[foxyv]

Cosmic rays are not exclusively associated with the sun. There are a lot of Galactic Cosmic Rays still. It's pretty much leftovers from supernovae, black hole mergers, neutron stars, accretion disks and such. But yeah, at night would be better.

Edit: Correction, there is very little difference and fewer cosmic rays during the day. Source: https://arxiv.org/pdf/physics/0105005.pdf