Galadriel's Hair.

[Raynor]

Originally Posted by Rikae

why did Tolkien assign the gender of the sun and moon the way he did?

In Myths Transformed, Tolkien states that the Moon had a more combative role - against the night - thus warranting, to some extent, a masculine presence. By and large, males do seem to take a more martial role:

[The Moon] is to be a subsidiary light to mitigate night (as Melkor had made it), and also a 'vessel of watch and ward' to circle the world

Moreover, Arien, as the brighter light, seems more fitting, seeing that Varda is the valie of the stars. It is an interesting coherence in gender symbolism.