Have you ever wondered how you steer a hot-air balloon? Steering a Balloon on today's Moment of Science.

Aircraft such as jets or propeller-driven planes have a way of pushing themselves forward. They also can bank left or right. But a hot air balloon doesn't have any way of pushing itself forward. It can only go up or down. So how can it move around? The wind! The wind moves horizontally and carries the balloon. But then how can you change direction?

You change direction by going up, or down, until you hit a different air current. At different heights, air currents will be blowing in different directions. By rising or dropping into the right currents, you can steer your balloon horizontally. Generally, winds tend to veer to the right as you gain altitude. Usually you can change direction by ninety degrees or more in the first couple of thousand feet.

This is why windy days are bad for ballooning. You want air that is generally calm and currents that are well-defined. Most often hot-air balloonists go up in the early morning or near dusk, when wind currents are gentle and predictable.