Exa-

This article is about the SI prefix. For other uses, see Exa (disambiguation).

Exa is a unit prefix in the metric system denoting 10¹⁸ or 1000000000000000000. It was added to the International System of Units (SI) in 1975,^[1] and has the unit symbol E.

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

Examples:

The total storage needed by Google Mail as of April 2012, ignoring backups and compression, is more than an exabyte (10240 megabytes of storage per user multiplied by an estimated 260 million users).
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)^[2]^[3]

Prefix		1000^m	10ⁿ	Decimal	English word		Since^{[n 1]}
name	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	thousand trillion	1991
exa	E	1000⁶	10¹⁸	1000000000000000000	quintillion	trillion	1975
peta	P	1000⁵	10¹⁵	1000000000000000	quadrillion	thousand billion	1975
tera	T	1000⁴	10¹²	1000000000000	trillion	billion	1960
giga	G	1000³	10⁹	1000000000	billion	thousand million	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	thousand millionth	1960
pico	p	1000⁻⁴	10⁻¹²	0.000000000001	trillionth	billionth	1960
femto	f	1000⁻⁵	10⁻¹⁵	0.000000000000001	quadrillionth	thousand billionth	1964
atto	a	1000⁻⁶	10⁻¹⁸	0.000000000000000001	quintillionth	trillionth	1964
zepto	z	1000⁻⁷	10⁻²¹	0.000000000000000000001	sextillionth	thousand trillionth	1991
yocto	y	1000⁻⁸	10⁻²⁴	0.000000000000000000000001	septillionth	quadrillionth	1991

↑ The metric system was introduced in 1795 with six metric prefixes. The other dates relate to recognition by a resolution of the General Conference on Weights and Measures (CGPM).

References

↑ "Resolution 10 of the 15th meeting of the CGPM (1975)". International Bureau of Weights and Measures. Retrieved 2012-04-18.
↑ 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. arXiv:astro-ph/0509228. 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 Check date values in: |date= (help)

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