Telescopes

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Slide 117

What is resolution?

The resolution of an interferometer is equal to:

wavelength

baseline

Another way to increase the resolution is to

build an interferometer.

Slide 118

Radio interferometer

baseline

VLA

Slide 119

Film clip of the Very Large Array (VLA)

from

“Contact”

Slide 120

Interference

Slide 121

Sea interferometer

The "Sea Interferometer", was formed by combining Yagi arrays with the surface of the sea near Syndey, Australia.

The antenna could observe both direct radiation from the sun and those reflected from the surface of the sea. The direct and reflected waves interfered with each other producing the characteristic fringe pattern of an interferometer with a baseline roughly twice that of the cliff.

1947 First radio interferometric observations by McCready (Sydney, Australia)

Slide 122

Resolution of an interferometer

Field of view =

Wavelength / dish diameter

Resolution = Wavelength / baseline

Slide 123

Resolution of an interferometer

30arc sec

10 arc sec

30arc sec

5 arc sec

Greatly magnified views

Longer baseline

Slide 124

Resolution of an interferometer

BIMA observations of the emission from HCN and C4H in IRC+10216. The synthesized beamsizes are shown in the lower right of each panel.

Slide 125

Aperture synthesis

Another name for interferometry is aperture synthesis.

One is trying to synthesize the aperture of a large single dish with several smaller dishes.

Slide 126

Aperture synthesis

Advantage

Increased resolution

Disadvantage

Less sensitivity

Slide 127

Aperture synthesis

baseline

VLA

Slide 128

Some examples of interferometers

Slide 129

Radio interferometer