Our next stop, appropriately, is the Gobi Mirage ger camp; this part of the desert reliably delivers the conditions that make shimmering lakes and seas appear in the distance, over dozens of miles.
Normally, the Earth's atmosphere has a vertical temperature gradient of about -1° Celsius per 100m - it gets colder as you go up. When there is strong heating at the ground level, the temperature gradient can reach -4° or -5°C per m. Cold air is more dense than warm air, and therefore has a greater refractive index. When light rays pass from hotter to cooler air, they bend in the direction of the gradient; if the air near the ground is warmer than that higher up, the light rays bend in a concave, upward trajectory. Once the rays reach the viewer’s eye, the visual cortex interprets them as if they traced back along a perfectly straight 'line of sight', i.e. at a tangent to the path the ray takes at the point it reaches the eye. The result is that an 'inferior image' of the sky above appears on the ground. The viewer - especially a thirsty one - may incorrectly interpret this image as a body of water reflecting the sky, which is to the brain a more reasonable occurrence.
We reach the Gobi Mirage camp; the cooks bring out airag in greeting. As we walk towards our ger, a small cloud of dust tearing over the desert resolves itself to be another SUV; it stops at the edge of the camp, and two gesticulating figures jump up and run after us; 'Zaya has arrived.
When Byambe phoned in her intention to quit, 'Zaya, the President of Blue Silk travels in Ulaanbaatar, called her sister, jumped into a SUV, dropped off her 5-year-old Naran with her aunt, and, driving madly 15 overnight hours non-stop over the middle- and south-Gobi, arrived helter-skelter at the Mirage camp to take over personally. Out went Byambe, back to the Land Cruiser, to lurch back to the capital. and in came the best guide we could ever hope to find for the remainder of our trip; 'Zaya and her Peace-corper husband Jon have an unique combination of perspectives, one an Mongolian-insider, the other an outsider who has slowly integrated into Mongolia.
In the afternoon, as we eat in the cooking ger, storm clouds roll in. Pea-sized hail-in-the-desert follows, and Mr. M runs around collecting them in my baseball cap.