image credit: NASA; larger image
Not Just Another Old Flame
The photo shows two flames, one on Earth and one in space.
On Earth, the heat produced by the candle expands the nearby gas, and it makes the gas more buoyant, so it rises and produces the tall flame. Up in the Space Shuttle, it's quite different, since the Shuttle, the air inside, and the candle are in free fall; everything falls around Earth together, so there is no up or down created by gravity. In space, the flame spreads out equally in all directions, distributing the heat into a far larger volume than on Earth, and producing the cool blue flame.
To learn more, visit Not Just Another Old Flame.
Floating Flame Balls
In low gravity, fire behaves differently from our expectations, like in the image above. Read about the discovery of flame balls at Floating Flame Balls and more about the ongoing research in this Discover Magazine article.