Once a year, the Manhattan grid comes into astronomical alignment with the sun. In practical terms, this means that if you are sitting on the East Side looking west you can see the Sun shining down a canyon-like street. According to wikipedia, the term is derived from Stonehenge, at which the sun aligns with the stones on the solstices.

Tomorrow is that day and all of us living in Manhattan will be treated to a trully amazing sunset. One more reason to love this city.