Is a filter necessary when observing the Moon during the day, and if so which?

Thanks!

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No filters are necessary to safely view the moon during the day even with a large scope. Only a very small amount of the suns light is reflected off the moons surface. When I've observed the moon during the day with my scope I've found the views better without any color filters or a "moon filter" due to the fact that my eyes are not dark adapted and therefore the moon does not appear as glaringly bright. Hope this helps..

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Thanks for the response, orangeSCT. Actually it was not the safety aspect I was so interested in. I was just wondering whether a filter would improve the contrast between the Moon and the bright background, or enhance the definition. :-k

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Under some conditions a polarizing filter, suitably oriented, can help somewhat in the contrast department. This works best at reducing sunlight scattered in our atmosphere when the sky is clear and the moon is near a quarter phase (scattered light is most strongly polarized at 90 degrees). The sunlight scattered off the moon is also polarized, but not as much (since a lot of the light makes multiple bounces in all those tiny dust pores before comg back at us). Fortunately it's easy to test this by pulling off a pair of polarizing subglasses and twisting them around.

(I did this demo for a grad course once when we talked about polarized light, mostly as a break. We had one student from a country where they are apparently still quite rare - he was utterly fascinated and it took me a while to get the shades back. Well, when you're reminded fresh that way, the phenomena are fascinating.)