Science glossary

W - X - Y - Z


W

Watt (W)

Unit of power in the SI unit system. 1 Watt = 1 Joule per second.

Wavelength

The distance between two peaks of a wave. See also Electromagnetic radiation and Frequency.

White dwarf

A very dense star with a mass below 1.4 solar masses that is no longer burning nuclear fuel. The Sun will one day evolve into a white dwarf with a diameter of 10 000 km.
 
 
 X

X-band

A band of radio frequencies extending from 5200 to 10 900 MHz

X-ray

Electromagnetic radiation with wavelengths between those of ultraviolet and gamma rays, approximately 0.01-10 nm. At these short wavelengths, it is more common to talk in terms of photon energies. These energies range from 0.1-100 keV.

X-ray (hard)

Higher-energy part of the X-ray spectrum ranging from approximately 5 keV to 100 keV.

X-ray (soft)

Band of low energy X-rays, between 0.1 keV and approximately 5 keV.
 
 
  
Last update: 9 May 2012


Index

 •  A (http://www.esa.int/esaSC/SEMVH0S1VED_index_0.html)
 •  B (http://www.esa.int/esaSC/SEMLJ0S1VED_index_0.html)
 •  C (http://www.esa.int/esaSC/SEMMU1S1VED_index_0.html)
 •  D (http://www.esa.int/esaSC/SEM2X1S1VED_index_0.html)
 •  E (http://www.esa.int/esaSC/SEMCX1S1VED_index_0.html)
 •  F (http://www.esa.int/esaSC/SEMOX1S1VED_index_0.html)
 •  G (http://www.esa.int/esaSC/SEM1Y1S1VED_index_0.html)
 •  H (http://www.esa.int/esaSC/SEM112S1VED_index_0.html)
 •  I (http://www.esa.int/esaSC/SEMK12S1VED_index_0.html)
 •  J - K - L (http://www.esa.int/esaSC/SEMU12S1VED_index_0.html)
 •  M (http://www.esa.int/esaSC/SEM822S1VED_index_0.html)
 •  N - O (http://www.esa.int/esaSC/SEMT32S1VED_index_0.html)
 •  P (http://www.esa.int/esaSC/SEMYB2S1VED_index_0.html)
 •  Q - R (http://www.esa.int/esaSC/SEMZH2S1VED_index_0.html)
 •  S (http://www.esa.int/esaSC/SEMDL2S1VED_index_0.html)
 •  T - U - V (http://www.esa.int/esaSC/SEM763S1VED_index_0.html)