facts @ the astronomical almanac - obspm.fr · 1 by catherine hohenkerk hm nautical almanac uk...
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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