Re: [Phys-L] Ex: celestial motions

[John Denker <jsd@av8n.com>]

You guys are using similar words to describe two different things:

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.