- The shape and behavior of a candle flame differ dramatically between Earth and space due to the influence of gravity on air movement and combustion dynamics.
- On Earth, a candle flame takes on the familiar teardrop shape. This is primarily the result of gravity-driven convection. When the candle burns, the hot gases produced rise rapidly because they are less dense than the surrounding cooler air. As these hot gases move upward, cooler air rich in oxygen is drawn in at the base of the flame to sustain the combustion. This constant upward flow gives the flame its elongated, pointed form. The yellow color of the flame is due to incomplete combustion and the presence of incandescent soot particles, which glow as they are heated.
- In space, however, the absence of gravity eliminates convection currents. Without a natural “up” or “down,” the hot gases do not rise, and the supply of oxygen must reach the flame through slow molecular diffusion rather than rapid airflow. As a result, the flame becomes spherical and symmetrical, surrounding the wick evenly on all sides. This shape is more stable and does not flicker like it does on Earth. Interestingly, the flame in microgravity burns with a bluish color, indicating more complete combustion and a lower presence of soot.