Science 9: Unit E: Science 9: Unit E: Space ExplorationSpace Exploration

Topic 5: What Channel is Topic 5: What Channel is That?That?

Electromagnetic RadiationElectromagnetic Radiation► Light is one kind of electromagnetic radiation Light is one kind of electromagnetic radiation

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

History of Radio AstronomyHistory of Radio Astronomy► Radio astronomy is the studying of radio waves Radio astronomy is the studying of radio waves

given off by these celestial objects in order to learn given off by these celestial objects in order to learn more about them.more about them.

► In the 1930s telephone engineers noticed that In the 1930s telephone engineers noticed that there was a constant source of background radio there was a constant source of background radio radiation which interfered with their equipment. radiation which interfered with their equipment. Karl Jansky built a radio antenna to study these Karl Jansky built a radio antenna to study these signals and concluded that the signals came from signals and concluded that the signals came from outer space.outer space.

► Grote Reber, using a radio dish, discovered that Grote Reber, using a radio dish, discovered that certain areas in the sky gave off especially strong certain areas in the sky gave off especially strong radio signals. Reber noted that the strongest radio radio signals. Reber noted that the strongest radio signal came from the Sun, followed by Jupiter. He signal came from the Sun, followed by Jupiter. He also noticed that outside the solar system, the also noticed that outside the solar system, the strongest signal came from the center of the Milky strongest signal came from the center of the Milky Way Galaxy, full of stars. Objects that gave off Way Galaxy, full of stars. Objects that gave off especially strong signals were called Radio Objects.especially strong signals were called Radio Objects.

Radio Astronomy Cont’dRadio Astronomy Cont’d

► Using radio waves to study celestial objects has Using radio waves to study celestial objects has one major disadvantage: They don’t produce as one major disadvantage: They don’t produce as much detail as light. Our eyes cannot see radio much detail as light. Our eyes cannot see radio waves so we lose information. A major waves so we lose information. A major advantage is that radio waves can travel farther advantage is that radio waves can travel farther because they’re larger and pass through dust because they’re larger and pass through dust clouds while light waves cannot.clouds while light waves cannot.

► Computers now produce images showing the Computers now produce images showing the strength of radio signals: weak signals are bluish strength of radio signals: weak signals are bluish while stronger signals get redder and finally while stronger signals get redder and finally white.white.

Interferometry and the VLAInterferometry and the VLA

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

Very Long Baseline Very Long Baseline Interferometry (VLBI)Interferometry (VLBI)

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