Exa-

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This article is about the SI prefix. For the X Window System acceleration architecture, see EXA. For The CAE software developer, see Exa Corp..

Look up exa- in Wiktionary, the free dictionary.

Exa- (symbol E) is a prefix in the metric system denoting 10¹⁸ or 1000000000000000000.

Adopted in 1975, it comes from the Greek ἕξ, used as a prefix ἑξά-, meaning six (like hexa-), because it is equal to 1000⁶.

Examples:

1 EeV = 10¹⁸ electronvolts = 0.1602 joule
1 exasecond is approximately 32 billion years
1 exametre is approximately 110 light years
0.43 Es ≈ the approximate age of the Universe
1.6 Em — 172 ± 12.5 light years — Diameter of Omega Centauri (one of the largest known globular clusters, perhaps containing over a million stars)^[1]^[2]

SI prefixes
Prefix	Symbol	1000^m	10ⁿ	Decimal	Short scale	Long scale	Since^{[n 1]}
yotta	Y	1000⁸	10²⁴	1000000000000000000000000	Septillion	Quadrillion	1991
zetta	Z	1000⁷	10²¹	1000000000000000000000	Sextillion	Trilliard	1991
exa	E	1000⁶	10¹⁸	1000000000000000000	Quintillion	Trillion	1975
peta	P	1000⁵	10¹⁵	1000000000000000	Quadrillion	Billiard	1975
tera	T	1000⁴	10¹²	1000000000000	Trillion	Billion	1960
giga	G	1000³	10⁹	1000000000	Billion	Milliard	1960
mega	M	1000²	10⁶	1000000	Million		1960
kilo	k	1000¹	10³	1000	Thousand		1795
hecto	h	1000^2/3	10²	100	Hundred		1795
deca	da	1000^1/3	10¹	10	Ten		1795
		1000⁰	10⁰	1	One		–
deci	d	1000^−1/3	10⁻¹	0.1	Tenth		1795
centi	c	1000^−2/3	10⁻²	0.01	Hundredth		1795
milli	m	1000⁻¹	10⁻³	0.001	Thousandth		1795
micro	μ	1000⁻²	10⁻⁶	0.000001	Millionth		1960
nano	n	1000⁻³	10⁻⁹	0.000000001	Billionth	Milliardth	1960
pico	p	1000⁻⁴	10⁻¹²	0.000000000001	Trillionth	Billionth	1960
femto	f	1000⁻⁵	10⁻¹⁵	0.000000000000001	Quadrillionth	Billiardth	1964
atto	a	1000⁻⁶	10⁻¹⁸	0.000000000000000001	Quintillionth	Trillionth	1964
zepto	z	1000⁻⁷	10⁻²¹	0.000000000000000000001	Sextillionth	Trilliardth	1991
yocto	y	1000⁻⁸	10⁻²⁴	0.000000000000000000000001	Septillionth	Quadrillionth	1991
^ The metric system was introduced in 1795 with six prefixes. The other dates relate to recognition by a resolution of the CGPM.

[edit] See also

^ distance × sin( diameter_angle ), using distance of 5 kpc (15.8 ± 1.1 kly) and angle 36.3', = 172 ± 12.5 ly.
^ van de Ven, G.; van den Bosch, R. C. E.; Verolme, E. K.; de Zeeuw, P. T. (January II 2006). "The dynamical distance and intrinsic structure of the globular cluster ω Centauri". Astronomy and Astrophysics 445 (2): 513–543. Bibcode 2006A&A...445..513V. doi:10.1051/0004-6361:20053061. "best-fit dynamical distance D=4.8±0.3 kpc ... consistent with the canonical value 5.0±0.2 kpc obtained by photometric methods"