Given the varying times for the Ishā’ prayer specified by different authorities in Cairo, and the fact that the time for Maghrib is not fixed, what is the correct time for the Ishā’ prayer to begin, and is it permissible to adopt any of these astronomical calculations?

Prayer times are known by cosmic signs. Maghrib time begins with the sunset and continues until the red twilight disappears, and with it, the time for Isha enters. Isha prayer is not valid before the red twilight disappears. Relying on astronomical calculations to determine prayer times has a specific ruling. The error rate for a calendar that equates between the schools of thought regarding the start of Isha is not accurate, as the majority agree that the beginning of Isha is when the twilight disappears, and they differed on the interpretation of twilight, whether it is the whiteness or the redness. What was mentioned about Imam An-Nawawi, that the time between sunset and the disappearance of the red twilight is half a sixth of the night, is neither general nor conclusive, so it cannot be relied upon. The Lawgiver made the disappearance of twilight a sign of the entry of Isha time. The verse is not a detailed text on prayer times, and the Sunnah (definition) clarified that. What was mentioned about Malik concerning the extension of Maghrib and Isha times until dawn is for the time of necessity, not the optional time.