Re: [Phys-L] Ex: celestial motions

["Albert J. Mallinckrodt" <ajm@cpp.edu>]

> On Aug 13, 2019, at 7:50 AM, John wrote:
>
> You guys are using similar words to describe two different things:

Fair enough. My response was motivated primarily by Anthony’s statement that “the
Moon appears to move much faster across the sky,” which suggested that he was contrasting that apparent motion with the Sun’s “one diameter in two minutes” motion of the previous paragraph. 

Summary: The moon moves “much faster than the Sun” relative to the stars” and “a little slower than the sun” relative to the horizon.
> > On 8/12/19 10:12 PM, Albert J. Mallinckrodt wrote:
> > The moon and the sun both “move” their own diameters in about 2
> > minutes.              [a]
>
> > On 8/12/19 6:37 PM, Anthony Lapinski wrote:
> > [the moon] moves its own diameter across the sky each hour. [b]
>
> I say [b] refers to the moon's motion relative to the fixed stars.
> Roughly 0.5/(360/28/24) = 0.93
>
> Meanwhile [a] refers to sun or moon's motion across the sky,
> relative to the meridian arc.
>
> > Sunsets appear to take  longer
>
> They *do* take longer, because the sun generally does not set
> perpendicular to the horizon. It does twice a year at the
> equator, but never in temperate or higher latitudes. At the
> north pole, sunset lasts more than a day, and happens only
> once a year. At lesser polar latitudes, you get multiple
> sunsets per year, each lasting many hours.
>
> > I think solar/lunar
> > eclipses take about an hour to progress from start to totality.
>
> That depends.
>
> A partial lunar eclipse might last only a few seconds from start
> to finish, if the moon merely glances the earth's penumbra.
>
> A solar eclipse is a completely different animal. Much depends on
> your viewing location, relative to the center of the track. If the
> eclipse is central at your location and high in the sky then yes,
> the whole thing lasts roughly two hours from start to finish --
> which is a corollary of item [b] above.
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