Made it back to London after a fairly uneventful flight back. We did head into downtown San Francisco, but as I was terminally sleep deprived I’m afraid it seemed like a dream. A dream featuring a world famous prison, so par for the course really!

One of the memories of Mauna Kea that sticks is the sight of a gorgeous halo around the Moon. While not exactly rare, it was the first time I’d seen something like this with the Moon overhead, and it was a deeply erie experience to be standing underneath this ring of light. A sci-fi director’s dream to say the least!

It seems from the Sky at Night mailbox that haloes have been common in the UK over the last week or so, too, so for the record the explanation is due to ice crystals in the upper atmosphere. The hexagonal shape of the crystals refracts the light by 22 degrees, which is the radius of the halo.