From: mpound@astro.umd.edu (Marc Pound)
Newsgroups: alt.astrology
Subject: Re: 1992 QB1, Beyond Pluto
Date: 30 Sep 92 15:27:22 GMT
Organization: U. of Maryland @ College Park, Astronomy

In article <BvCsDr.E47@csn.org> lmpm@teal.csn.org (L. M. P. McPherson) writes:
>
>Douglas Kyle Pierce informs me that astronomers, like western astrologers,
>use the tropical zodiac, but they express positions in terms of time along
>the ecliptic. 


Incorrect. Astronomers commonly express position in one of two ways.

1) Celestial coordinates: Can be thought of as the projection of the 
   Earth's equator, poles, longitude and latitude lines on the sky 
   (commonly referred to as "the celestial sphere."  Right ascension is 
   the arc distance measure eastward along the celestial equator 
   (NOT the ecliptic!) to the hour circle of the object from a 
   reference point on the celestial equator. It is measured in hours 
   (0 to 24) and the reference point is the vernal equinox. 
   Declination is the arc distance of the object along an hour 
   circle north or south of the celestial equator. It is measure
   in degrees (-90 to +90) with 0 degrees being on the celestial
   equator.

   The vernal equinox is the one of the points on the celestial
   sphere where the celestial equator and the ecliptic intersect.
   Because of the Earth's precession, the vernal equinox and the
   celestial equator slowly move with respect to the stars, thus 
   the R.A. and Dec. of a star continually change. Astronomers 
   therefore must also specify the "epoch" of the coordinates 
   given, e.g. 2000.0.  Epoch 2000.0 means "with respect to where the 
   vernal equinox will be in the year January 1, 2000 at 0 hours GMT". 

2) Galactic Coordinates:  an longitude-latitude system with 
   the line between the sun and the galactic center defining 0 degrees 
   galactic longitude. The plane of the galaxy defines 0 degrees
   galactic latitude. Galactic longitude runs 0 to 360 degrees, latitude
   -90 to +90 degrees. The positions of the galactic center and the
   plane of the galaxy have been determined thru about 100 yrs of
   observing. This coordinate system has the advantage that it is
   not tied to the Earth, so precession doesn't matter. And since the
   Sun tasks 250 Myr to orbit the galaxy, its motion doesn't matter 
   either.

>The position given in the posting was 0h 00.09 +0d 01'.7
>(2000.0). It appears that the first part (0h 00.09) is hours and minutes
>of right ascension, which would correspond to 0 degrees Aries in the
>tropical zodiac. If I'm correct, that's pretty wild -- it was discovered
>at 0 Aries! The rest of the position appears to be the declination
>(+0d 01'.7). The (2000.0) is the year 2000, which astronomers use
>as a reference point for measurements -- something to do with precession.
>
>Maggie

That position is not the discovery position. 1992 QB1 was discovered
on Aug 30 at position (RA,DEC)[2000.0] = (0h01m12.79s,+0d08m50.7s), neither
the position of the vernal equinox nor 0 Aries. The position Ms. McPherson 
quotes was the predicted position for Sept 15,1992 that is compatible
with the observed positions *IF*(!!!) the object has a circular orbit. As
of now, the orbit is *completely* indeterminate. More precise
astrometry is currently begin obtained.

My information on 1992 QB1 comes from International Astronomical
Union (IAU) circular #5611, dated Sept 14, 1992.

Marc Pound
Dept Of Astronomy
University of Maryland
mpound@astro.umd.edu

ps. Commendation to  Ms. McPherson for knowing that 2000.0 has "something to
    do with precession."