From d54fe7c1f704a63824c5bfa0ece65245572e9b27 Mon Sep 17 00:00:00 2001 From: Joseph Hunkeler Date: Wed, 4 Mar 2015 21:21:30 -0500 Subject: Initial commit --- src/slalib/sun67.htx/footnode.html | 224 +++++++++++++++++++++++++++++++++++++ 1 file changed, 224 insertions(+) create mode 100644 src/slalib/sun67.htx/footnode.html (limited to 'src/slalib/sun67.htx/footnode.html') diff --git a/src/slalib/sun67.htx/footnode.html b/src/slalib/sun67.htx/footnode.html new file mode 100644 index 0000000..b6bcb72 --- /dev/null +++ b/src/slalib/sun67.htx/footnode.html @@ -0,0 +1,224 @@ + + + + +Footnotes + + + + + + + + + + +

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...SLALIB +
The name isn't an acronym; +it just stands for ``Subprogram Library A''. +
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...papers; +
One frame not included in +Figure 1 is that of the Hipparcos catalogue. This is currently the +best available implementation in the optical of the International +Celestial Reference System (ICRS), which is based on extragalactic +radio sources observed by VLBI. The distinction between FK5 J2000 +and Hipparcos coordinates only becomes important when accuracies of +50 mas or better are required. More details are given in +Section 4.14. +
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...equinox. +
With +the introduction of the International Celestial Reference System (ICRS), the +connection between (i) star coordinates and (ii) the Earth's orientation +and orbit has been broken. However, the orientation of the +International Celestial Reference Frame (ICRF) axes was, for convenience, +chosen to match J2000 FK5, and for most practical purposes ICRF coordinates +(for example entries in the Hipparcos catalogue) can be regarded as +synonymous with J2000 FK5. See Section 4.14 for further details. +
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An equinox is, however, not required for coordinates +in the International Celestial Reference System. Such coordinates must +be labelled simply ``ICRS'', or the specific catalogue can be mentioned, +such as ``Hipparcos''; constructions such as ``Hipparcos, J2000'' are +redundant and misleading. +
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...catalogues. +
This was +true until the inception of the International Celestial Reference +System, which is based on the idea of axes locked into the +distant background. The coordinates +of the extragalactic sources which realize these +axes have no individual significance; there is a ``no net rotation'' +condition which has to be satisfied each time any revisions take +place. +
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+SLALIB -- Positional Astronomy Library +
+Starlink User Note 67 +
+P. T. Wallace +
+12 October 1999 +
+E-mail:ptw@star.rl.ac.uk +
+ + -- cgit