Quetelet Scattering and Ponies on Assateague Island

May 08, 2018


Photographer: John A. Adam
Summary Author: John A. Adam

I noticed these iridescent colors on the surface of a pond while on a walk on the island of Assateague, Virginia. They're caused by interference between sunlight reflected from the pond surface and light scattered by pollen or dust particles floating just above the surface (and subsequently reflected by it). A fine example of this phenomenon can be found here. It's called Quetelet scattering, named for the polymath Lambert Adolphe Jacques Quetelet (1796–1874) a Belgian astronomer, mathematician, statistician and sociologist. He founded (1828) and directed the Royal Observatory in Brussels and was influential in introducing statistical methods to the social sciences. He also developed the body mass index scale, originally called the Quetelet Index. See Related Links for an alternative explanation to the colors featured above.

Assateague Island is a 37-mile (60 km) long barrier island located off the eastern coast of the Delmarva Peninsula facing the Atlantic Ocean. The northern two-thirds of the island is in Maryland while the southern third is in Virginia. It's known in particular for the ponies that inhabit it, and once a year in late July, some are rounded up and encouraged to swim across to Chincoteague, Virginia to be sold at auction to benefit the Chincoteague Volunteer Fire Company.

Photo Details: Top - Camera: OLYMPUS DIGITAL CAMERA SP-100EE; Exposure Time: 0.0025s (1/400); Aperture: ƒ/5.0; ISO equivalent: 125; Focal Length (35mm): 88. Bottom - Camera: Motorola Moto G (5) Plus; Exposure Time: 0.0011s (1/950); Aperture: ƒ/1.7; ISO equivalent: 64; Focal Length: 4.3mm.