1. Radio Telescopes

2. Angular resolution Distant objects are separated by an angle. –Degrees, arc-minutes, arc-seconds Angular resolution refers to the ability to see objects that are close together. primaryfocal pointeyepiece

3. Diffraction Light passing through an aperture is diffracted. The limit of resolution is set by the aperture. University of Birmingham (UK) in nm  in arcsec D in cm

4. Radio Waves Radio waves are light with wavelengths longer than a millimeter. –FM and TV at a few meters –AM radio at 300 m –Microwaves at a few cm The first parabolic radio telescope was built in 1937 in Wheaton, IL by Grote Reber.

5. Wavelength and Resolution Angular resolution is proportional to diameter divided by wavelength. Large wavelengths need larger “mirrors”. Radio waves need large dishes to get good resolution. The Arecibo telescope:Arecibo telescope In Puerto Rico; 305 m (1000 ft) dish; covers 18 acres.

6. Radio Dish Focal point can be above (Prime) or in the dish (Cassegrain). An antenna is used instead of a camera. Haystack Observatory

7. Radio Emissions Objects in space behave differently in radio frequencies. Visible light shows the thermal properties of stars. Radio shows the behavior of gases between stars. Milky Way with visible light.Milky Way with 74 cm radio.

8. Telescope Arrays Two (or more) telescopes can look at the same object. –Increases the aperture and improves resolution The combined signals use interferometry.

9. Very Large Array The VLA is a group of 27 telescopes in New Mexico. –25 m diameter dish –Moveable telescopes up to 36 km separation –Resolution of 0.04 arcseconds at = 0.7 cm. This is equivalent to seeing a golf ball 100 miles away. Very Large Array

10. VLBI Very long baseline interferometry combines signals from across the earth.