[time-nuts] reply re Harrison's timing method - #13 in Vol 176, Issue 44 digest

[Adrian Godwin]

On Wed, Mar 27, 2019 at 2:00 AM jimlux <jimlux at earthlink.net> wrote:

>
>
> To get 1 second accuracy, you need 360/86400 = 0.004 degree
> measurements. That's 0.073 milliradian - 1 cm  at 140 meter distance.
>
> I'm not sure an "edge" is sharp enough (diffraction, etc.), although
> your eye is pretty good at "deconvolving" the linear equivalent of an
> Airy disk/rings.
>
> A small telescope and a camera might work, lining up with the two edges
> as a "fixed offset knife edges".  It could also work in day time (you
> can see Polaris in the day time with a 28x telescope with a 1" objective
> - a surveyor's theodolite)
>
>
If I've calculated it correctly, I think that's about 1 pixel width on a
24megapixel APCS DSLR with a 55mm lens, which is easily achievable. It
would be nice to have 10 pixels to  find the true centre, but since the
star's location will move predictably across the entire fov, it should be
possible to interpolate very effectively.