The night sky isn’t perfectly dark—instead it glows faintly, and the source isn’t exactly local. ... A decently dark site in a rural area has a sky background of about 21 mag/arcsec 2.

As the technique suggests, she moved the light similar to “painting” so that the building is evenly lit. The now, brightly purple building stands out against the grey darkness of the cloudy night.

A glowing, swirling spiral of blue and purple was seen across the UK and also in parts of Europe on Monday night. But what was it? The cloud-like shape appeared for several minutes before ...