Claire Baxter (Member 60,827) was lazing in the sun in Wisley, Surrey, England when she spotted some celestial geometry in the skies above. The bright arc above the Sun is part of an optical effect known as a circumscribed halo. This formed as sunlight was bent, or refracted, as it passed through the ice crystals in the milky layer of the high cloud Cirrostratus.

If enough of the right sort of ice crystals are in the sky, a circumscribed halo can extend right around the Sun, appearing as a sort of distorted oval, the shape of which varies greatly with the Sun’s elevation. Here, the ice crystals in the Cirrostratus creating the light effect would have formed ahead of a weather front – probably just a weak warm front, bringing some cloud cover the following day. This front would have introduced the moisture high in the sky, which was also responsible for these two aircraft condensation trails to persist. Like some celestial blueprint for Claire to survey, these arcs and lines of the sky were charting the atmosphere’s plans for the weather later that day.