Spectrum

Much of the information we have from the universe comes from light. Sunlight, actually starlight, is made up of many different colors. We can see this by holding a prism up to the sunlight. The prism separates the light into the individual colors of the rainbow — the visible light spectrum.

Yet the light we can see represents only a very small portion of the electromagnetic spectrum. On one end of the spectrum are radio waves having wavelengths billions of times longer than those of visible light. On the other end are gamma rays, with wavelengths millions of times shorter than those of visible light. Wavelength is directly related to the amount of energy the waves carry. The shorter the radiation's wavelength, the higher its energy. Although the amount of energy carried by each wavelength differs, all forms of radiation travel at the speed of light — 186,000 miles (300,000 km) per second.

• Radio waves are used to transmit radio and television signals. Radio wavelengths range from less than a centimeter to hundreds of meters.
  
  
• Infrared radiation (700 nm to 1 mm) is longer in wavelength than visible light. Infrared radiation is invisible to the human eye.
  
  
• The rainbow of colors that we know as visible light has wavelengths between 400 and 700 billionths of a meter (400 to 700 nanometers).
  
  
• Ultraviolet wavelengths are shorter than visible light, ranging from 400 nm down to 10 nm. Sunlight contains ultraviolet radiation — which can burn our skin — but most of it is blocked by ozone in Earth's upper atmosphere.
  
  
• X-rays — high-energy waves with great penetrating power — range from about 10 billionths of a meter to 10 trillionths of a meter.
  
  
• Gamma rays, with wavelengths of less than 10 trillionths of a meter, are even more penetrating than X-rays.