This long-exposure photograph taken in a forest in Okoyama,
Japan by photographer Tsuneaki Hiramatu
showcases one of the best-known and beloved examples of bioluminescence -- fireflies.
The glow is caused by a chemical reaction inside the insect's abdomen. An
enzyme called luciferase and molecular oxygen oxidise a light emitting compound
called luciferin, with adenosine triphosphate as an energy source, to create a
glow in the 510-670-nanometer wavelength. This produces a yellow, green, or
pale red glow.
This makes them quite lovely to look at, but the mechanisms
behind the firefly glow have some uses in science as well.
often used as bioindicators for gene expression studies, and can also be used in medicine to detect blood clots, proteins and even cancerous cells. Some
researchers are even experimenting with firefly luminescence to create electricity-free lighting.
Lisa & Jeffrey Smith/Light Exhibit
Cow and rainbow
Most people know what causes a rainbow: Light enters miniscule
droplets of water in the air. At the point of entry, the light is bent as it
enters 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 the
way out. Different colours are produced when the refraction occurs at slightly
different angles, which results in the rainbow. Because, however, of the way
light enters, bounces off and then exits the droplets, you'll only ever see a
rainbow when the light source is behind you. Skeptical? Take a look at some photos.
Dr Paula Fontaine/Light Exhibit
X-ray light bulbs
We've all seen medical X-rays, and know -- at least on a
very basic level -- how they work. The subject is placed between an X-ray
detector and an X-ray source. Pulses of X-ray -- a form of electromagnetic radiation able to pass through materials that absorb visible light -- are
then sent through the subject. Because materials with higher atomic mass -- in
the case of bone, calcium -- absorb X-rays better, the image taken by the
detector clearly shows the subject's bones. In this series, artist Dr Paula Fontaine has X-rayed
light bulbs, adding the colour afterward for artistic effect.
ESO/Babak Tafreshi/Light Exhibit
Astronomical observatories need to be in isolated locations,
in order to minimise light pollution. Often, these giant telescopes are trying
to capture images of objects hundreds or thousands of light-years away; so you
might think shining a laser into the sky counter-intuitive. On the contrary,
the laser -- a tightly focused beam of light -- allows astronomers to
compensate for any blurring caused by the Earth's atmosphere.
The beam is shot into the sky, where it excited a layer of
sodium atoms at an altitude of 90 kilometres, just below the Karman line. This
creates an artificial star within the Earth's atmosphere; this star is then
used as a reference point for an array of computer-controlled deformable
mirrors, which are adjusted hundreds of times per second to correct atmospheric
Salt Lake City from space
From aboard the ISS, the Earth at night glitters and glows
with the light of human habitation. This is, technically, light pollution; but
it'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 crawling
There she is -- our magnificent sun -- our planet's main
source of light and warmth, without which life would
simply be unable to exist. It gives off much more than visible light, and some
of that data is now available to us, thanks to NASA's Solar Dynamics Observatory, a telescope
that can image the sun in a variety of different wavelengths. This
image shows the sun in the extreme ultraviolet wavelength, with the reds
showing cooler temperatures -- about 60,000 degrees Kelvin (107,540 F) -- and blues
and greens showing temperatures of 1 million degrees Kelvin (1,799,540 F) or
Marek Mis/Light Exhibit
This rather stunning looking collection of colours... well,
it's probably less interesting than it looks. It's a photomicrograph -- a
photograph taken using a microscope, by photographer Marek Mis -- of a decongestant
drug called Acatar and a common food additive called sodium citrate, taken in
polarised light. Normally, light vibrations can travel in all directions. Polarisation
is the technique whereby some directions are blocked, restricting the
vibrations to a single plane. This can be used in photomicrography to highlight
Frank Fox/Light Exhibit
Volvox under the microscope
This rather geometric looking structure is actually a type
of green algae called volvox -- which forms spherical colonies made up of
perfectly placed flagellate cells in the surface of a hollow sphere. These
cells coordinate their swimming, as indicated by their eyespots and posterior
and anterior positions. When viewed under an optical microscope -- also known
as a "light microscope", a type of microscope that uses light and
lenses to magnify tiny samples -- the details of this matrix spring into clarity,
as seen in this image by Frank Fox. The
green sphere on the right is a "daughter" colony, growing on the
surface of an older colony. Eventually the parent colony will disintegrate,
giving "birth" to the younger colony.
Earth, as time goes by
Timelapse photos are a great way to capture aggregate
information. They involve leaving the lens of a camera open for a
longer-than-usual amount of time; this captures not a snapshot of a single
moment, 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.
X-ray: NASA/CXC/UMass/D. Wang et al.; Optical: NASA/ESA/STScI/D.Wang et al.; IR: NASA/JPL-Caltech/SSC/S.Stolovy
The heart of the Milky Way
At the heart of the Milky Way galaxy -- astronomers believe
-- is probably a supermassive black hole. It's hard to tell, not just because
of the clouds of dust and matter that surround our galaxy's core, but because
black holes absorb all light -- meaning we can only really find out information
about them by observing their effect on the space and objects around them.
This image of the Milky Way's heart, released in 2009, is a composite comprising
data from NASA's three great observatories, Chandra, Hubble and Spitzer.
Chandra contributed X-ray data, visible in blue and violet, indicating gas
heated to millions of degrees by stellar explosions and outflows from the black
hole. Hubble contributed near-infrared data, visible in yellow, indicating
high-energy regions where new stars are being born. Spitzer contributed
infrared, visible in red, indicating glowing dust clouds created by solar
radiation and wind.
The very bright blob on the right side of the image? That's
the centre of the Milky Way galaxy, visible through the dust thanks to imaging
technologies that are able to see beyond visible light.