Incorrect symbol of the astronomical unit

Unidata / UDUNITS-2

API and utility for arithmetic manipulation of units of physical quantities

http://www.unidata.ucar.edu/software/udunits

Other

62 stars 36 forks source link

Incorrect symbol of the astronomical unit #36

Closed pascaloettli closed 9 years ago

pascaloettli commented 9 years ago

Currently, udunits2 (version 2.2) uses "ua" as symbol for the astronomical unit, and 1 ua is equal to 149,598,000,000 m

$ udunits2 -H ua -W m
    1 ua = 1.49598e+11 m
    x/m = 1.49598e+11*(x/ua)

$ udunits2 -H au -W m
udunits2: Units are not convertible

However, according to this resolution of the XXVIIIe General Assembly of International Astronomy Union (2012), the symbol should now be "au" and 1 au should be equal to 149,597,870,700 m exactly.

semmerson commented 9 years ago

The definition for "astronomical unit" that UDUNITS-2 uses came from the US National Institute of Standards and Technology (NIST). See http://physics.nist.gov/Pubs/SP811/appenB9.html#LENGTH. It's possible they got both the abbreviation and value wrong.

I'll investigate.

semmerson commented 9 years ago

I modified the value of the unit "astronomical_unit" and added the symbol "au". I also added the new unit "astronomical_unit_BIPM_2006" (with symbol "ua") for the old value.

These changes will be in the next release, which might take a while as I'm swamped and the UDUNITS continuous-delivery pipeline is currently broken.