Tuesday, October 21, 2014

Mars and Siding Spring

Ben Davidson put out this video last evening:

I immediately emailed him back with a response, explaining everything that he was seeing (and speculating about) except one series of images which I'm still baffled by (although I'm leaning toward an optical effect).

No response, and as of his latest video this morning, he's either ignored my email or not seen it.

Anyhow, here is my email to him in the hopes that he'll see this blog entry:

Ben -- I've been an observational and theoretical astronomer for 35
years.  All of the things you show on your video are things I've seen
before except one.  Let me go through it all in some detail:

00:34 - 00:37 Those donut shaped objects are NOT caused by the
atmosphere, but rather internal reflections in the optics of the
telescope.  The atmosphere causes stars and other non-resolved objects
in the sky to twinkle, but that wouldn't be detectable in these
images.  The donut shape is actually an image of the primary mirror of
the telescope with the secondary mirror blocking the center (the
"hole" in the donut).

00:50 - 01:34 All optical effects.  Optical coatings create some very
beautiful effects like this.  Seen 'em a million times.,,

01:35 - 02:00 more about this below

02:00 - 02:37 this is the one you're most confused about, but it's
obvious to those of us who have used cameras on telescopes what this
is.  In order for the camera to see the background stars, a fairly
long exposure needs to be taken (in this case I'd guess it's about one
second).  The camera, of course, is in "live" mode so it's just
shooting pictures continuously and displaying them -- but not at video
rates otherwise we wouldn't see those background stars.  The next two
frames that distort the image of Mars is the telescope slewing while
the exposure is being taken.  This causes the streaks and blobs that
you see.  While the telescope is slewing, there really isn't anything
interesting to see so they cut the feed.  I've attached some data
images ('boops') I've taken of the Jupiter system (for my photometry
work) where I've bumped the telescope while an exposure is being
taken.  As you can see -- the same "mysterious" extensions.  Jupiter
is overexposed but you can see the effect on the moons.


Here is more proof.  Look at the attached image named 'mars3'.  These
are two images taken from your video tonight.  In both images, there
is a 'TOP' blob, and a 'BOTTOM' blob.  First notice that the distance
between the TOP blob and BOTTOM blob is the same in both images --
indicative of the same exposure time.  Also notice that the position
of the BOTTOM blob on the left image is in the same place the TOP blob
on the right image.  This means the telescope was slewing at a
continuous rate (as expected).


So no big deal -- I'd probably do the same thing and show people
something else other than the telescope slewing.  I hope my
explanation makes sense.

The one that sorta has me baffled is the image from 01:35 to 02:00.
The bright object in the middle of the field of view not only is
flickering like I haven't seen anything astronomical flicker, but it's
also moving against the background stars.  In the short time span that
this apparently covers, we would NOT see Mars move against the
background stars.  I can't account for the flickering at all, except
to say that maybe it's some kind of off optical effect (it usually
is).  Do you have any information on how this video was taken????

Hope this clears up most of it.

Great work.

Peace, CL

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