It may be possible to measure the differential of stars that regularly emit flares of radio emission. Using 7 years of observations of the M9 ultracool dwarf TVLM 513-46546, astronomers were able to measure subtle changes in the arrival times of the radio waves. These measurements demonstrate that the radio waves can arrive 1–2 seconds sooner or later in a systematic fashion over a number of years. On the Sun, active regions are common sources of radio flares. The researchers concluded that this effect was best explained by active regions emerging and disappearing at different latitudes, such as occurs during the solar sunspot cycle.