I find Bahá’u’lláh’s teachings on the meaning of celestial imagery in the Qur’án very illuminating.
“And now, concerning His words—“The sun shall be darkened, and the moon shall not give light, and the stars shall fall from heaven.” By the terms “sun” and “moon,” mentioned in the writings of the Prophets of God, is not meant solely the sun and moon of the visible universe. Nay rather, manifold are the meanings they have intended for these terms”.
“The term “suns” hath many a time been applied in the writings of the “immaculate Souls” unto the Prophets of God, those luminous Emblems of Detachment. Among those writings are the following words recorded in the “Prayer of Nudbih”: “Whither are gone the resplendent Suns? Whereunto have departed those shining Moons and sparkling Stars?” Thus, it hath become evident that the terms “sun,” “moon,” and “stars” primarily signify the Prophets of God, the saints, and their companions, those Luminaries, the light of Whose knowledge hath shed illumination upon the worlds of the visible and the invisible”.
“In another sense, by the terms ‘sun’, ‘moon’, and ‘stars’ are meant such laws and teachings as have been established and proclaimed in every Dispensation, such as the laws of prayer and fasting. These have, according to the law of the Qur’án, been regarded, when the beauty of the Prophet Muḥammad had passed beyond the veil, as the most fundamental and binding laws of His dispensation. To this testify the texts of the traditions and chronicles, which, on account of their being widely known, need not be referred to here. Nay rather, in every Dispensation the law concerning prayer hath been emphasized and universally enforced. To this testify the recorded traditions ascribed to the lights that have emanated from the Day-star of Truth, the essence of the Prophet Muḥammad”.
“Muḥammad, the Seal of the Prophets, and the most distinguished of God’s chosen Ones, hath likened the Dispensation of the Qur’án unto heaven, by reason of its loftiness, its paramount influence, its majesty, and the fact that it comprehendeth all religions. And as the sun and moon constitute the brightest and most prominent luminaries in the heavens, similarly in the heaven of the religion of God two shining orbs have been ordained—fasting and prayer. ‘Islám is heaven; fasting is its sun, prayer, its moon.’”
“This is the purpose underlying the symbolic words of the Manifestations of God. Consequently, the application of the terms “sun” and “moon” to the things already mentioned hath been demonstrated and justified by the text of the sacred verses and the recorded traditions. Hence, it is clear and manifest that by the words “the sun shall be darkened, and the moon shall not give her light, and the stars shall fall from heaven” is intended the waywardness of the divines, and the annulment of laws firmly established by divine Revelation, all of which, in symbolic language, have been foreshadowed by the Manifestation of God”.