eye as All telescopes collect light in proportion to their area proportion Optical Telescopes: Optical Visible Light Optical telescopes can be built from lenses or mirrors mirrors Lenses: Refractor Lenses: Mirrors: Reflector Mirrors: The goal is to get all the light falling on a larger area and to focus it down to a small area for viewing or other measurements area Lenses: Refractor Telescopes Lenses: Light entering glass at an angle is bent at This can be used to build a telescope build Lenses: Refractor Telescopes Lenses: Binoculars are a pair of refracting telescopes telescopes Galileo used a refractor for the first astronomical observations observations Refractor Problems: Refractor Glass bends different colors different amounts (chromatic aberration) aberration) Glass absorbs light – particularly particularly non-visible light non Big lenses are heavy Big lenses are expensive to make Big Mirrors: Reflecting Telescopes Mirrors: Mirrors can also be used to focus light focus Mirrors can be thin – unlike unlike lenses Mirrors don’t absorb light Mirrors absorb Mirror reflect all wavelengths at the same angle angle All big modern telescopes use mirrors Forming an image Forming An image is formed at the focal point An Different Types of Reflectors of Prime Focus, Newtonian (designed by Isaac Newton), Cassegraine, Cassegraine Coude Coude The difference is about where the instruments or observers sit observers e.g. A Spectrograph to e.g. measure the spectrum measure Hubble Hubble at prime focus focus Telescope Qualities: Telescope Sensitivity Keck Keck 10m Larger telescopes collect more light – iin n proportion to the area of the mirror proportion Faint details become visible Telescope Qualities: Telescope Diffraction Limits The sharpness of the image is limited by physics: the wave nature of light by Light waves are diffracted which makes the image fuzzy the Due to diffraction: Due Resolution is better for larger Resolution mirrors and shorter wavelength light wavelength Diffraction Limit to resolution Diffraction θ = 0.25 λLIGHT DMIRROR Angular resolution, θ (arcseconds ”) λ wavelength of light (µm), D mirror diameter (m) Hubble ~ 0.25 x 0.500 µm/2.5 m ~ 0.05” Keck (10m) ~ 0.01” Keck Resolution Problems: Resolution The atmosphere Air behaves a bit like glass – iit bends light t too but it isn’t too consistent consistent Turbulence and other variations in the atmosphere limit the resolution from earth to ~ 0.4-1” earth Being high up helps: Being Build on mountains The view from Space: The The Hubble Space Telescope (HST) Above the atmosphere the Hubble Space Telescope can achieve the theoretical limit to its resolution limit This is about 20 times better than a standard earth-based telescope earth Earth HST The Hubble The Revolution HST is has a small mirror (2.4m), but revolutionary: Amazing angular resolution ~ 0.05 arcsec arcsec Can point it for a long time It is probably the most productive telescope ever productive Next time it breaks, it wont be serviced serviced Next big space telescope JWST JWST JWST (formerly NGST) JWST James Webb Space Telescope 6.5 m mirror, optimized for IR 6.5 Will be actively cooled (liquid Helium), therefore limited life therefore Will sit at L2 (Lagrange Point), orbiting the Sun, not Earth - unrepairable Launch 2014? Launch Adaptive Optics Adaptive You can correct for the distortion by the atmosphere if you tilt and distort the telescope mirror(s) fast enough! telescope Space is still better but we have bigger telescopes we on the ground Keck has achieved ~ 0.04” Photography & Telescopes Telescopes Digital Cameras use Charge Coupled Devices (CCDs) to capture images Devices This technology was developed for astronomy Photographic emulsions were used before before Now it’s all digital Now Radio Radio Astronomy The atmosphere is transparent to visible light and radio waves and Radio waves are very weak – you need big you telescopes to get anywhere anywhere BUT you get new information! information! Radio waves: The cold universe, Magnetic Fields Magnetic Visible light is associated with hot gas Visible Radio waves let us see very cold gas as you expect from the Black Body idea you Magnetic fields make electrons oscillate like in an antenna – with radio you can with see where there are magnetic fields in space space Arrays of Telescopes: Telescopes: Interferometry Radio telescopes have poor resolution because diffraction is a big problem at long wavelengths long An array of telescopes can be used like one very large telescope to combat this problem problem Space Telescopes Space UV, Infrared, X-rays and Gamma rays UV, rays all have to be observed from space all In addition the telescopes are harder to build, particularly for short wavelengths build, Space telescopes are expensive and may have limited life spans may Infrared: Need a cold telescope Infrared JWST will be cooled for infrared JWST X-ray: Hard to focus: X-rays don’t reflect only graze reflect Chandra Compton Gamma Rays: Can’t focus at all, Gamma focus hard to pin down where they came from came New wavelenths: wavelenths New insight Looking at our Milky Looking Way Galaxy we see different things at each wavelength wavelength Radio Infrared Visible X-rays Gamma-Rays New wavelengths: New New insight dust Young stars Hot Stars Orion Molecular Cloud: Visible vs. IR The Milky Way The at 5 wavelengths • Radio: Cold gas without stars • Infrared: Warm gas and dust Infrared: making new stars and planets making • Visible: Stars, planets • X-rays: Gas falling into Black rays: Holes, Supernovae, super hot gas gas • Gamma-Rays: Super Rays: explosions or exotic objects at the edge of physics the Radio Infrared Visible X-rays Gamma-Rays ...
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