[time-nuts] Re Danjon Astrolabe
Dr Bruce Griffiths
bruce.griffiths at xtra.co.nz
Wed Sep 27 20:45:58 EDT 2006
> Brooke Clarke wrote:
>> I'm interested in automatically measuring the earth's period by looking
>> close to straight up with a fixed telescope.
> This sounds like an interesting project. I've been looking for something
> to do with the Meade 4455D telescope I just got. (D=114m F=910, f/8)
> Doing a fixed mount at a know location shouldn't be a problem. I've also
> got an untested Hamamatsu E717-07 photomultiplier tube. Please let me
> know how it goes.
> time-nuts mailing list
> time-nuts at febo.com
The aperture of your Newtonian telescope is a little too small for this
application especially in the daytime.
You need to use an IR filter to block most of the Rayleigh scattered
You will also need to have good baffling and use a Lyot stop to block
With an aluminium tube focus will not be stable as the temperature changes.
If you have a plate glass mirror then a steel tube will give a much
better match to the mirrors focal length temperature coefficient.
Shading the telescope tube and mirror from direct sunlight is also
essential to avoid heating the tube and creating large tube currents
which will severely degrade the images.
More information about the time-nuts