金星 ALPO-Japan Latest
Venus Image 2007/09/13(UT)
Arnaud van Kranenburg
Arnaud van Kranenburg(235mm SCT)|
I have seen many activities on the dark side of Venus now that the
planet was so well placed for Europe. I have imaged the planet too and
was able to record the thermal glow of the planet on three occasions (or
four, but the first way more of a try-out). I have attached my results.
Although there seems a hint of detail on the surface, I am very careful
assigning these to some surface features in the NIR. I believe it is
more likely that these are caused by the image distortions of the bright
dayside. It seems I have had some trouble with internal reflections. I
solved this partially by making separate series of recordings with the
camera rotated at different angles, which seems to cancel the
reflections out. But it was impossible to get rid of them completely, so
I am careful.
The images were made using a 990 nm longpass filter, which I believe is
identical to the one Ikemura used. Even then, the dayside is
overwhelmingly bright. It would be nice if we could find a solution for
that at the next opportunity.
Because of the rather early date, was able to capture Venus while it was
still a small crescent. Still, on the four occasions I observed, no
visual observation could be made of an Ashen light. I must stress though
that I am by no means a very skilled visual observer, but more of an
imager. Still, if the Ashen light were obvious by any means, I feel that
I would have seen it.
As David already pointed out, I would like to make a strong distinction
between the Ashen light and the thermal recordings I made. On the 13th,
I made recordings in the NIR at >990 nm. Between session, I also made
recordings in the green light, although with a shorter shutter because
Venus is much brighter in the green light. Even though the planet is
oversaturated (but clearly recognisable as a crescent), no nightside can
be made out. Similar images at >990 nm show the nightside very clearly.
I think that, if the Ashen light were visually observable, it should
have been recorder on these highly oversaturated images.
Therefore I think that there is no link between the thermal radiation
and the Ashen light. Both are different phenomena. Also, on the 13th
there was no sign of the Ashen light in the green light. Since green as
the most eye-sensitive visual wavelength I think this demonstrates that
no visual Ashen light was present at September the 13th. If it exists, I
believe it must be a temporal phenomenon.
Recordings of Venus on the 23th showed no hint of the Ashen light in UV
and > 807 nm NIR. But I made no attempt to overexpose because I felt the
dayside's cresent was already to bright to pick up the thermal
I hope this additional info will attribute to the discussion.
[Arnaud van Kranenburg:Vlaardingen Netherlands]