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What is an eV?

An eV (short for electron Volt) is a unit astronomers often use to measure energy. It corresponds to the energy needed to move an electron through one Volt of potential. An electron Volt is well-liked by astronomers because it is about the right amount of energy to affect individual particles such as those found in space. For example, 13.6 eV of energy will strip one electron off a Hydrogen atom. Such "singly ionized Hydrogen" is very common throughout the Universe.

To give a better idea of how much energy an eV really is, it is useful to know that air molecules at room temperature have an energy of about 0.024 eV and air molecules at a million degrees have about 100 eV of energy. Particles in a gas that emits in the X-rays (keV range) have temperatures of hundreds of millions or even billions of degrees Celsius.


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Imagine the Universe! is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

The Imagine Team
Project Leader: Dr. Barbara Mattson
Curator: J.D. Myers
Responsible NASA Official: Phil Newman
All material on this site has been created and updated between 1997-2014.
This page last updated: Monday, 27-Sep-2004 11:26:09 EDT