Diamond Dust


Similarly to how the moon halo is created by ice particles in the cirrus cloud, the ice particles suspended in air (typically relatively close to the ground), called Diamond Dust, can also create halos, as well as moon dogs (bright points on the halo to the left and right of the Moon).

To create the halo, ice crystals suspended in air have to be of a particular shape (long cylinders with hexagon base) and aligned in a particular orientation. The light passes through two side faces of the crystal and is refracted between 22° and 50°. Similarly, for the moon dogs to be visible, specifically shaped ice crystals need to be present (these need to be hexagonal shaped plates), and they have to be in horizontal orientation. Also visible in the picture are light pillars (both above and below the moon, as well as created by the artificial lights on the buildings). These are also created when hexagonal plate shaped crystals are in the air – the light reflects off the base (or the top) of the crystals creating the visible vertical “shafts”.

In the foreground the Met Tower is visible (to the right of the Moon), with an array of sensors attached: sonic and prop-vane anemometer, laser precipitation sensors and snow depth sensors, all attached to an automatic weather station also installed on the mast. To the left is a Stevenson Screen which hosts four thermometers used for calibration readings. Next to the Stevenson Screen (on glacial poles to either side) are temperature and humidity sensors, also connected to the automatic weather station installed on the mast.