Meanwhile, hypotheses explaining the evolution of the Sun originated in the nineteenth century, especially as scientists began to understand how stars in general functioned. In contrast, hypotheses attempting to explain the origin of the Moon have been circulating for centuries, although all of the widely accepted hypotheses were proven false by the Apollo missions in the mid-twentieth century. Following Apollo, in 1984, the giant impact hypothesis was composed, replacing the already-disproven binary accretion model as the most common explanation for the formation of the Moon.