longer in summer, just as the interval of dawn varies with the night and is therefore longer in winter.
Anyone who claims that the interval before ‘Ishā’ equals the interval of dawn in both winter and summer has made an error contradicted by sensory observation, as everyone agrees. His error arises because light depends on vapours. In winter, vapours are more abundant at night, so light appears earlier, whereas in summer there are fewer vapours at night. In summer, vapours make the atmosphere hazy during the day, whereas it is clear in winter, because the sun has dispersed the vapour and the rain has settled the dust.
Furthermore, both lights depend on the sun: one precedes it and the other follows it. They must therefore vary with the sun. In winter, the sun remains absent longer, so the light associated with it lasts longer.
As for equating these two intervals, claiming that dawn lasts longer in summer and the interval before ‘Ishā’ lasts longer in winter, making dawn correspond to the day—lengthening in summer and shortening in winter—and making twilight correspond to the night—shortening in summer and lengthening in winter—this turns sensory observation, reason, and revealed law on their heads. The appearance of darkness is not delayed beyond sunset. And Allah knows best.