SB 5.16.8

uttarottareṇelāvṛtaṁ nīlaḥ śvetaḥ śṛṅgavān iti trayo ramyaka-hiraṇmaya-kurūṇāṁ varṣāṇāṁ maryādā-girayaḥ prāg-āyatā ubhayataḥ kṣārodāvadhayo dvi-sahasra-pṛthava ekaikaśaḥ pūrvasmāt pūrvasmād uttara uttaro daśāṁśādhikāṁśena dairghya eva hrasanti.
Synonyms: 
uttara-uttareṇa ilāvṛtam — further and further north of Ilāvṛta-varṣa; nīlaḥ — Nīla; śvetaḥ — Śveta; śṛṅgavān — Śṛṅgavān; iti — thus; trayaḥ — three mountains; ramyaka — Ramyaka; hiraṇmaya — Hiraṇmaya; kurūṇām — of the Kuru division; varṣāṇām — of the varṣas; maryādā-girayaḥ — the mountains marking the borders; prāk-āyatāḥ — extended on the eastern side; ubhayataḥ — to the east and the west; kṣāroda — the ocean of salt water; avadhayaḥ — extending to; dvi-sahasra-pṛthavaḥ — which are two thousand yojanas wide; eka-ekaśaḥ — one after another; pūrvasmāt — than the former; pūrvasmāt — than the former; uttaraḥ — further north; uttaraḥ — further north; daśa-aṁśa-adhika-aṁśena — by one tenth of the former; dairghyaḥ — in length; eva — indeed; hrasanti — become shorter.
Translation: 
Just north of Ilāvṛta-varṣa — and going further northward, one after another — are three mountains named Nīla, Śveta and Śṛṅgavān. These mark the borders of the three varṣas named Ramyaka, Hiraṇmaya and Kuru and separate them from one another. The width of these mountains is 2,000 yojanas [16,000 miles]. Lengthwise, they extend east and west to the beaches of the ocean of salt water. Going from south to north, the length of each mountain is one tenth that of the previous mountain, but the height of them all is the same.
Purport: 

In this regard, Madhvācārya quotes the following verses from the Brahmāṇḍa Purāṇa:

yathā bhāgavate tūktaṁ
 bhauvanaṁ kośa-lakṣaṇam
tasyāvirodhato yojyam
 anya-granthāntare sthitam

maṇḍode puraṇaṁ caiva
 vyatyāsaṁ kṣīra-sāgare
rāhu-soma-ravīṇāṁ ca
 maṇḍalād dvi-guṇoktitām
vinaiva sarvam unneyaṁ
 yojanābhedato ’tra tu

It appears from these verses that aside from the sun and moon, there is an invisible planet called Rāhu. The movements of Rāhu cause both solar and lunar eclipses. We suggest that the modern expeditions attempting to reach the moon are mistakenly going to Rāhu.