USER OBSERVATIONS Last updated: 13 January 2003

Subject:	Shadows on Jupiter (ETX90RA)
Sent:	Saturday, January 11, 2003 13:09:28
From:	martyn@starmail.co.za
Hello all,

yesterday (10 Jan 2003) I had a wonderful view of two shadows close
together on the Jovian disc.
At 20:10h UT I slung the ETX in the softcase around my neck and cycled
through the snow to a nice dark observing site where a picnic-table was
awaiting me and my ETX.
At 20:20h UT I had the scope set up and noticed the thing had to first
cool down. The scope was brought from an indoor 20 degrees C to a minus
8 degrees C. It had been clear all day, but on arrival some clouds had
moved in and my observations of the shadows were done through hazy
openings in the clouddeck.
At around 21:00h UT through the SP15mm(83X) I noticed a dark spot in
between the SEB and NEB on it's way to transite the Central Meridian.
The other shadow was still hiding in the poor telescopic seeing.
At 21:45h UT, through the SP6.4mm I did notice both shadows. One from Io
and one from Europa, the shadow of Io was the one I noticed first. It
was much darker (larger too) then the shadow of Europa! The shadows were
very near one-another with the shadow of Io being ahead of Europa's
shadow.

I followed the shadows as they transited the Central Meridian at around
22:00h UT. At about 22:10h UT the shadow of Europa had passed the
Central Meridian also, and at 22:20h UT I noticed very clearly that the
distance between the two shadows had increased, they were no longer very
close to one another.
Io had clearly moved ahead of Europa.
I followed the shadows until 22:40h UT. The moons themselves were not
visible as they were in front of the disc of Jupiter.

I find it quite wonderful that such a simple observation actually
results in learning about solarsystem objects. In this case Io moving
through space faster than Europa does.


regards,
martyn
observing from the Netherlands

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