Solar eclipse

[north star]

What is the reason for the length of time of totality roughly a few minutes, during a total solar eclipse. It appears to me that the moon gradually occludes the sun, conveniently waits a few minutes at totality and then moves off again.

[Clanad]

Your perceived observation is obviously , an optical illusion. The umbra of a total eclipse is only about 100 miles wide. The chances of being inside of this area is fairly small, considering the amount of the earth that is either inaccessible or on the high seas... intuitevly, you know the apparent speed of the moon is a constant and doesn't "stop" during the corona producing stage of the eclipse...

[mibn2cweus]

The duration of totality for a total eclipse as seen from the ideal location varies from seconds to up to about 7 1/2 minutes depending on the mutual distances of the Sun and Moon from Earth during a specific eclipse.

compare totality duration times of several total eclipses here

[heathfield]

The Earth's elliptical orbit means that the distance to the sun varies over the course of a year. Though we aren't aware of it, this means the sun's image can be bigger or smaller at different times.
Since the moon's orbit round the Earth is also elliptical, its image can also be bigger or smaller.
Because of these changes in size, the moon's apparent diameter can be up to 7% bigger than the sun's. When this happens, it seems to take ages for the totality of an eclipse to pass. Conversely, the moon's diameter can appear to be almost 3% smaller than that of the sun. Then, the eclipse seems to last for only seconds.

[R1Geezer]

It's the time spent in the umbra and it varies according to various factors, not least of which is the Earth rotating at about 1000mph, then of course the moon is also moving etc etc. It does not wait, when you are under totallity you start at one side of the moon's shadow and 100 miles of moon shadow passes by you giving the illusion that the moon is hanging about.

[north star]

Guys, my thanks for that.

A follow on question :- is there any reason other than serendipity, that the diameters of the sun and moon, as viewed from earth should be about the same?

[heathfield]

It just happens to be. Nobody designed them that way.

[R1Geezer]

yes it's pure coincidence that the daimeter of the sun is roughly 400 times bigger than the moon and roughtly 400 time further away. How fortunate we are!