From J.Lecacheux (provisional address : ol@ccr.jussieu.fr)

Occultations are the only way to obtain accurate diameter of transneptunians bodies (TNOs). These icy
asteroids orbiting beyond the outer planets are presumed coated with a very dark matter, but it seems that
exceptions could exist.At present time only diameters of the few biggest members, Pluto, Charon or the claimed
"new big" 2001KX76, have been measured. Pluto, transgressing the presumed rule, has high albedo, but maybe
this is due to seasonal snow deposits from its tenuous atmosphere.

On Oct. 25-26 around 1:26 UT (i.e. Saturday morning in Europe and Africa;
Friday evening in the Americas) the large TNO #15874 (still unnamed), alias
1996TL66, will pass very close to the magn. 8.7 star HIP 13530, alias SAO 93172. Owing to large ephemeris
uncertainties, occultation could occur from any place in Africa, Europe, s.America and a large part of
n.America.
(2000) coordinates are 2h 54m 15s.20 +13o 19´ 51".3, in a field of Aries easy to find with binoculars.
Details and maps from WinOccult are at the address

http://www.bitnik.com/mp/images/TL66.gif

Note that time uncertainty is several minutes, so the target star should be monitored from 1:15 to 1:35 UT.

Risk of missing the Earth is strong, so austral regions, s.Africa leading, will have a better chance than
Europe.

Note that a lot of TNOs are binary bodies with sub-arc sec. separation (already such 7 are known). If the mass
barycenter of such a couple misses Earth by south (as figured in the above mentioned web page), the north
component might cross Earth diametrally.

According to the Minor Planet Center the absolute magnitude of this TNO is +5.4 .If its albedo is 0.16, a
standard value for classical asteroids, then the diameter is 275 km and the occultation of next Saturday might
dure 12 seconds, as it is stated in the above mentioned web page. But if albedo is 0.04 only, a more realistic
value for cometary nuclei (we suppose), then the diameter is 550 km, and any diametral occultation should be
24 seconds long. So taking in account projection cosinus, occultation path wider than 600 km is plausible,...
if any occultation happens, of course.

15874 pertains to the "diffused class" of TNOs, a dynamically excited population characterized by large
orbital excentricities, significant inclinations and long periods. 15874 stays near its perihelion at present
time, at 35 astronomical units from the Sun, wich explains its easy CCD detection with small telescopes since
6 years (V=20.8). But its aphelion distance is 134 astronomical units, and its orbital period 774 years, i.e.
4.7 times longer than the neptunian one.

Clear sky to everybody.