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    December 18, author updated article according to reviewers suggestions. All changes from reviewer W.van Altena are accepted. Most of the suggestions from the review shown below are now implemented, except for the summary section, which rather is a short introduction into the topic itself with a mix of some history and outlook of the main text. The other reviewer and the author prefer to keep this as is.


    This is a very nice article. I only have a few comments. My apologies for the delay in reviewing.

    1. Summary. "Astrometry is the science...".

    This intro seems a bit jumbled. I think you have to decide if this is a historical introduction, or whether it's a summary of the article. Recommend you focus on the points in the last sentence ("Measurements of distances to celestial objects by triangulation..."), rather than the confusion in terminology.

    I think it would be much cleaner to make the Intro a pure summary, and have a separate section on 'History'. You could place it either before or after the section on 'Angles'. The History section would be a good place to explain how the terminology got to be confusing.

    2. missleading -> misleading

    3. 'Angles'. "Astrometry is about angles..." True, but better to say "Astrometry is about measuring angles, and the derivation of astrophysical quantities from those measurements.

    4. Celestial coordinates. reference is made to Hipparcos. It needs its own link. And add to the list of 'External links' at the end.

    5. 'Stars do move'. "This is the domain of narrow-field, small-angle, differential astrometry....". I think you need to add some explanation here. Otherwise, the contrast with wide-angle astrometry is not made clear. perhaps split this topic into 2 subsections? At a minimum, clearly define 'differential'.

    6. Eichhorn's book. Need to indicate there is a full reference at the end.

    7. "The astrometric method is the only way to determine the masses...". This isn't quite true. For a transiting system, RV can measure the companion mass, as the inclination is known.

    8. The Space Interferometry Mission (SIM). Goes by the name SIM Lite these days (SIM not spelled out, usually) to distinguish it from an earlier study.

    9. General comment:

    There are numerous references to topics outside of the article - telescopes, instruments, and various terminology items. It appears that, unlike, say, Wikipedia, the links are supposed to be internal (to Scholarpedia). But without a lot of supporting articles, the many references are tantalizing rather than helpful. A way to address this would be to make a few more entries under 'External Links'.

    User 3 (User:): The determination of radial velocities has moved down the astronomical pyramid.

    Resolution No. C2 on the Definition of "Astrometric Radial Velocity"

    Divisions I, IV, V, VI, VII, IX and X, and Commissions 8, 27, 29, 30, 31, 33, 34 and 40 of the International Astronomical Union

    Recognizing: That recently improved astrometric techniques may permit the accurate determination of stellar radial velocities independent of spectroscopy, thus requiring a definition independent from spectroscopic measures;

    Considering: That the change in the barycentric direction u to objects outside of the solar system is customarily expressed by the proper-motion vector µ = du/dtB, where tB is the barycentric coordinate time (TCB) of light arrival at the solar system barycenter;

    Therefore recommend: That the geometric concept of radial velocity be defined as vr = dr/dtB, where r is the barycentric coordinate distance to the object and tB the barycentric coordinate time (TCB) for light arrival at the solar system barycenter.

    XXIVth General Assembly in Manchester (August 2000)

    Norbeck 22:55, 26 January 2011 (CST)

    Author : Norbert Zacharias: User 3 thanks for the info!

    I updated the "astrometry" article with respect to "radial velocity" and added a link to the IAU GA resolutions.

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