About 100,000 spicules are active on the Sun's surface at any given time. They rise from the lower chromosphere at about 20 km (12 miles) per second to a height of several thousand kilometres, and then within 10–15 minutes they disperse or collapse. Although they are invisible in white light, early observers could see them in the hydrogen alpha (Hα) emission line with a spectrograph and compared them to a “burning prairie.” Spicules are not connected with sunspots (sunspot) or plages and are also absent from the channels where solar prominences (solar prominence) appear.