modern telescopes lecture 12. imaging astronomy in 19c photography in 19c revolutionize the...

Modern Telescopes

Lecture 12

Imaging Astronomy in 19c

Photography in 19c revolutionize the astronomyability to collect light (photons) over long time =

long exposurescan see fainter object.film “catch” only 1 photons out of 50 incoming.

Efficiency is about 2%

Charge-Coupled-Device (CCD) = digital camera about 70% efficiency images can be displayed on computer

screen in real time. “remote observation” : observing Keck telescopes in Hawaii from 1000s km away.

In the old days, astronomers are using photographic plates (film on glass).

Photometry measurements of brightness of objects

1.6m by 3 m sizecovers 3.5° field of view3600 Mega pixels

Large Synoptic Survey Telescope (8m) Camera

image the entire viewable sky every 2-3 nights

Produce about 15TB data evey night

Measuring spectraone of the most important usage of telescopes

Spectrograph = a device that records spectra = diffraction grating + CCD

Spectroscopy

diffraction pattern from CDs

Two types of Spectra

Absorption Spectrum Emission Spectrum

Atmospheric Transmission

Because of the Earth Atmosphere, observations at Gamma-ray, X-ray, UV, far-infrared, long radio wavelengths should be done in space!

Go beyond the atmosphere SOFIA (Stratospheric Observatory For

Infrared Astronomy)

2.5m telescope in a flying Boeing 747!

Will fly at 41,000 feet (12km!).

Radio telescopesUsing parabolic metal dish

(reflecting antenna).

Molecules in space… (organic molecules!!)

Angular resolution in interferometry mode = two+ telescopes observing the same astronomical object resulting an angular resolution of a single telescope (whose diameter is equal to the baseline of two telescopes).

Parkes telescopeAustralia, 64m

Radio Astronomy

Because of the diffraction limit of telescope (θ = λ / D), although radio telescopes are large (30-60 m), images taken at radio wavelengths are lower resolution.

Map of Saturn taken with VLA at 2cm.

Radio telescopes in interferometry mode Very Large Array (VLA) : 27 antennae over ~20km arm. New Mexico

Very Large Baseline Interfemetry Radio telescopes over several continents Compared to a single-dish radio telescope, VLBI

can produce 10,000+ better resolution images.

VLBI in space Ground-based radio telescopes + radio telescope in Earth orbit

Infrared Telescopes

Orion in Optical Orion in Infrared

Ultraviolet & Infrared Telescopes

Spitzer IR telescope (85cm) Hubble telescope (2.4m)

Non-optical wavelengths carry additional information!

Next Generation Space Telescope James Webb Space Telescope (JWST) 6.5m telescope Earth-trailing orbit

X-ray TelescopesExplore objects with temperatures

of > 106 degrees

For example, Super-massive black-hole at M87 (nearby galaxy)

European X-ray Telescope

False-color images SuperNova remnant (Supernova exploded 325 years ago) Three space telescopes (X-ray : blue, Hubble: green, Spitzer: red)

In summary…

Important ConceptsAtmospheric WindowsMulti-wavelength astronomy

Important TermsPhotometrySpectroscopyCCD

Chapter/sections covered in this lecture : sections 6-4 through 6-7