Today, NASA's Image of the Day features a look at Manhattan (below around 135th Street). Along with the vivid photo, NASA also offers a lesson in the "heat island effect," which we'll keep in mind during this cloudy stretch:

On Manhattan itself, the main visual features are Central Park (with playing fields appearing as white dots) and two darker zones where the tallest buildings of Midtown and the Financial District cast long shadows even in this early afternoon view.

In such an urban setting, rivers and parks can reduce the heat island effect, the local zone of higher surface and air temperatures caused by the way concrete and tarmac (asphalt) absorb, store, and release heat. Rivers provide pathways for wind, and the cooling effect of vegetated parks can be detected by space-based instruments that measure the temperature of the ground surface.

Tall buildings have a more complex effect. Shadowed zones in the “urban canyons” between tall buildings receive fewer hours of direct sunlight per day. But where that light can reach the canyon floors, energy is reflected back up at the walls of the buildings, where it is absorbed and later released as heat. This is especially the case at night, when urban canyons retain more heat than parts of the city with shorter buildings.

So that's why your Con Ed bill may be so high, Midtown residents!

With the "heat island effect" it's up to 5 degrees warmer during the day and 22 degrees warmer at night. A recent study also pointed out that electronic billboards and lights aren't helping things. Luckily, many area businesses help balance things out by opening up their doors and blasting the A.C. The system works!