Don't just take the word of scientists who tell you that light bends towards dense air. You can actually check it for yourself! While this is a fun science experiment, it's also of relevance to believers in the "Flat Earth" conspiracy theory. Observations of distant object are often affected by refraction, so a discussion of this will go better if you (and they) have some practical experience of how refraction in air works. Transcript: Science tells us that light bends towards air that is more dense. When looking towards the horizon this generally bends the light down because air less dense as you get higher. If there's large changes in temperature then this can change things. Low cold air bends the light down more, low warm air will bend the light upwards, sometimes creating mirages. But how can you demonstrate this for yourself? It's actually easy to do with common items. Take a laser pointer and bounce it off a mirror at the other end of the longest room you have (about 30 feet here). This makes the position of the dot very sensitive to small bends at the start of the laser beam. Then take a flame and put it next to the laser. Heating up the air makes it expand, which makes it less dense. So the laser bends away from it and towards the cooler air further from the flame. For cold air take a large ice pack, or even a tray of ice cubes, and position it under the beam. This cools the air directly above the ice, making the more dense, and so bends the beam downwards towards the cold dense air. What about changes in pressure? I took a plywood board and slammed it down onto the beam. This compresses the air ahead of the board, making it more dense, so you'd expect the first movement of the beam to be upwards. This is hard to see in this shot, but it is measurable. If we repeat it in slow motion this initial movement becomes more obvious, up towards the wave of higher pressure, more dense air. ... https://www.youtube.com/watch?v=uh3BmK7NzDc

Steel wool does not need a particularly hot flame to ignite and form microspheres. Here I ignite some steel wool with a piece of burning wood. ... https://www.youtube.com/watch?v=Y12ri1fNDEQ