When cooking on a gas stove, the colour at the centre of the flame is blue, which seems a little strange considering the association of blue with cold and red with hot.
In fact, if you blink, you might miss seeing that sometimes the tips of the flame can be red or orange. It’s the same as how a flame on a match head will appear orange, because it has a cooler temperature than the base of the flame on a gas-fed stove top.
The principle behind this is called colour temperature. The range of flames in particular run from red being of the lowest heat, and blue burning hottest. This is also true of stars, as they are giant balls of flaming gasses.
Applications Aside from Burning Yourself
Outside of flames, colour temperature isn’t a very easy idea to juggle. Colour temperature is an important concept to understand in both moving and still photography, and many products exist to measure it. I once heard a portrait photographer say, “The right side of her face is too hot,” and that’s really not a judgement on her at all. What it means is that the light source they’re using to emulate natural light is casting too much light on that specific side of her face, and is raising the colour temperature, which will over-expose the film in camera. Film is particularly fickle, and is often designed with specific light exposure in mind, like daylight or indoors. Colour temperature can be used in photography artistically, of course, as twilight and sunrise have less light and less colour temperature than mid-day, when colour temperature is at its fullest. Unfortunately, studio lighting and daylight are about two-thousand degrees apart from each other, and what that’s based on is called black body radiation.
Objects in Space
A black body is something that absorbs electromagnetic radiation, which is found throughout the universe. The radiation is not permitted to pass through or be reflected by a black body, and instead, its thermal emissions can be read as a scale of perfect colour temperature. What this means for you and I, the non-rocket scientists, is that we can tell by comparison which flames and stars in the night sky are hotter or colder by appearance.
Gas Giants
While some of the largest stars found can have surface temperatures of 50,000 degrees Kelvin, our star, The Sun, only has a few thousand degrees Kelvin in temperature. To give an idea of what temperature measured in Kelvin is, let’s view by comparison.
While the freezing point for ice in Celsius and Fahrenheit respectively are 0 and 32, the freezing point in Kelvin is 273.15, and for water to boil, about 100 Celsius and 212 Fahrenheit, while Kelvin reads 373.
As far as colour temperature goes, the stars are just like the stove top flame in temperature. Red stars are the lowest in temperature while blue is the hottest, and white falls in the middle, but do know that your stove top is not as hot as the sun. While the colour temperatures might be different, the actual temperature is on a much different scale, so put away those wax wings. It’s a lot hotter out there than it looks.
