It had been incredibly dry and clear when I'd arrived at the mountain top, but while we were familiarising ourselves with the telescope during the afternoon before our run started, the weather sensors were showing that the humidity was steadily rising. Outside, the clear blue skies were turning grey. The cause was the Kalima, a hot wind carrying dust across from the Sahara. By the time the sun set, the atmosphere was so dusty that you couldn't tell where the horizon was.
I thought this would ruin our observations, particularly as it was full moon. But we could still find our objects, and at the huge magnification of the 2.5m telescope, the bright background wasn't really a problem. So we observed. I went out during the night to see what I could see, but only bright stars were shining through the murk.