ESA title
Science & Exploration

W - X - Y - Z

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ESA / Science & Exploration / Space Science


Watt (W)

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


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.



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


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.



Zonal wind

Atmospheric wind component which flows along the latitude.

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