What is the meaning of the Almighty’s saying: "And if We had opened upon them a gate from the heaven and they continued therein to ascend," and what is meant by "heaven" here, and is the verse connected to the ascent of astronauts today?

It is not appropriate to interpret the words of the Quran and Sunnah according to modern terminology in astronomy and physics, nor to restrict the meaning of divine revelation to a narrow sense limited by its environment or time. Ibn al-Jawzi, in Zad al-Masir, discussed the meaning of the Almighty's saying: "And even if We opened to them a gate from the heaven and they continued ascending through it, they would surely say, 'Our eyes have been bewitched; rather, we are a people affected by magic.'" [Al-Hijr: 14, 15]. He mentioned two opinions regarding those referred to as ascending: either the angels or the polytheists.

The verse illustrates the obstinacy of the disbelievers and that they would not believe even if they saw a great sign, which God Almighty affirmed in other verses. As for the phrase "a gate from the heaven" and its relation to space exploration, researcher Huda Al-Zaydi addressed it in her doctoral dissertation. She referred to the words of the first astronaut, Gagarin, who saw the darkness of cosmic space and expressed, "What do I see? Am I dreaming or have my eyes been bewitched?" This aligns with what the Quran mentioned. She pointed out that the "if" (لو) in the verse indicates a hypothesis that will not materialize for those concerned by the verse, but it signifies the possibility of opening the way.

The intended meaning of "heaven" here is one of the heavens, as mentioned by Dr. Fadil Salih al-Samarra'i, and not everything above you, because the context indicates this by mentioning "a gate from the heaven." The heavens have gates, as stated in the hadith of Al-Isra and Mi'raj, and modern discoveries confirm that this phenomenon occurs merely 200 kilometers above the Earth's surface.