Interestingly, candle flames take on a teardrop shape on Earth, but they appear spherical in outer space.
According to the National Candle Association (based in Washington D.C., USA), there are many chemical and physical theories behind the beauty and light of a candle flame. In fact, the scientific community has been “fascinated” by candles for over 100 years and continues to seek explanations for the phenomena associated with them.
In 1860, scientist Michael Faraday delivered a series of now-famous lectures on the chemistry of candles, demonstrating dozens of scientific principles through his careful observations of burning candles.
By the late 1990s, the National Aeronautics and Space Administration (NASA) elevated candle research to new heights by conducting experiments aboard the Space Shuttle to explore candle flames in a microgravity environment.
Scientists at various universities and research institutes worldwide continue to conduct experiments with candles to learn more about flame behavior, emissions, and the combustion process.
How Do Candles Burn?
All types of wax are essentially hydrocarbons, meaning they are primarily composed of hydrogen (H) and carbon (C) atoms.
When you light a candle, the heat from the flame melts the wax near the wick. This liquid wax is then drawn up the wick through capillary action.
The heat from the flame vaporizes the liquid wax (turning it into hot gas) and begins to break down the hydrocarbons into hydrogen and carbon molecules. These molecules rise to the flame, where they react with oxygen from the air to produce heat, light, water vapor (H2O), and carbon dioxide (CO2).
It takes a few minutes after lighting a candle for the burning process to stabilize. (Photo: pixels)
A sufficient amount of heat is generated to melt more wax, keeping the burning process ongoing.
It takes a few minutes after lighting a candle for the burning process to stabilize. Initially, the flame may flicker or smoke a bit, but once stabilized, the flame takes on a teardrop shape.
If it receives too little or too much airflow/fuel, the flame may revert to a flickering state or flare up, with unburned carbon particles (soot) escaping the flame before they can be completely combusted.
The smoke you sometimes see when the candle flickers is actually the result of unburned soot particles escaping from the flame due to incomplete combustion.
The Color of Candle Flames
If you closely observe a candle flame, you will notice it is divided into three basic color zones: the blue zone at the base of the flame, followed by a small orange/dark brown zone, and finally the large yellow zone that we typically associate with “candle flames.”
The blue zone, rich in oxygen, is where the hydrocarbon molecules vaporize and begin to break down into hydrogen and carbon atoms. Hydrogen is the first atom to separate here and reacts with oxygen to form water vapor. Some carbon atoms burn to produce carbon dioxide.
The candle flame is divided into 3 basic color zones. (Photo: Pinterest)
The orange/dark brown zone has relatively little oxygen. This is where various forms of carbon continue to break down, and small, solid carbon particles begin to form.
At the base of the yellow zone, the formation of carbon particles (soot) increases. As these particles rise, they continue to heat up until they ignite, emitting the spectrum of light we see.
Since the yellow part of the spectrum is predominant, when carbon burns, the human eye perceives the flame as slightly yellow.
In addition to the three basic color zones, the candle flame also has a fourth color zone. This is the pale blue rim at the outer edge of the candle flame, extending from the blue zone at the base of the flame upwards.
Why Does the Candle Flame Have a Teardrop Shape?
As the candle burns, the flame heats the surrounding air, causing it to rise. As this hot air moves upwards, cooler air and oxygen flow in at the base of the flame to replace it. This continuous cycle of air movement around the flame (convection current) creates the elongated or teardrop shape of the flame.
The candle flame appears spherical in outer space. (Photo: Pinterest)
Since the “up” and “down” movement of air currents here is influenced by gravity on Earth, scientists have wondered what a candle flame would look like in outer space, where gravity is minimal.
In the late 1990s, NASA scientists conducted several experiments aboard the Space Shuttle to observe how flames would behave in a microgravity environment. As we can see from NASA’s image above, the candle flame in a microgravity environment takes on a spherical shape, rather than the elongated shape seen on Earth. In other words, on Earth, flames rise vertically, but in space, they diffuse in all directions.
