Mir seen at -0.8 degree?

Ron Lee (ronlee@pcisys.net)
Sun, 29 Dec 1996 10:21:48 -0700 (MST)

I just went out and did my best to determine the actual
horizon for the setting point for the Mir observation
yesterday.  I measure it to be approximately -0.4 deg.
This was done using a level and then coming home and
recreating the angle observed, then measuring and
calculating by simple trig.

Estimated angle of the cloud bank above the horizon
(disappearance of Mir) is 0.2 degree.  Thus (ignoring
the errors) the observed elevation of Mir was about
-0.2 degree.  This means that is was below my true 
horizon (elevation = 0 deg)

Assuming a refraction angle of 0.5 degree yields an
actual elevation of -0.2 minus 0.5 equals -0.7 deg.
This is consistent with the values calculated by
STSPLUS and SKYMAP using post-burn elements.

I am using the term "elevation" to represent vertical
angle from the horizon, where the local true horizon 
is 0 degrees and the zenith (overhead) is 90 deg.

To make this obs, I travelled to a point about 1 mile
SE of my normal location to improve the horizon.

It may just be a matter of semantics, but I am assuming
that the elevation that would be appropriate for use
in deriving element sets would be the -0.7 deg value.

This obs was relatively easy due to the favorable horizon
and the clear air at this altitude.  There are places in the 
mountains to the west where gaining altitude (height above
sea level) would improve the horizon (make the value more
negative).  Pikes Peak is approximately 7000' higher than 
my location.  I do not know what improvement that would

A salient point to this obs, beyond just a personal challenge,
is that people should not discount low elevation passes for
seeing interesting objects, especially Mir and the Shuttle.

I blew off the last shuttle mission due to its 28.5 deg inclination,
yet a local observer (David Brierly), did see it easily on at
least one occasion.

Ron Lee