Birkat hachama, the blessing of the sun, is a custom that Jews can perform once every 28 years. It is believed that every 28 years the sun returns to the place – relative to earth – where it was created. Why once every 28 years? It has to do with the day of the week, the season and the time of day… It gets complicated. But a friend of mine sent me this video that explains it really well. It is around 45 minutes long but very worthwhile.