Star:
Struve 1937, eta Corona Borealis
Date & Time:
28 May 2003
Seeing: 7 <1-10
Seeing Scale (10 best)>
Transparency: fair
degrading to poor in lower sky
Location of site:
Annen, The Netherlands
53ºN, 6ºE
Site classification:
Rural with some light domes
Sky darkness: 5 <Limiting
magnitude>
Transparency:
<1 worst - 10 best>
Conditions: temp
10 C, damp
Telescope: C11 on
G11
Eyepieces: Pentax
SMC XL 40mm,
Ultima 30mm, TV plossl 20mm,
plossl 10mm, LV 5mm
Magnification: 560x,
400x, 280x
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I have observed Eta a few
times before, last year and this year, and it strikes me how easy it is
to split with the C11 when seeing is reasonable. With the predicted separation
of 0.55" confirmed by Steve's measurments I am always pleased to see the
obvious dark gap between the small airy disks at 560x, although the two
disks are surrounded by (parts of) several diffraction rings. This time
it was already with 280x that I had a positive indication of the two components,
where before I needed 400x. The color of both stars is white.
Another sub-arcsecond double
in CrB is Gamma. After the succes on Eta I had a (first ever) look at Gamma.
The separation of Gamma is
somewhat larger (0.7"), but the difference in brightness is also larger
(3.8 - 5.4). I suppose a DI of these doubles would be about the same. And
indeed at 560x Gamma was as nicely split as Eta. The bright primary creating
a larger image and the small, more faint secondary sitting close to it,
but not touching and showing a yellowish color.
Rating: 2
Ambience: The promise of
a clear night before Ascension day was reason to arrange an observingsession
in the field with two fellow-observers. On clear, moonless nights I now
and then go to a nearby location with a very low and reasonably dark southern
horizon. There I try to find all sorts of low objects that are invisible
from my home-location.
The location is only a few
minutes by car from my home, it's called "Eexterveld" (53-01 N, 06-42E).
It's a very high location, at least 15m... and gives a good view on the
horizon all around with absolutely NO direct lightsources in view (and
that's very special for open locations in this country)!
In the Netherlands we cannot
get around some lightdomes in the sky. In this case we have a major lightdome
in the west, caused by the small city of Assen, at 15 km's distance. When
the sky is real clear and dry the light of Assen causes no real problem,
except for objects directly inside the lightdome.
This night the sky was somewhat
disappointing. Besides the fact that we have already entered the grey summer
skies at our latitude, it remained hazy in the lower regions and there
was a lot of moisture in the air. I had to discard many of the low faint
fuzzies on my list. I had hoped to support Steve Bodin with his quest for
Double Galaxies but the situation was not good enough for serious observing
of the double galaxies that were on my list.
We started the night at 22.00,
still early twilight, but a good time to setup comfortably and to admire
the new C8 + Vixen GP that one of my fellow-observers recently obtained.
This time of evening the calls of a Quail (Coturnix coturnix), nearby in
the field, competed with the noise of passing trucks on the provincial
road a few miles away and the "roaring" of the motors of a 10" LX200.
Later at night the traffic
mostly died down, the quail went to sleep and the ambiance was mainly set
by the purring and calling of Snipes (Gallinago gallinago), now and then
a cry from a Lapwing (Vanellus vanellus) and the roaring motors of the
LX200...
We packed up by 02.30, our
equipment was dripping wet, the optics dewed up completely and the sky
was getting brighter again.
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