The breathtaking art and science of light (pictures)

This long-exposure photograph taken in a forest in Okoyama,Japan by photographer Tsuneaki Hiramatushowcases one of the best-known and beloved examples of bioluminescence -- fireflies.The glow is caused by a chemical reaction inside the insect's abdomen. Anenzyme called luciferase and molecular oxygen oxidise a light emitting compoundcalled luciferin, with adenosine triphosphate as an energy source, to create aglow in the 510-670-nanometer wavelength. This produces a yellow, green, orpale red glow.

This makes them quite lovely to look at, but the mechanismsbehind the firefly glow have some uses in science as well.

Luciferases areoften used as bioindicators for gene expression studies, and can also be used in medicine to detect blood clots, proteins and even cancerous cells. Someresearchers are even experimenting with firefly luminescence to create electricity-free lighting.

Most people know what causes a rainbow: Light enters minisculedroplets of water in the air. At the point of entry, the light is bent as itenters a thicker medium, where then light moves more slowly (called refraction). Then it is reflected off the back of the water droplet and bent again on theway out. Different colours are produced when the refraction occurs at slightlydifferent angles, which results in the rainbow. Because, however, of the waylight enters, bounces off and then exits the droplets, you'll only ever see arainbow when the light source is behind you. Skeptical? Take a look at some photos.

We've all seen medical X-rays, and know -- at least on avery basic level -- how they work. The subject is placed between an X-raydetector and an X-ray source. Pulses of X-ray -- a form of electromagnetic radiation able to pass through materials that absorb visible light -- arethen sent through the subject. Because materials with higher atomic mass -- inthe case of bone, calcium -- absorb X-rays better, the image taken by thedetector clearly shows the subject's bones. In this series, artist Dr Paula Fontaine has X-rayedlight bulbs, adding the colour afterward for artistic effect.

Astronomical observatories need to be in isolated locations,in order to minimise light pollution. Often, these giant telescopes are tryingto capture images of objects hundreds or thousands of light-years away; so youmight think shining a laser into the sky counter-intuitive. On the contrary,the laser -- a tightly focused beam of light -- allows astronomers tocompensate for any blurring caused by the Earth's atmosphere.

The beam is shot into the sky, where it excited a layer ofsodium atoms at an altitude of 90 kilometres, just below the Karman line. Thiscreates an artificial star within the Earth's atmosphere; this star is thenused as a reference point for an array of computer-controlled deformablemirrors, which are adjusted hundreds of times per second to correct atmosphericdistortion.

From aboard the ISS, the Earth at night glitters and glowswith the light of human habitation. This is, technically, light pollution; butit's spectacularly beautiful. All the lights of a city -- homes, businesses,streetlights, the cars on the road; incandescent bulbs, which burn a filament, fluorescent,which burn a gas, LED -- all combine to indicate a planet alive and crawlingwith life.

There she is -- our magnificent sun -- our planet's mainsource of light and warmth, without which life wouldsimply be unable to exist. It gives off much more than visible light, and someof that data is now available to us, thanks to NASA's Solar Dynamics Observatory, a telescopethat can image the sun in a variety of different wavelengths. Thisimage shows the sun in the extreme ultraviolet wavelength, with the redsshowing cooler temperatures -- about 60,000 degrees Kelvin (107,540 F) -- and bluesand greens showing temperatures of 1 million degrees Kelvin (1,799,540 F) orgreater.

This rather stunning looking collection of colours... well,it's probably less interesting than it looks. It's a photomicrograph -- aphotograph taken using a microscope, by photographer Marek Mis -- of a decongestantdrug called Acatar and a common food additive called sodium citrate, taken inpolarised light. Normally, light vibrations can travel in all directions. Polarisationis the technique whereby some directions are blocked, restricting thevibrations to a single plane. This can be used in photomicrography to highlightcertain details.

This rather geometric looking structure is actually a typeof green algae called volvox -- which forms spherical colonies made up ofperfectly placed flagellate cells in the surface of a hollow sphere. Thesecells coordinate their swimming, as indicated by their eyespots and posteriorand anterior positions. When viewed under an optical microscope -- also knownas a "light microscope", a type of microscope that uses light andlenses to magnify tiny samples -- the details of this matrix spring into clarity,as seen in this image by Frank Fox. Thegreen sphere on the right is a "daughter" colony, growing on thesurface of an older colony. Eventually the parent colony will disintegrate,giving "birth" to the younger colony.

Timelapse photos are a great way to capture aggregateinformation. They involve leaving the lens of a camera open for alonger-than-usual amount of time; this captures not a snapshot of a singlemoment, but the paths light travels as it moves. This timelapse of the Earth,taken from the ISS by NASA astronaut Done Petit, shows several types of light:star trails in the sky; lightning (the bright flashes); aurora; and, of course,the electric light created by human cities.