Boston Sunset and Glacial Landforms

August 25, 2010

BostonSunset1

Photographer: Declan De Paor
Summary Author:Declan De Paor; Jim Foster

The photo above photo showing a burnt orange sunset over Boston Harbor was taken one week ago, just a minute before sunset. When the Sun is near the horizon, the longer path length the Sun's rays must take to reach us results in the shorter wavelength (blue and violet colors) being scattered from our view. Only the longer wavelengths (yellows, oranges and reds) remain to paint the western sky. It's just not the act of rising or setting that's responsible for color. There must be something to reflect or scatter the waning sunlight such as clouds, dust or salt particles.

The silhouetted horizon featured here includes downtown Boston skyscrapers to the right, Telegraph Hill (with historic tower) at center, and Hull Hill to the left. These hills are drumlins formed during the last glaciation, at a time when the Earth's axis was slightly different in orientation and the Sun's rays were consequently less effective in warming this latitude. This shot was snapped from the northern end of Nantasket Tombolo; a sand spit that joined these drumlins together in the last few millennia. Note the crepuscular rays stretching across the sky. They may result from distant clouds or from gaps in the Appalachian Mountains, below the horizon (in western Massachusetts), where the Sun is shining through.

Photo details: Camera: Panasonic Lumix DMC-ZS7; moderately zoomed; automatic "sunset scene" setting; azimuth of Sun was 288° at 7:40 p.m. local time on August 18, 2010.