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