|By far the most work done at KPO is development of the
control systems rather than actually using the telescope! However
occasionally it does get used for its intended purpose and provides
useful data for scientific analysys.
When we had the C14
in the observatory we recorded a fair amount of data with our Optec photometer in
semi-automated mode. This meant choosing a target to observe ourselves,
giving the software a bunch of observing parameters and letting it go.
Data acquired at KPO during this period has appeared in various
scientific papers. We aim to do this again at some stage possibly using
CCD technology instead.
Using our recently commissioned video camera we have been able to
record a few of these events where a minor planet (aka asteroid) passes
in front of a star causing the star to apparently dim to the brightness
of the minor planet for a few seconds. When several observers in
different locations record the timing of these events the position,
size and even shape of the object can be determined.
In the past this has been quite difficult to do accurately because of
the human factor in timing or the sensitivity of the instrument when
taking samples fast enough to be useful. 10 samples/second is the bare
minimum that is useful and our photometer is simply not sensitive
enough to see down to 10th magnitude unless it is integrating over 10
||Our very first successful recording of an event
by video was actually quite technically challenging because the
expected magnitude drop was only 0.2 magnitude - pretty much impossible
to detect visually.
On the left is an example screenshot from the video. Apart from the
on-screen display, every other frame looks identical. The dot in the
near-centre of the frame is the magnitude 9.3 asteroid Fortuna.
Information about how we got the on-screen display in the instruments
||However when the video is processed using a
photometry technique (comparing the amount of brightness in a small
circle where the star is with the amount of brightness where the star
isn't) the brightness of the star dims very slightly yet unmistakably.
The graph has been vertically exaggerated to highlight the effect of a
drop in the mean from 3500 to 3100 for nearly 30 seconds.
These happen when the moon passes in front of star in such a way that
the star appears to skim along the edge of the moon, disappearing
behind the lunear mountains and re-appearing again. This supposedly
helps in mapping lunar mountains. This is another good candidate for
The image on the right is somewhat uninspiring
vidcap of the lunar limb just before a star disappears (the star is
just visible a a dot about 1cm from the moon). Click on the image for a
short mpg of the 2-second disappearance behind a mountain. There was
wispy cloud during this event just to make things worse. The star went
behind a second "wider" mountain a bit later in this particular event.
Given that the moon is extremely bright and the star is magnitude 6, it
is quite tricky to capture an event like this because of the limited
dynamic range of a video camera. This is the reason why the moon has
been banished to the corner of the frame as much as possible so the
camera doesn't automatically reduce the exposure and render the star
|There is probably little value in in lunar occultations now days since
it only really helps confirm the predicted position of the moon -
something which is well known from other methods now. However,
occasionally, the moon goes in front of "interesting" things which is
kind of interesting to watch if nothing else.
re-appears from behind the moon.