Summer in the central Arctic Ocean is usually overcast and grey, with low cloud or fog being present for more than 90 % of the time. Occasionally, however, the sun does come out, and when it does it can sometimes be spectacular.

8 September was the first completely clear and sunny day we have had since leaving Longyearbyen more than a month ago. We had beautiful clear light all day, but late in the afternoon got a spectacular treat – a halo with sun dogs (the bright spots either side of the sun).

Both the halo and the sun dogs are formed by scattering of sunlight by ice crystals in the form of hexagonal plates. These crystals are usually found in high level clouds, but can form at low level in cold regions. The halo forms at an angle of 22 degrees from the sun and is often coincident with the sun dogs, appearing to pass through them – this is the case here where the sun is very low, close to the horizon. If the sun is higher from the horizon, then the light passing through the crystals is skewed from the horizontal plane and the sun dogs move further apart.

A second pair of sun dogs formed at about double the distance from the sun of the first pair. While many of us have seen sun dogs before, no one on board has ever seen the second pair before – a rare treat!