1. Types of Telescopes

Why build telescopes to gather light at different wavelengths?

e.g., The Milky Way, M81, M51 Orion

sensitivity and image quality: depth

Do different types of telescopes have to be built to gather light at different wavelengths?      

Constraints:

A new generation of ground-based telescopes:

WIYN (early 1990's technology): interior, exterior

HET (late 1990's technology): exterior, mirror segments, top view

SALT . . . UW's Mk-II of this new design.    [Robert Stobie Spectrograph]

2. Instruments

Imagers -- cameras, to take pictures

Spectrographs -- to take spectra

both use:

Detectors -- most often today, a CCD

CCD = Charge Coupled Device      

pixels

3. Diffraction limit      

diffraction: (arcsecond) = 2.5x10⁵ /D

= wavelength (units: meters)

D = telescope diameter (units: meters)

4. Techniques for Improving Image Quality

Adaptive optics -      

Correct for atmospheric blur, ``seeing'' by deforming the mirror to compensate for atmospheric distortions

Interferometry -      

Use an array of telescopes to synthesize a larger aperture.

This reduces the diffraction limit.

(a) building a bigger telescope

(b) observing below the atmosphere

(c) observing at shorter wavelengths

(d) use a CCD with bigger pixels

(e) using adaptive optics

(a) refractive optics

(b) reflective optics

(c) monolithic mirrors

(d) segmented mirrors

(e) adaptive optics