In this series of blogs I have been exploring the different types of waves in the electromagnetic spectrum. I have written about radio, infrared, ultraviolet, gamma waves and x-rays. This blog finishes this topic with microwaves.
The Cosmic Microwave Background (CMB) is radiation from around 400,000 years after the start of the Universe and thought to be remnants from the big bang. Microwaves were first predicted by James Clerk Maxwell in 1864 by mathematical equations. In 1888 Heinrich Hertz proved the existence of microwaves by building a device that produced and detected microwave radiation.
The prefix “Micro” is usually used to infer that the waves are in the micrometer range. However in this case the prefix simply means that the waves are shorter than radio waves. They travel by line of sight which means they cannot bend over the horizon, bend round obstacles or reflect off the ionosphere. This effectively restricts terrestrial microwave communication to a range of 40 miles. Since the waves are absorbed by gasses in the atmosphere causing degradation of the signal, the practical distance is 1 kilometre.
Microwaves have frequencies ranging from about 1 billion cycles per second, or 1 gigahertz (GHz), up to about 300 gigahertz and wavelengths of about 30 centimeters (12 inches) to 1 millimeter (0.04 inches). As with other waves microwaves can be subdivided into L, S, C, X and K. Due to the short wavelength, antennas need only be 1 to centimetres in length making them idea for mobile and wireless phones, wifi, bluetooth and laptops.
The first Cosmic Microwave Background (CMB) tests to be conducted in space, were carried out by NASA’s Cosmic Background Explorer (COBE) satellite. In 1992, COBE confirmed that the temperature of the CMB varied according to the part of the sky being monitored. Measurements suggested that over angular scales larger than 10 degrees, the CMB temperature varies by about one part in 100 000 from the average value of 2.73 Kelvin.
In 2003 the Wilkinson Microwave Anisotropy Probe (WMAP) dramatically improved the map’s clarity and sharpness. This helped to determine the age, and the amount of the different types of matter and energy contained in the universe. It also ruled out some potential theories related to its beginning and evolution.
Between 2009 and 2013 Planck further increased resolution allowing it to distinguish details in the structure of the CMB that have been invisible so far, and bring it into sharp focus. The implication is that the conditions of the Universe close to the Big Bang can be probed more accurately than ever before.
By now you should have a basic knowledge of the electromagnetic spectrum and how it is related to radio astronomy. For my next topic I have been set the challenge of researching thermal and non thermal mechanisms. Watch this space.