SB 5.16.1
rajovaca
uktas tvaya bhu-mandalayama-viseso yavad adityas tapati yatra casau jyotisam ganais candrama va saha drsyate.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
King Pariksit said to Sukadeva Gosvami: O brahmana, you have already informed me that the radius of Bhu-mandala extends as far as the sun spreads its light and heat and as far as the moon and all the stars can be seen.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
In this verse it is stated that the planetary system known as Bhu-mandala extends to the limits of the sunshine. According to modern science, the sunshine reaches earth from a distance of 93,000,000 miles. If we calculate according to this modern information, 93,000,000 miles can be considered the radius of Bhu-mandala. In the Gayatri mantra, we chant om bhur bhuvah svah. The word bhur refers to Bhu-mandala. Tat savitur varenyam: the sunshine spreads throughout Bhu-mandala. Therefore the sun is worshipable. The stars, which are known as naksatra, are not different suns, as modern astronomers suppose. From Bhagavad-gita (10.21) we understand that the stars are similar to the moon (naksatranam aham sasi). Like the moon, the stars reflect the sunshine. Apart from our modern distinguished estimations of where the planetary systems are located, we can understand that the sky and its various planets were studied long, long before Srimad-Bhagavatam was compiled. Sukadeva Gosvami explained the location of the planets, and this indicates that the information was known long, long before Sukadeva Gosvami related it to Maharaja Pariksit. The location of the various planetary systems was not unknown to the sages who flourished in the Vedic age.