This tangle of closed squiggly loops is actually the glitter and glints of moonlight shining on the ocean; the twisted jumble of moonlight emerged naturally in a four-second, time-lapse image. The long exposure was able to produce this effect because it captured the motion of waves across the surface of the ocean, which traced out circular patterns of reflected moonlight.

As the waves pass across the surface, single glints appear at the leading edge of the waves. The reflections briefly brighten and then split into two separate glints that travel around the surface of the wave before rejoining, brightening, and then vanishing altogether as the wave-front passes.

Closed loops are actually very common. They can be seen by night and day in any rippled water surface that reflects point-like light sources, such as ponds, pools, and even a cup of coffee.

Image credit: David K. Lynch/Applied Optics

Paper: Glitter and Glints on Water, Applied Optics, Vol. 50, Issue 28, pp. F39-F49 (2011)

Brief Caption: A four-second color exposure of moon glitter on the ocean showing a plethora of closed trajectories of the glints.

Sun glints are remarkably bright, saturating and easily overpowering the unshielded eye, film, and electronic detectors. The Sun's rays are so bright that Earth's atmosphere does little to absorb or scatter the light. This enables the familiar glitter of sunlight on water to be seen in striking brilliance from space, as revealed in this image courtesy of NASA. Glitter is, in fact, the brightest incoherent light coming from the Earth.

Recently, other researchers have speculated that the same bright scattering of light from distant stars could be used to help detect extrasolar planets. The next generation of extremely large, segmented mirror telescopes on Earth – with their unprecedented apertures and sensitivity -- may be able to search nearby star systems for this tell-tale sign of other planets. If detected, this light would suggest that there are other water worlds in the universe. The light may even carry the spectrographic signature of the planet's atmosphere, revealing even more details about the possibility of life in the cosmos.

Image credit: Photo courtesy of NASA

Paper: Glitter and Glints on Water, Applied Optics, Vol. 50, Issue 28, pp. F39-F49 (2011)

Brief Caption: The glitter of sunlight on Earth's oceans as seen from space. The optical signature of glitter from oceans on extrasolar planets might be detectable from Earth, thereby providing a way to search for such planets.

Thin clouds in the sky can diffract light from the Sun or Moon, spreading it out into many-colored rings that closely encircle the celestial bodies. The rings, known as a corona, were conventionally believed to be caused by tiny liquid water droplets, since the ice crystals generally found in clouds were too large to separate the colors of light on a scale discernable to the human eye.

In this photo, a green laser beam shone from within a building at Montana State University is used to probe the composition and height of the high-atmospheric wave cloud that produced the observed lunar corona. Both the manner in which the cloud altered the polarizing beams and the height of the cloud (almost 10 km above the surface of the Earth, where temperatures are around -70 Celsius) indicate the corona is in fact caused by unusually tiny ice crystals. By measuring the angular properties of the corona's rings, researchers calculated that the diameter of the crystals were around 15 microns, less than half the diameter of an average human hair.

Image credit: Joseph A. Shaw/Applied Optics

Paper: Icy wave-cloud lunar corona and cirrus iridescence, Applied Optics, Vol.50, Issue 28, pp. F6-F11 (2011)

Brief caption: A green laser beam is used to probe a thin wave cloud to determine that the colored rings around the Moon (called a lunar corona) are caused by diffraction from unusually tiny ice crystals rather than the conventionally believed liquid water droplets.

These silver-blue clouds, known as noctilucent clouds, are the highest clouds in the atmosphere, occurring 80-85 kilometers (50-53 miles) above Earth's surface and require very specific atmospheric conditions to form. They are seen only during the short summer nights between late May and the middle of August, and then only in mid- and high-latitude regions around the globe.

These clouds are so tenuous that they are discernible only during twilight hours, and appear almost transparent, with a smattering of stars peeking through. Their distinctive bluish hues come from tiny ice crystals that form them. The ice crystals scatter the final rays of the Sun that still illuminate the upper atmosphere. The scattered sunlight obliquely passes the ozone layer, which filters out the reds, revealing these transient and evocative formations.

Image credit: Audrius Dubietis/Applied Optics

Paper: Noctilucent clouds: modern ground-based photographic observations by a digital camera network, Applied Optics, Vol. 50, Issue 28, pp. F72-F79 (2011)

Brief caption: Tenuous noctilucent clouds, which form high above the Earth and only under very specific atmospheric conditions, as seen at twilight from Salakas, Lithuania.

Road mirages, like the one in this photograph, occur when there is a large difference in temperature between the air immediately above a stretch of hot asphalt and the cooler air a few feet above the road. Small-angle light rays that would normally hit the ground are instead reflected up, so that observers see a mirror reflection of objects near the road instead of seeing the road itself.

In this image, a street sign is reflected in such a mirage. But parts of the image are not inverted the way they should be: notice that the arrow in the reflection is pointing in the same direction (right and downward) as the arrow on the sign itself (blue circular sign, center of image). Scientists have determined that this partial "non-inversion" of objects in a mirage is likely caused by slight undulations in the surface of the road. The undulations form concave and convex mirage "mirrors" that distort the reflection like a funhouse mirror, causing most of the image to be reflected normally, but parts of it to appear in the same orientation as the object being reflected.

Image credit: Siebren van der Werf/Applied Optics

Paper: Noninverted images in inferior mirages, Applied Optics, Vol. 50, Issue 28, pp. F12-F15 (2011)

Brief caption: What's Wrong with This Picture? Slight undulations in the road can turn a mirage into a "funhouse mirror" where certain parts of a reflection are not inverted, like the downward-facing arrow in this street sign.

When conditions are just right, a "supersun," like the one in this image, appears in the sky above the setting Sun. This feature is created when sunlight bounces off the underside of horizontally oriented ice crystals suspended in the air. The phenomenon is usually only visible to people on airplanes or high in the mountains, in situations where the Sun itself is below the true horizon (as it would appear to a person standing at ground level) but not yet below the horizon of the airborne observer.

Notice the supersun's elongated appearance in the photograph. This vertical stretching is due to the curvature of the Earth. Collectively, the faces of all the tiny airborne ice crystals act as a giant concave mirror. At lower altitudes, where there is a smaller difference between the observer's horizon and the true horizon, small irregularities in the orientation of the ice crystals cause the reflected light to stretch into a pillar that rises into the sky. At higher altitudes, the curvature of the Earth causes the supersun to look more compact and distinct, as it does here.

An observer standing at ground level will never see a supersun, since the light bouncing off the crystals will always be blocked by the surface of the Earth.

Image credit: Gunther Können/Applied Optics

Paper: Reflection halo twins: subsun and supersun, Applied Optics, Vol. 50, Issue 28, pp. F80-F88 (2011)

Brief caption: A supersun, as seen from an aircraft 39,000 feet (12 km) above Norway. Ice crystals suspended in the air can reflect light from the setting Sun, creating a special kind of mirror image where a second "sun" appears above the real one.

Sunlight paints a dappled pattern of bright and dark spots at the bottom of a pool, as instantaneously captured by two cameras spaced a set distance apart. By recording the way the segmented light pattern flickers and shifts over time in two different video sequences, a computer system can differentiate between pixels that correspond to the same point in space (marked by an X) and pixels that correspond to different points in space (marked with an X in photo a and a dot in photo b). After matching corresponding pixels, the system can then triangulate the distance to each point in the image, creating 3-D vision with accurate depth perception.

Image credit: Yohay Swirski, Yoav Y. Schechner, Ben Herzberg and Shahriar Negahdaripour/Applied Optics.

Paper: CauStereo: Range from light in nature, Applied Optics Vol. 50, Issue 28, pp. F89-F101 (2011)

Brief caption: Sunlight paints a dappled pattern of bright and dark spots at the bottom of a pool, as instantaneously captured by two cameras spaced a set distance apart. By matching the way the segmented light pattern flickers and shifts over time in two different video sequences, a computer system can create underwater 3-D vision.