Astrophysics (Index) About

### dex

(order-of-magnitude, decimal exponent)
(a number or ratio's log base 10)

The term dex (for decimal exponent) refers to the exponent of a number in scientific notation, and has come to be used like a unit that specifies a number's order-of-magnitude. For example, 100 could be described as 2 dex, or two numbers that differ by a factor of 1000 could be said to differ by 3 dex. As such a unit, a dex is sometimes cited as a fraction (making it the value's more-precise log base 10) whereas a cited order-of-magnitude is commonly rounded to an integer. Within physics and astrophysics, the term dex is sometimes used, but order-of-magnitude is probably used more. A common circumstance is describing the ratio of two numbers by the ratio's dex or order-of-magnitude. Example of the dex in scientific notation:

```2.40×107
```

This number's dex as specified is 7 and the number could be described as "7 dex" or "having an order-of-magnitude of 7". It could also be described as "7.38 dex", which is the number's log base 10 not rounded to an integer. Example of a ratio as a dex: "Jupiter's and Earth's masses differ by 2.5 dex" (i.e., log10 of 318, their ratio).

(mathematics,terminology,unit)
Further reading:
http://en.wiktionary.org/wiki/dex
https://joe-antognini.github.io/astronomy/what-is-a-dex
http://www.physics.unlv.edu/~jeffery/astro/logarithm/logarithm.html
https://astronomy.stackexchange.com/questions/17911/understanding-dex

Referenced by pages:
axion (A0)
back-of-the-envelope calculation
barrier
CMB Stage-4 (CMB-S4)
cosmic dust
dark energy
dense core mass function (DCMF)
event horizon (EH)
exascale computing
free-fall time
fuzzy dark matter (FDM)
H-R diagram (HRD)
hyperfine structure
inflation
ionizing radiation
jansky (Jy)
Kelvin-Helmholtz timescale (KH timescale)
main-sequence lifetime (MS lifetime)
N-body problem
numerical analysis
planet formation
parts per million (PPM)
projected separation
SI
superluminous supernova (SLSN)
speed of light (c)
stellar dynamics
task-based parallelism (TBP)
time standard
valley of beta stability

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