The evening display of tethered, glowing hot-air balloons is commonly called a night glow.
During a night glow, balloons remain on the ground or tethered in place after dark. Pilots ignite their burners in coordinated sequences, lighting the colorful envelopes from within. Because the balloons are not freely flying, the display can be staged safely for spectators while still showing the shapes and designs of the envelopes.
Night glows are a major attraction at balloon festivals, including the Albuquerque International Balloon Fiesta in New Mexico. They are usually scheduled after sunset, when the contrast between the dark sky and the burner flames makes the envelopes especially vivid.
A night glow is different from a mass ascension. In a mass ascension, balloons take off and drift away under the control of their pilots. In a night glow, the balloons typically stay tethered, and the visual effect comes from timed bursts of burner flame rather than flight.