Horld Astrononv Dav (rAn) proiaet No3: ..Astroohwsicar
cosnological tests usino Flavitationai fenSeS_
Jean surdei(*), llare R.ry(*) and Hans Haubold(**)
*rnstitut
d'astrophysique, université de Liège, Belgiun **oot". spaee
Division, united Nations
and
Five observational projects associated nith
Days (HAD) ca-npaigr,(*) h""" been selected in
International Space Year. One of these projects concerns "Astrophysical and cosnological tests Ienses".
the lorld Astronony the context of the (llAD proj ect * g ) using gravitational
A short scientific description of this project, concerninEl trainly
the observational study of nicro-Iensing effects in the nell known gravitationar renses H1413+11? and 223?+o1os lrill be presented.
a
questionnaire nill be distributed to those astrononers possibly interested in participating actively in this project (observations,
data reduction, analysis and interpretation).
(x)
organized under theauspices
of
rsy/cosp AR/rau/Esa/NAsaIMPLICATIONS FOR TIIE STTIDY OF COMETS FROM NEAR.NUCI,EUS IIVTAGING
N. Thomas (Space Science Departnent/SI, ESTEC, IGplerloo'' L,22O0AGNoordwijk zh,
The Netherlands)
H.U. IGller (Max-Planck-Institut fiir Aemnomie, D-3411 lbtlenbr:rg-Tindau, C'ernany.)
The Vega 1,, Vega 2, aad Giotto missions provided remarkable observations of the nucleus of comet P/Halley and its irnrnediate environ-ent. Despite their limited d'rations, these
observations have deepeued our understanding of the cometarT nucleus, its surface
aetivity, and the production of gas and dust. The most obvious sxo"'ple of this concems
the albedo of the nucleus. At the time the "'issions werie conceived, cometary nuclei were
assumed to be highly reflecting,iq bodies. We now know they are darker than charcoai.
In this paper, we provide an overwiew of the results of the imaging systems and emphasize where the observations have assisted in ctnsolidating or modifring our concepr
of comets. Possible implications for the formation of the Solar System will aiso be
