X-rays and UV radiation that is released by solar flares can affect Earth's ionosphere. Because of this, radio communications, radars and other devices may be disrupted for a short time. Richard Christopher Carrington was the first person to observe a solar flare in 1859. Carrington had spotted brightening's of small areas within a sunspot group. Stellar flares have also been observed on several of other stars. Solar flares can be "active" from several flares a day or "quiet" from several flares every week. Solar flares occurs during the 11-year cycle (the solar cycle). There are less "large flares" than smaller ones.