Want to see convection cells for yourself? Get a glass pan and fill it up with water. Add some food coloring to the water. Next put a candle underneath the pan, right in the middle. You should see the food-coloring move around in a circle, a miniature convection cell.
The same way a person may cast a shadow over another person when they stand under the sun, planets or celestial bodies that have aligned themselves cast shadows over one another as well.