Midterm Distribution31 A’s, 37 B’s, 26 C’s, 21 D’s, 17 F’s

Common Mistakes

Do the algebra first! Units, Units, Units Does your answer make sense? Using ratios

Lecture 18:

Telescopes and

Observational Astronomy

There are two kinds of telescopes

RefractingRefracting: a lens is used to focus the light from distant objects.

ReflectingReflecting: a primary mirror is used to gather and focus light.

A Refracting Telescope

A Reflecting Telescope

Alternative designs for reflecting telescopes

Charge Coupled Devices (CCD)

Fundamental Telescope Properties

Light collecting area (diameter of primary mirror or lens)

angular resolution (smallest angular distance that can be resolved clearly) limited by effects of Earth’s atmosphere

Angular Separation

= 360o . s /(2d) “small angle formula”

Angular Resolution

Diffraction

The Diffraction Limitdiffraction limit = 2.5 x 105 x wavelength of light(arcsec) diameter of telescope

Find the diffraction limit of the 2.4 m Hubble Space Telescope for visible light (500 nm).

d.l. = 2.5 x 105 (500 x 10-9 m/2.4 m) = 0.05 arcsec

Where to put your telescope high and dry – to minimize the blurring

effects of the Earth’s atmosphere and emission/absorption from water vapor

away from light pollution with roads, electricity, and other support

systems nearby

The Summit of Mauna Kea

The Keck Telescopes

The Magellan Telescopes

Basic Functions of Telescopes

Imaging/photometryaccurate measurement of light intensity filters can be used to separate into different

colors spectroscopy

light spread out using a diffraction grating time sequence

how an object’s brightness changes with time

A Basic Spectrograph

Spectral Resolution

Telescopes across the spectrum

Hubble Space Telescope

Infra-red Telescopes

SOFIA

SIRTF

Radio Telescopes

Arecibo

Very Large Array (VLA)

Interferometry An array of smaller

telescopes can be used together

the light gathering power is equal to the sum of all the areas

the angular resolution is greatly improved

X-ray Telescopes

grazing incidence mirror

Chandra X-ray Observatory

Compton Gamma-ray Observatory

Images of non-visible light

Radio

CO

FIR

NIR

vis.

X-ray

gammaray