Last updated: 19 May 2002

Subject:	ETX90RA, Mercury monitoring.
Sent:	Saturday, May 18, 2002 14:45:49
From: (martyn)
Hello all,

For the past couple of weeks I have been observing Mercury. I have
seen it sling around the sun and come our way. Watching it become
brighter and dimmer again and see it getting lit more and more "from
behind". The observations were conducted after I had collimated my
Below are notes which I took from my logbook. I hope you can make
sense of them....

observing from the Netherlands
52 40.30 N
 5 56.10 E

25 April 2002, 19:40h UT, altitude: 8 degrees, clear with slight wind.
SP 6.4mm
Disc clearly seen, phase is clearly seen too. Looks slightly more than
50% lit, actual is 64% lit. Heavily affected by atmospheric
refraction, northern horn was green and southern horn showed red. Due
to the less than perfect seeing the green and red on the horns were
quite smeared out.

1 May 2002, 19:40h UT, altitude: 12 degrees, hazy clouds on NW
horizon, no wind but air not still.
SP 6.4mm/UWA 4.7mm(yes, really)
SP6.4mm: Looks clearly less than 50% lit, actual = 44%. Seeing boils
the image a bit but crescent of Mercury is clearly seen. No
atmospheric refraction is yet visible.
UWA4.7mm: Image a bit duller as I viewed Mercury through this thin
cloud. Mercury's "half moon" clearly seen. In steadier moments, the
phase of Mercury is visibly JUST less than 50%...noted this at 19:53h
UT, alt: 10 degrees.
At 19:50h UT, I thought I had noticed the beginnings of atmosperic
refraction, a slight coloration on the horns, but I was not certain.
At 19:55h UT, seeing really begins to interfere with Mercury's
visibillity and at 19:57h UT atmospheric refraction had defenitely

2 May 2002, 19:30h UT, altitude: 13 degrees, sky partly clear(the
right part) and very clean, VERY windy. The wind really rocked the
SP6.4mm/UWA4.7mm: Found Mercury at 19:30h in the Jena 10X50. Through
the etx in both ep's the "half moon" was recognized but very ill
defined. phase is 41%.  Seeing is very poor.
SP15mm: 20:00h UT, altitude: 9 degrees, crescent shape(tiny) even
recognized at 83X!

7 May 2002, 19:25h UT, altitude: 14,5 degrees, phase = 28%, some haze
in NW sky, seeing not very good.
PL12.5mm: The phase of Mercury (28%) was sort of recognizable, I
viewed through a thickening haze.
UWA4.7mm: From 19:27h UT I viewed Mercury through the UWA4.7mm.
Through thick haze and poor seeing the planet was seen to be a
crescent, lit for about 1/3. Image was wobbly and vage. As I viewed at
266X, the haze was thickening further until Mercury was rendered
unviewable and lower powers did not help either.
At 20:01h UT, Mercury back, altitude: 9,5 degrees, UWA4.7mm:
Looks very mushy. At 20:03h UT I recognized the crescent again. At
20:05h UT I clearly noticed atmospheric refraction on the mushy
At 20:07h UT I inserted the SP6.4mm to get a brighter image as the
planet was now getting dimmer due to thickening haze/clouds. Crescent
shape confirmed but seeing and transparancy very poor. Low altitude,
atmospheric refraction now very apparent. Thickening clouds now cover
Mercury permanently.

9 May 2002, 19:43h UT, altitude: 11,5 degrees, phase = 23%.
19:43h UT, SP15mm: The crescent shape of Mercury is seen at 83X, very
thin, looks like first quarter moon. Start of atmospheric refraction
is visible.
19:57h UT, UWA4.7mm: Crescent of Mercury quite well visible!
Atmospheric refraction does not degrade image a lot.
20:00h UT, SP6.4mm: Crescent clearly seen, atmospheric refraction
too...not too bad though. I could still find Mercury in the 10X50's.
PLanet is clearly less bright than a week ago.
20:05h UT, SP9.7mm: Crescent seen, seeing interferes now and
then...partial bloathing of the crescent. Crescent shape clear
20:06h UT, sp6.4mm: Seeing plus low altitude(8,5 degrees) destabilizes
image at 195X. Crescent bit mushy.
20:30h UT, SP9.7mm: There seemed to be very little haze left at the
planet's current altitude - 5,5 degrees and the air seemed more stable
too as the crescent could clearly be recognized.

12 May 2002, 19:24h UT, altitude: 13 degrees, phase = 16%, clear,
practically no wind.
Found Mercury in the SP26mm with the help of settingcircles...jumping
of Venus.
The planet was not easy to find as contrast with skybackground is low.
But...when I did find Mercury I could see it's TINY THIN crescent at
SP15mm: At 83X the crescent was very clearly visible. The seeing in
the upper atmosphere dimmed the image of the planet now and then.
19:30h UT, SP9.7mm: Mercury's thin crescent (alt: 12 degrees)
beautifully seen. Seeing bloaths the image, i.e. with apparent, more
or less regular intervals a "bright bubble" seems to traverse the
crescent from southpole to northpole of Mercury.
Atmospheric refraction is not apparent.
19:33h UT, SP9.7mm: Crescent clearly seen, contrast with skybackground
still bit low. Limb boils a bit.
19:35h UT, UWA4.7mm: Contrast low, but tiny crescent now "looms large"
in the eyepiece.
Seeing effects were visible, but they did not really degrade the
crescent-shape of Mercury at 266X.
19:37h UT, UWA4.7mm: At 266X, the "disc" of Mercury (alt: 11 degrees)
is actually quite substantial, the crescent gives a good idea of it's
size in the eyepiece.
19:40h UT, SP9.7mm: Crescent well seen, in spite of the seeing
distorting the image at moments.
19:45h UT, UWA4.7mm: Better contrast now. Crescent still easily seen.
Seeing induced atmospheric refraction now clearly apparent.
20:00h UT, UWA4.7mm: Crescent seen, atmospheric refraction now quite
apparent! (alt: 8 degrees).
20:07h UT, SP15mm: crescent can be seen quite easily.
20:10h UT, SP6.4mm: The SP6.4mm also still shows the crescent fairly
well. Atmospheric refraction present.
20:13h UT, UWA4.7mm/SP9.7mm: A LOT of atmospheric refraction! (alt:
6,5 degrees) Image now also getting mushy at 266X. At it's present
lower altitude, some haze is present. The SP9.7mm still shows the
crescent quite well.
20:18h UT, SP6.4mm: Crescent at 195X also mushy, a lot of atmospheric
refraction. Crescent somewhat recognized nevertheless.
20:20h UT, SP9.7mm: Crescent bit easier recognized, but far from well
defined. (alt: 5,5 degrees).

A couple of days without clear view of the W to NW horizon followed,

16 May 2002, 19:45h UT, altitude: 8 degrees, phase = 9%(nine percent),
clear, no real wind, only a whisp of cloud on the NW horizon.
Found Mercury with the help of the settingcircles, with Venus as a
base. I found it in the SP26mm. Contrast with the clear skybackground
is low.
A quick succession of different-power views follows.
SP15mm: Crescent-shape readily apparent, VERY thin crescent...9%.
SP9.7mm: Shows crescent a bit better.
SP6.4mm: Decreases contrast even more, but crescent shows. However,
seeing makes abit mushy.
UWA4.7mm: Shows crescent - sort of mushy. Difficult to track manually,
contrast in eyepiece low. Takes a bit of concentration.
20:00h UT, SP9.7mm: The seeing interferes heavily. Altitude is less
than 6 degrees.
20:08h UT, SP9.7mm: Atmosperic refraction noted.
20:11h UT, SP9.7mm: Image now deteriorating badly. Crescent no longer
properly defined, still crescent-like though. I viewed through haze at
this time, altitude is just over 4 degrees!!!

If only I had a clear horizon 1 or 2 days after the 16th, I might have
been able to spot an even smaller phase of Mercury. But on the 16th it
was allready not so easy to see the planet. Once I had it in the
eyepiece (4.7mm too) I could see it through thin passing haze/cloud as
well. But tracking manually was difficult due to the very low contrast
between the 2.7 magnitude planet and a bright evening skybackground.
It was a lot of fun watching Mercury come around the sun this way.

observing from the Netherlands
52 40.30 N
 5 56.10 E

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