(This is an artificially symmetrized photograph i.e. a mirror image of itself and should not be mistaken for a real image.)
<p>Because of the absence of gravity, fuels burning in <a href="//commons.wikimedia.org/wiki/Space" class="mw-redirect" title="Space">space</a> behave very differently from how they do on <a href="//commons.wikimedia.org/wiki/Earth" title="Earth">Earth</a>. In this image, a 3-millimeter diameter droplet of <a href="//commons.wikimedia.org/w/index.php?title=Heptane&amp;action=edit&amp;redlink=1" class="new" title="Heptane (page does not exist)">heptane</a> fuel burns in microgravity, producing soot. When a bright, uniform back-light is placed behind the droplet and <a href="//commons.wikimedia.org/wiki/Flame" title="Flame">flame</a> and recorded by a video camera, the soot appears as a dark <a href="//commons.wikimedia.org/wiki/Cloud" title="Cloud">cloud</a>. Image processing techniques can then quantify the soot concentration at each point in the image. On the <a href="//commons.wikimedia.org/wiki/International_Space_Station" title="International Space Station">International Space Station</a>, the NASA Flame Extinguishment Experiment (FLEX) examines the combustion of such liquid fuel droplets.
</p>
This colorized gray-scale image is an artificially symmetrized composite of the individual video frames of the back-lit fuel droplet. The bright <a href="//commons.wikimedia.org/wiki/Yellow" class="mw-redirect" title="Yellow">yellow</a> structure in the middle is the path of the droplet, which becomes smaller as it burns. Initial soot structures (in <a href="//commons.wikimedia.org/wiki/Green" title="Green">green</a>) tend to form near the liquid fuel. These come together into larger and larger particles which ultimately spiral out of the flame zone in long, twisting streamers.
NASA
<a rel="nofollow" class="external text" href="http://www.nasa.gov/multimedia/imagegallery/image_feature_1956.html">NASA Image of the Day</a>