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at the other end of the scale, can someone please explain earthshine? you normally only see it just before sunset on a very new (or old?) moon. Is there such a thing as a night moon only illuminated by sunlight reflected from the earth? I know that would be a total solar eclipse but does earthshine happen all the time during a new moon and we only see it at dusk?
You've got it right: you see it just after sunset on a new(ish) moon. If you were up early enough I expect you would also see it just before sunrise on an old(ish) moon as well. For work-related reasons, I suspect most people are generally too busy to look/notice at that end of the day. Or, like me, in bed.
You would not see earthshine reflected off the moon unless it is just above the western horizon (in the evening) just after sunset. That's because at that time, anyone on the moon would be able to see a "full earth": the whole illuminated hemisphere of the earth's surface is pointed towards the moon. That casts the most "earthshine" onto what is mostly the dark side of the moon. If the moon is high in the sky at night, the dark side o the earth would be pointed towards it so there would be no earthshine.
Summer full moons tend to be far less spectacular than winter ones. There's nothing magical about the phases of the moon - they are really not very interesting at all from a geometric/astronomic point of view (n.b. I am no astronomer). A full moon is simply the closest it gets in its 29-ish day cycle to being diametrically opposite the sun from the earth's point of view, so in the winter, when the sun disappears a very long way below the horizon, the full moon will be high in the sky and will look very bright. In the high summer, when the sun just creeps below the horizon but its influence, even in southern England can be seen all night long, the full moon must be correspondingly close to the horizon as well.
The Dunwich Dynamo ride is geared to be on the Saturday night nearest to the full moon in July. When it is very early in the month, ie less than a fortnight after the summer solstice, that full moon is the lowest in the sky of the entire year.