Flames of all sorts flicker when they receive either too much fuel or too much air. A candle flame flickers while burning when carbon particles from the wick escape before they get a chance to combust! (I'll bet you weren't thinking about carbon molecules during that recent candlelit date night.)
2. How does a candle flame get its upside-down teardrop shape?
Your favorite candle works by melting the wax in the center, which is then "sucked up" the wick as the hot air rises. Next, the wax is vaporized by the flame, turning into a hot (and fragrant!) gas that diffuses into the air. As heat rises and cool air replaces it, the flame is drawn into that classic inverse teardrop shape. (Bonus fact: The hottest part of a candle flame–the blue section at the base of the wick–can reach up to 2500 degrees Fahrenheit.)
3. Can a candle burn in space?
When astronauts lit candles on the International Space Station, they found that the resulting flames were perfectly spherical in shape, not that typical teardrop. This is because there's no gravity in space to cause cold air to sink and hot air to rise. (You won't regret looking up the photos if you're a science and/or candles nerd like me. Or if you've already burned through half of Netflix during self-isolation and have nothing left to do but wash your hands.)
4. Is the first burn really that important?