All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
We did not find a text that specifies exactly what is meant by that distance. However, there is a rule that the Muslim should abide by when dealing with texts of the Revelation (Quran and Sunnah), namely, it is not permissible to interpret the meaning of the texts in a way that is not apparently perceivable, particularly at the time of revelation. This is a principle, and it is not permissible to change it except with clear evidence that requires otherwise. In this case, we do not know any evidence indicating otherwise. Therefore, the distance, which is 500 years travel, or any other distances mentioned in some Hadeeths refer to the distance that a traveler covers walking on foot or by camel, which is a moderate speed. Terminologies of Sharee'ah should be understood in the manner which was customarily known at the time of legislation [time of the Prophet, sallallaahu ‘alayhi wa sallam]. This is the original rule. If scientific facts certainly demonstrated, for instance, that the distance is 500 light years, this would be a justification to change the meaning of the text from what was perceivable at the time of Revelation into the current facts. The Revelation addresses humanity from the first day it was sent down up to the Day of Resurrection.
Allaah Knows best.