USNO Circular 179 - U.S. Naval Observatory

Abbreviations and Symbols
Frequently Used
and index to most relevant sections
α right ascension 3.2
δ declination 3.2
∆ψ nutation in [ecliptic] longitude (usually expressed in arcseconds) 5.3, 5.4.2
∆ɛ nutation in obliquity (usually expressed in arcseconds) 5.3, 5.4.2
ɛ mean obliquity of date 5.4.1
ɛ ′ true obliquity of date (= ɛ + ∆ɛ) 5.4.2
ɛ0 mean obliquity of J2000.0 5.3, 5.4.1
θ Earth Rotation Angle 2.3, 6.2
µas microarcecond (= 10 −6 arcsecond ≈ 4.8×10 −12 radian)
σ a non-rotating origin or, specifically, the CIO 6.2
σ unit vector toward a non-rotating origin or, specifically, the CIO 6.5.1
Υ the equinox 3.2, 6.2
Υ unit vector toward the equinox 6.5.1
as or ′′ arcsecond (= 1/3600 degree ≈ 4.8×10 −6 radian)
AU astronomical unit(s)
B frame bias matrix 3.5
BCRS Barycentric 1 Celestial Reference System 1.2
BIPM Bureau International des Poids et Mesures
C matrix for transformation from GCRS to Eσ 5.4.3, 6.5.3
cen century, specifically, the Julian century of 36525 days of 86400 seconds
CIO Celestial Intermediate Origin 2 3 6.2, 6.5.1
CIP Celestial Intermediate Pole 5.2, 6.5.1
CIRS (See Eσ)
E Υ instantaneous (true) equator and equinox of date 6.4, 6.5.3
Eσ Celestial Intermediate Reference System (CIRS) 6.4, 6.5.3
Eϖ Terrestrial Intermediate Reference System (TIRS) 6.4, 6.5.3
EΥ equation of the equinoxes 2.3, 2.6.2
Eo equation of the origins 6.5.1.1, 6.5.4
ESA European Space Agency
FKn n th Fundamental Catalog (Astronomisches Rechen-Institut, Heidelberg) 3.3
GAST Greenwich apparent sidereal time 2.3, 2.6.2
GCRS Geocentric Celestial Reference System 1.2
x