Talk:Celestial coordinate system

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Contents 1 U V W Space velocities 2 Zodiac Coordinate System 3 Prime Meridian 4 Plural title?

[edit] U V W Space velocities

Wikipedia appears to have no definition of the U V W system for describing space velocities. I'm not sure of the canonical name of the system, or an official definition, but it appears that in the right-handed system,

 *  U is the component toward the galactic center
 *  V is the component along the galactic rotation
 *  W is the component toward the galactic north pole

Does anyone have more confidence on the canonical name and a reference for a definition? --NealMcB 03:36, 9 April 2007 (UTC)

I am not familiar with any galactocentric coordinate system for stars. However, it seems like this systems would be very difficult to use. For velocities, the main problem would be measuring velocities that are perpendicular to the line of sight, which is difficult to do for most stars. This may be worth writing an article, but it should not be used in articles on individual stars.

However, I can say that a general cylindrical coordinate system like the one above is used in creating models of disk galaxies. I can give references if needed. Dr. Submillimeter 09:58, 9 April 2007 (UTC)

JThorstensen here -- can't seem to log on from home. I think you're nearly correct, except the U component appears to be directed away from the Galactic Center, making the system left-handed. It actually is possible to get perpendicular velocities for stars provided you can measure a proper motion and an accurate distance, which is generally do-able for relatively nearby stars, e.g. those within parallax range -- you need to nail the proper motion down really accurately when solving for the parallax, anyway. There's a newly (as of 2007) revised article on the galactic coordinate system (l and b) which gives the exact IAU definition. Incidentally, as a fellow professional astronomer and wikipedia newbie I've found the quality of astronomy articles to be highly variable -- some are really excellent, some are very inaccurate. Caveat emptor!

[edit] Zodiac Coordinate System

This is a nice comparison article. May I suggest adding the Zodiac Coordinate system — used by Ptolemy and other ancient astronomers — to the table. It uses the ecliptic as it fundamental plane, the ecliptic poles as its poles but in contrast with the ecliptic coordinate system it uses stars (Antares and Aldebaran) as its fixed frame of reference and therefore requires no epoch. Actually, I believe there are two separate zodiac coordinate systems. One sidereal system using the fixed stars and requiring no epoch and one tropical zodiac using an epoch fixed to the vernal equinox around the time and Hipparchus. It's a useful coordinate system for those with very few modern day instruments. 41.248.252.130 (talk) 21:20, 11 May 2008 (UTC)

[edit] Prime Meridian

The suggestion of a zodiac celestial coordinate system also raises the issue of the prime meridian for the coordinate system. It might be worth having another column in the table for that too. 41.248.252.130 (talk) 22:40, 11 May 2008 (UTC)

[edit] Plural title?

It seems to me that the title should be plural, "Celestial coordinate systems", since the article refers to several. --George100 (talk) 12:00, 7 June 2008 (UTC)