HubbleSite - Spectrum 101

Wavelengths in nanometers
(One meter equals 1,000,000,000 nanometers. One nanometer is about the length of ten atoms in a row.)

The Electromagnetic Spectrum

Spectrum 101

ll the information we have from the universe comes from light. White light such as starlight is made up of the individual colors of the rainbow — the visible light spectrum.

Each color of the spectrum represents a different wavelength. For example, an object that we see as red reflects the "red" wavelength of light and absorbs all the other colors of the spectrum.



There are different ways to isolate different types of light. For example, although our eyes cannot see ultraviolet light from a star, one way to gain a record of it is to let the star's light pass through a filter and then fall on a special detector.

Hubble uses special filters to "screen out" the types of light from an object that astronomers are not currently studying. These filters allow only a certain range of light wavelengths through. Once the unwanted light has been filtered out, the resulting light is allowed to fall onto one or more light-sensitive detectors.

This produces a "picture" of the star in the selected wavelength. Since the detectors can detect light outside the visible light spectrum, the use of filters allows scientists to see "invisible" objects — those only visible in ultraviolet and infrared wavelengths.

The filter wheel is rotated so the desired filter intercepts the light beam.
Wavelength is the distance between two successive wave crests or troughs.


Visible light is a form of electromagnetic radiation — along with radio waves, microwaves, infrared radiation, ultraviolet rays, X-rays, and gamma rays. All electromagnetic radiation travels through space at the speed of light, or 186,000 miles (300,000 km) per second.

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 of the spectrum are gamma rays, with wavelengths millions of times smaller 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.