Parallax and Radial Velocity

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/node208.html | 92 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 92 insertions(+) create mode 100644 src/slalib/sun67.htx/node208.html (limited to 'src/slalib/sun67.htx/node208.html') diff --git a/src/slalib/sun67.htx/node208.html b/src/slalib/sun67.htx/node208.html new file mode 100644 index 0000000..cc2b337 --- /dev/null +++ b/src/slalib/sun67.htx/node208.html @@ -0,0 +1,92 @@ + + + + +Parallax and Radial Velocity + + + + + + + + + + + + +

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+
+ Next: Aberration +
+Up: EXPLANATION AND EXAMPLES +
+ Previous: Proper Motion +

+Parallax and Radial Velocity +

+For the utmost accuracy and the nearest stars, allowance can +be made for annual parallax and for the effects of perspective +on the proper motion. +

+Parallax is appreciable only for nearby stars; even +the nearest, Proxima Centauri, is displaced from its average +position by less than +an arcsecond as the Earth revolves in its orbit. +

+For stars with a known parallax, knowledge of the radial velocity +allows the proper motion to be expressed as an actual space +motion in 3 dimensions. The proper motion is, +in fact, a snapshot of the transverse component of the +space motion, and in the case of nearby stars will +change with time due to perspective. +

+SLALIB does not provide facilities for handling parallax +and radial-velocity on their own, but their contribution is +allowed for in such routines as +sla_PM, +sla_MAP +and +sla_FK425. +Catalogue mean +places do not include the effects of parallax and are therefore +barycentric; when pointing telescopes etc. it is +usually most efficient to apply the slowly-changing +parallax correction to the mean place of the target early on +and to work with the geocentric mean place. This latter +approach is implied in Figure 1. +

+ +

+
+ Next: Aberration +
+Up: EXPLANATION AND EXAMPLES +
+ Previous: Proper Motion +

+SLALIB --- Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
12 October 1999
E-mail:ptw@star.rl.ac.uk +

+ + -- cgit