1. Science 9: Unit E: Space Exploration Topic 5: What Channel is That?

2. Electromagnetic Radiation ► Light is one kind of electromagnetic radiation (EMR). Stars and other celestial objects give off all kinds of EMR: the Sun sends out infrared radiation which warms the Earth, UV radiation which tans/burns our skin, and radio waves which we detect as static on our radios.

3. History of Radio Astronomy ► Radio astronomy is the studying of radio waves given off by these celestial objects in order to learn more about them. ► In the 1930s telephone engineers noticed that there was a constant source of background radio radiation which interfered with their equipment. Karl Jansky built a radio antenna to study these signals and concluded that the signals came from outer space. ► Grote Reber, using a radio dish, discovered that certain areas in the sky gave off especially strong radio signals. Reber noted that the strongest radio signal came from the Sun, followed by Jupiter. He also noticed that outside the solar system, the strongest signal came from the center of the Milky Way Galaxy, full of stars. Objects that gave off especially strong signals were called Radio Objects.

4. Radio Astronomy Cont’d ► Using radio waves to study celestial objects has one major disadvantage: They don’t produce as much detail as light. Our eyes cannot see radio waves so we lose information. A major advantage is that radio waves can travel farther because they’re larger and pass through dust clouds while light waves cannot. ► Computers now produce images showing the strength of radio signals: weak signals are bluish while stronger signals get redder and finally white.

5. Interferometry and the VLA ► Interferometry – The use of many telescopes combined together so that the many radio signals could be combined by computer to produce a much more detailed single signal. The biggest example of radio interferometry is the Very Large Array (VLA) in New Mexico. This array has been used to study radio signals from alien sources. So far no luck.

6. Very Long Baseline Interferometry (VLBI) ► Very Long Baseline Interferometry (VLBI) – A much larger and newer example of interferometry that relies on radio telescopes connected wirelessly over a much larger distance, even the entire planet.