Exa is a decimal unit prefix in the metric system denoting 1018 or 1000000000000000000. It was added as an SI prefix to the International System of Units (SI) in 1975,[1] and has the unit symbol E.
Exa comes from the ancient Greek héx, used as a prefix - hexá-, meaning six (like hexa-), because it is equal to 10006.
Examples:
Prefix | Base 10 | Decimal | English word | Adoption[nb 1] | |||
---|---|---|---|---|---|---|---|
Name | Symbol | Short scale | Long scale | ||||
yotta | Y | 1024 | 1000000000000000000000000 | septillion | quadrillion | 1991 | |
zetta | Z | 1021 | 1000000000000000000000 | sextillion | trilliard | 1991 | |
exa | E | 1018 | 1000000000000000000 | quintillion | trillion | 1975 | |
peta | P | 1015 | 1000000000000000 | quadrillion | billiard | 1975 | |
tera | T | 1012 | 1000000000000 | trillion | billion | 1960 | |
giga | G | 109 | 1000000000 | billion | milliard | 1960 | |
mega | M | 106 | 1000000 | million | 1873 | ||
kilo | k | 103 | 1000 | thousand | 1795 | ||
hecto | h | 102 | 100 | hundred | 1795 | ||
deca | da | 101 | 10 | ten | 1795 | ||
100 | 1 | one | - | ||||
deci | d | 10-1 | 0.1 | tenth | 1795 | ||
centi | c | 10-2 | 0.01 | hundredth | 1795 | ||
milli | m | 10-3 | 0.001 | thousandth | 1795 | ||
micro | ? | 10-6 | 0.000001 | millionth | 1873 | ||
nano | n | 10-9 | 0.000000001 | billionth | milliardth | 1960 | |
pico | p | 10-12 | 0.000000000001 | trillionth | billionth | 1960 | |
femto | f | 10-15 | 0.000000000000001 | quadrillionth | billiardth | 1964 | |
atto | a | 10-18 | 0.000000000000000001 | quintillionth | trillionth | 1964 | |
zepto | z | 10-21 | 0.000000000000000000001 | sextillionth | trilliardth | 1991 | |
yocto | y | 10-24 | 0.000000000000000000000001 | septillionth | quadrillionth | 1991 | |
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best-fit dynamical distance D=4.8±0.3 kpc ... consistent with the canonical value 5.0±0.2 kpc obtained by photometric methodsCheck date values in:
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