With the sun only a long slit of light, the distortions in the atmosphere become visible as moving bands, parallel to the remaining slit of sunlight. They are usually very low in contrast and it helps to spread a white sheet on the ground to help viewing. They are VERY difficult to photograph. We've never seen any pictures of shadow bands. Of course, this could be because everyone has their cameras trained on the main event about to happen which is, admittedly, much more spectacular.
Second contact occurs when the moon completely covers the sun.
The edge of the moon is not perfectly round. There are mountains and valleys that make the edge less than smooth.