[astroCS] vyzva k spolupraci na pozorovani prechodu Venuse cez slnecny disk

Jan Rybak choc at ta3.sk
Mon Sep 23 05:17:46 UTC 2002

Vazene kolegyne a vazeni kolegovia,

v poslednom cisle SolarNews (Volume 2002 Number 20, 18 September 2002)
bola publikovana vyzva k spolupraci na nasledujucom pozorovacom programe,
ktoru prikladam na konci tejto spravy. Rozsirujem tuto informaciu v domneni, 
ze by mohla byt zaujimava pre viacero pracovisk v SR a CR, kde sa pozorovaniam 
Slnka venuju. Ak nie, mozno aspon podnieti rozmyslat o vlastnych pozorovacich 
programoch, ktore by vyuzili  nie az tak casty jav prechodu Venuse cez slnecny 

Prijemnu pracu a slnecne pocasie praje

Jano Rybak

TL, 12/6/2002

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Venus and the Solar Limb Darkening

     >From Scholl-Faurobert <faurob at obs-nice.fr>
     >09 Sep 2002

Dear colleagues,

This message is intented to inform the solar community about a project that
we are starting at the Observatoire de la Cote d'Azur (France) and which
requires an international collaboration.


On June 8th, 2004 the planet Venus will transit the solar disk. This very
rare phenomenon will be completely visible from all of Europe and from a
large part of Africa and Asia; north and south America will observe the end
of the transit only. In Nice we wish to take advantage of this event to
measure the limb-darkening of the extreme solar limb for different spectral
bands in the visible. It seems that no such observations are presently
available! They would provide valuable informations on the density and
temperature gradients in the upper photosphere. Furthermore, the space
mission (France, Belgium, Switzerland) PICARD, will measure the solar
diameter in order to precise its variation with the solar cycle. Some
knowledge of the expected shape of the extreme solar limb is advisory to
prepare the mission.

A very simple observing set-up is being tested at the Observatory of Calern
(north of Grasse).

A monochromatic image of the full solar disk is formed by a small lense of
2.5 cm and recorded on a CCD camera operated by a PC. The transit of the
dark disk of Venus at the solar limb is followed with high temporal
resolution allowing a spatial scanning of a small fraction of arcsec of the
limb-darkening. The measurement is derived from photometric data which are
independent of the image distorsions due to turbulence in the earth
atmosphere, as long as the full image of the Sun is formed on the CCD frame.

More details will be given to interested teams.


Weather conditions are always uncertain, even in June in the south of
France; this is the primary reason why the same experiment should be carried
out at various places. Furthermore, independent measurements allow one to
increase the accuracy and reliability of the results. Due to parallax
effects , the transit of Venus seen from different locations on the earth
will intercept different solar latitudes, hopefully providing a set of quiet
and active regions.


We could provide some teams with the basic equipment needed for the
experiment (filters, lenses...). The guiding system and the controling PC
should however be available at the observing place.

We ask any interested persons to, please, send an e-mail to
faurob at obs-nice.fr or gay at obs-nice.fr , and we shall answer any questions
about this project.

P. Assus, M. Faurobert, J. Gay, J.P Rivet, J.L. Schneider


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