Is this natural, seems to me like a hair.

[Nicola Hannah Butterfield]

I have this hair like feature in two images, imaged months apart, I find it strange it would be in two separate image sequences, but only the two, of complied images of the moon I have done seem to show it.

If one evening, maybe, other images I have are lit as the moon is waning. So if it is a cliff, they wouldn't show it

[vlaiv]

Google moon screen shot:

See also:
https://en.wikipedia.org/wiki/Rille

[Knighty2112]

Rupes Recta. Otherwise known as the straight wall.