3D representation of the NonRotating Origin

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3D representation of the Non-Rotating Origin

• Olivier de Viron and Veronique Dehant
• Royal Observatory of Belgium
• Scientific adviser
• Nicole Capitaine

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The Terrestrial Reference Frame
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The Celestial Reference Frame
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2 systems in an ideal world
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The less ideal world
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Only the intermediate system is different when
using the new or the old formalism. The
definition of the TRF and CRF are not affected.
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The old-version transformation
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1. From TRF to CIP
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2. To the True equinox of the date
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How to go from one equinox another?
Ecliptic 1
Equator 1
g1
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How to go from one equinox another?
Z
Ecliptic 1
Ecliptic 2
gi
Equator 1
g1
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How to go from one equinox another?
Ecliptic 2
gi
Equator 1
x
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How to go from one equinox to another?
Z
Ecliptic 2
g2
gi
Equator 1
Equator 2
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How to go from one equinox to another?
Ecliptic 2
g2
x
Equator 2
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How to go from one equinox another?
Ecliptic 2
g2
x
Equator 2
It took 5 successive steps
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True ecliptic of the date
Mean ecliptic of the date
Equator at J2000
True equator of the date
Mean equator of the date
gv
g0
Ecliptic at J2000
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The new transformation
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1. From TRF to CIP
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2. From the terrestrial NRO
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3. Earth Rotation Angle
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4. To the XCRF projection s
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5. To CRF celestial motion of the CIP
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What is the NRO
1. Characterized by its motion no velocity
around the CIP equator associated with polar
motion or nutation.
2. Not a point in particular, any point of the
CIP equator can work.
3. Allows to get rid of the equinox in the change
of reference frame.
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So, we can take any points we want?
1. Yes, it is not the point it-self that matter,
but its motion.
2. But, we want the new system to be consistent
with the old one.
3. Thus, the point is chosen to insure continuity.
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Conclusions
The NRO is defined by
its position at the base epoch (continuity)
its motion (no motion in the CIP equator
associated with polar motion).
Only the Intermediate system is involved, no
change of the CRF or TRF