NARRATION: Microwaves can pop your popcorn. They can catch you speeding. They carry thousands of phone channels to speed your calls. But, can microwaves help us learn about our world and our universe? Let’s find out.
With wavelengths ranging from 30 centimeters down to 1 millimeter, microwaves fall between radio waves and infrared. Microwaves are used in Doppler radar, which is widely used for short term localized weather forecasting and what you see on TV weather news. Satellites have revolutionized weather forecasting by providing a global view of weather patterns and surface temperatures. This unique perspective has greatly increased the accuracy of tropical storm and climate forecasts.
Different wavelengths of microwaves, grouped into bands, provide different information to scientists. Medium length C band microwaves penetrate through clouds, dust, smoke, snow, and rain to reveal the Earth’s surface. Satellite microwave measurements reveal the full Arctic sea ice cover every day, even where clouds exist. These measurements show great variability from year to year, but, also an overall decrease in Arctic sea ice since the late 1970s, illustrated here with maps and a time series of Arctic sea ice in September, at the end of the summer melt.
The Japanese Earth Resources satellite uses longer wavelength L band microwaves for forest mapping by measuring surface soil moisture, such as this image of the Amazon basin, to identify areas of recent deforestation. L band microwaves are also used by global positioning systems, such as the one in your car.
Scientists routinely combine microwave information with information from other parts of the EM spectrum to study the composition of cosmic dust or of a supernova, such as this supernova image that combines X-ray, radio, and microwave data. This recently known supernova in the Milky Way exploded just over 140 years ago at the time of the American Civil War.
One important phenomenon is unique to microwaves. In 1965, using long L band microwaves, Arno Penzias and Robert Wilson made an incredible accidental discovery. They detected what they thought was noise from their instrument, but was actually a constant background signal coming from everywhere in space. This radiation is called cosmic microwave background, and if our eyes could see microwaves, the entire sky would glow with a nearly uniform brightness in every direction. The existence of this background radiation has served as important evidence supporting the Big Bang Theory for how our universe began.
Microwaves have become both staples and wonders of modern life. They are also the backbone of communications and of Earth sensing systems, and they are an excellent guide to the ancient history and origins of our universe.