[AZ-Observing] Re: MM date limits (again)
- From: "Jones, Jack (AZ75)" <jack.jones@xxxxxxxxxxxxx>
- To: "'az-observing@xxxxxxxxxxxxx'" <az-observing@xxxxxxxxxxxxx>
- Date: Thu, 18 Mar 2004 12:45:22 -0700
Although I don't like the definitions much since they are "ground-oriented",
I like the references to the visibility of the horizon - civil: horizon is
clearly defined - nautical: horizon is indistinct. It's a continuum of
course, but I will try to memorize what the horizon looks like when a target
object goes invisible as a reference to warn how much time I have to play
with. (I'm also going to be running Starry Night on the notebook in real
time.) But usually I freak at the end of astron. twilight when first light
shows and I have 20 left.
Jack
>
>
> The 10 degrees was a sort of arbitrary choice, chosen as a
> time when M30
> would be several degrees above the horizon. I do remember
> looking at M30
> in 2001 in very bright twilight. I could see scopes and cars
> clearly at
> the other end of the field. I would guess it was well past nautical
> twilight when we saw it.
>
> In any event, I don't recall the distant mountains presenting
> nearly as
> much of a problem for seeing M30 as the horizon extinction and sky
> brightness.
>
> Tom
>
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