Infrared images reveal the 'cold coats' that help keep emperor penguins warm The outer surface of an emperor penguin is colder than the air around it On average the surface is four to six degrees Celsius colder than the air The only exposed parts that are warmer are the eyes, beak and feet Scientists believe extreme radiative cooling is the explanation It may be minus 40 degrees Celsius outside but the outer surface of an emperor penguin is even colder than the air around it, scientists have discovered. Pictures captured with an infrared thermal imager show that the penguins" outer surfaces are on average between four and six degrees Celsius cooler than the surrounding air. Researchers at the University of Glasgow studied images of 40 penguins and discovered that the part of a penguin that is covered by thick plumage, dubbed a 'cold coat', is colder than the surrounding air. Pictures captured with an infrared thermal imager show that the penguins' outer surfaces are cooler than the surrounding air The only exposed parts of the animals that are warmer than the air are the unfeathered eyes, beaks and feet The only exposed parts of the animals that are warmer than the air are the unfeathered eyes, beaks and feet. The scientists also discovered that the only part of the birds" surface that is warmer than freezing is the eye. Dr Dominic McCafferty, a biophysical ecologist at the University of Glasgow, told the BBC: "Most of the body that is covered by thick plumage was found to be, on average, 4 to 6 degrees Celsius colder than surrounding air temperature. At first, we were very surprised by this discovery. The scientists believe that the observations of the breeding colony in Terre Adelie, Antarctica, suggest that extreme radiative cooling draws heat from a penguin's surface. The only part of the birds' surface that is warmer than freezing is the eye Dr McCafferty next hopes to use thermal imaging to study how huddling together helps penguins save energy Radiative cooling occurs when heat is released into space from the penguins" body surface making it cooler than might otherwise be expected. The report, which was published in Biology Letters, also claims that because of the penguins" layers of insulating fat and feathers they can maintain a body temperature of 39 degrees Celsius even when the air temperature is minus 40. Dr McCafferty next hopes to use thermal imaging to study how huddling together helps penguins save energy. Radiative cooling is the process by which a body loses heat through thermal radiation. It is commonly experienced on cloudless nights when heat is released into the atmosphere from the surface of the Earth, or the outer surface of an animal. It is the sum of the three sources of radiation: outgoing radiation from objects versus incoming sky and cloud radiation. Maximum radiative cooling occurs when the sky is clear, it is dry and there is little wind.