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byCatherine HohenkerkHM Nautical Almanac

UK Hydrographic Office

Implementation of the New Nomenclaturein

The Astronomical Almanac

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Facts @ The Astronomical Almanac

•Joint Publication of USNO & HMNAO•Reference product for the year•Not a text book •Must maintain standards; up to date; reliable •Not at the leading edge•Useful to users; & Users require continuity

Production [deadlines; funding; personnel]

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Some Chronology•2000 Aug: IAU 2000 Resolutions•2002 Dec: IERS Software•2003 Jan: IAU 2000 Resolutions to be used• Apr: SOFA release • July: IAU Sydney• Nov: IAU WG NFA•2004 Jan: AsA 2005 •2005 Jan: AsA 2006, IAU 2000, CIO & CIP•2006 Jan: AsA 2007•2006 July: preparing AsA 2008 for Jan 2007

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Implementation in the AsA of:

•IAU 2000 Resolutions� ICRS & Frame Bias� IAU 2000 precession-nutation� “New paradigm”

•the procedures using the origin determinedby the position of the pole and “s” rather than the traditional ecliptic and equator.

•Earth rotation angle

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The AsA & The AsA OnlineUSNO – sectionsC – SunE – PlanetsF– SatellitesH – StarsL – GlossaryM – Notes & References

HMNAO – sectionsA – PhenomenaB – Times scales &

reference systemsD – MoonG – Minor planetsK – Reference data

•IAU 2000 precession-nutation usedin all sections,

•Some interaction between sections

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� New tables � New explanation

� Adding new material into existing pages

� Update software

Things to Consider for Section B

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Existing Quantities:Universal & Sidereal Times (GMST/GAST/GAST–GMST)Nutation and obliquity (∆ψ, ∆ε, ε)Precession and nutation matrix (NPB)Position & velocity of Earth

New Quantities:Universal Time & Earth rotation angle (ERA) ERA – GAST (equation of the origins)Celestial intermediate pole & origin: X, Y, sMatrix from ICRS to intermediate positions (C)

B: Quantities to be Tabulated

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Relationship between GAST & ERA

Schematic Diagram

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Planetary Reduction

CIO-baseda) Apply C(X,Y,s) to give

Celestial Intermediate Reference System

b) Apply ERA

3. Calculate hour angle (GHA) and declination (δδδδ).

OR

Equinox-baseda) Apply NPB to give

the true equinox and equator of date

b) Apply GAST.

1. GCRS: calculate geocentric vector, apply corrections for light-time, light deflection, aberration as appropriate;

2. Rotations: transform GCRS to required “of date” system;

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Extract from Planetary Reduction

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Some Terms / Acronyms

ICRS — International Celestial Reference System

BCRS Barycentric Celestial Reference System

GCRS — Geocentric Celestial Reference System

Equator & Equinox of Date CIO and Equator of DateCIRS — Celestial Intermediate

Reference System

Difference: Equation of the origins = ERA – GAST

ERA, Earth rotation angleGAST ( or GST)

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Some Terms / Acronyms

TIRS—Terrestrial Intermediate Reference SystemTIO and equator of date

ITRS—International Terrestrial Reference System

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CIO BasedCelestial Intermediate Ref. Sys.CIP (X, Y)Celestial Intermediate EquatorCIO – CIO locator sIntermediate placeIntermediate RADeclinationERAHour angle

Equinox BasedTrue Equator & Equinox of dateCIP (X, Y)True equator of dateTrue equinox of dateApparent placeApparent RADeclinationGASTHour angle

Summary of Nomenclature in AsA

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•IAU WG Nomenclature for Fundamental Astronomy

•SOFA•NOVAS & USNO Circular 179

•The Astronomical Almanac •2007 is available•2008 to be published Jan 2007

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Finally some Resources