• Question: Can a candle burn without gravity?

    Asked by jammydodger72x to Alexander, Josh, Serena, Simone, Stuart on 17 Jun 2013.
    • Photo: Simone Sturniolo

      Simone Sturniolo answered on 17 Jun 2013:

      Given some oxygen, I think it would. To be sure one would have to make an experiment, but I guess this would need a very controlled environment – astronauts tend to be very touchy about lighting fires when they have huge quantities of potentially explosive fuel aboard, an oxygen enriched pressurized atmosphere, and nothing but a thin aluminium alloy layer separating them from an untimely and rather painful death. Gruesome jokes aside, I think a candle would burn in absence of gravity, but how long is a different matter. On Earth, candles burn upwards because gravity makes the hot hair of the flame rise (or rather, it makes the colder air go down, which in turn makes the hot air rise). This wouldn’t happen without gravity, and the candle’s flame would have a blob-like shape. I think it would be beautiful and weird to see, but this would also mean that it wouldn’t burn in the right direction, and it could risk getting “suffocated” by the candle’s wax. But maybe it would work out somehow. It would be messy though: can you imagine having hot molten wax droplets floating all around the spaceship? Yeah, I don’t think they’re going to switch from electric lights to candles any soon on the ISS.

    • Photo: Stuart Archer

      Stuart Archer answered on 17 Jun 2013:

      Candles do indeed burn in space, and as Simone says they do burn in sphere shape. There’s a great video of them burning one on the Mir space station a few years back

      I’m sure you’ve come across the idea that hot air rises – this is because hot air is less dense than cold air and ‘floats’ on top of it, as the heavier air is kept close to the ground due to gravity. This is why a candle burns upwards – the hot air created when it burns rises upwards. This difference in density doesn’t exist in a space station because there is no gravity. As the candle burns, it heats the air around causing it to expand, and as there’s no gravity it will expand in all directions, creating the spherical shape you can see in the video.

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