Seated on His chariot with Arjuna, Kṛṣṇa proceeded north, crossing over many planetary systems. These are described in Śrīmad-Bhāgavatam as sapta-dvīpa. Dvīpa means “island.” These planets are sometimes described in the Vedic literature as dvīpas. The planet on which we are living is called Jambūdvīpa. Outer space is taken as a great ocean of air, and within that great ocean of air there are many islands, which are the different planets. On each and every planet there are oceans also. On some of the planets the oceans are of salt water, and on some of them there are oceans of milk. On others there are oceans of liquor, and on others there are oceans of ghee or oil. There are different kinds of mountains also. Each and every planet has a different type of atmosphere.
Kṛṣṇa passed over all these planets and reached the covering of the universe. This covering is described in Śrīmad-Bhāgavatam as great darkness. The material world as a whole is described as dark. In the open space there is sunlight, and therefore it is illuminated, but in the covering, because of the absence of sunlight, it is naturally dark. When Kṛṣṇa approached the covering layer of this universe, the four horses which were drawing His chariot—Śaibya, Sugrīva, Meghapuṣpa and Balāhaka—all hesitated to enter the darkness. This hesitation is also a part of the pastimes of Lord Kṛṣṇa because the horses of Kṛṣṇa are not ordinary; it is not possible for ordinary horses to go all over the universe and then enter into its outer covering layers. As Kṛṣṇa is transcendental, His chariot and His horses and everything about Him are also transcendental, beyond the qualities of this material world. We should always remember that Kṛṣṇa was playing the part of an ordinary human being, and His horses also, by the will of Kṛṣṇa, played the parts of ordinary horses in hesitating to enter the darkness.
Kṛṣṇa is known as Yogeśvara, as stated in the last portion of the Bhagavad-gītā. Yogeśvaro hariḥ: all mystic powers are under His control. In our experience we can see many human beings who have yogic mystic power and who sometimes perform very wonderful acts, but Kṛṣṇa is understood to be the master of all mystic power. Therefore, when He saw that His horses were hesitant to proceed into the darkness, He immediately released His disc, known as the Sudarśana cakra, which illuminated the sky a thousand times brighter than sunlight. The darkness of the covering of the universe is also a creation of Kṛṣṇa’s, and the Sudarśana cakra is Kṛṣṇa’s constant companion. Thus He penetrated the darkness by keeping the Sudarśana cakra before Him. Śrīmad-Bhāgavatam states that the Sudarśana cakra penetrated the darkness just as an arrow released from the Śārṅga bow of Lord Rāmacandra penetrated the army of Rāvaṇa. Su means “very nice,” and darśana means “observation”; by the grace of Lord Kṛṣṇa’s disc, Sudarśana, everything can be seen very nicely, and nothing can remain in darkness. Thus Lord Kṛṣṇa and Arjuna crossed over the great region of darkness covering the material universes.
Arjuna then saw the effulgence of light known as the brahmajyoti. The brahmajyoti is situated outside the covering of the material universes, and because it cannot be seen with our present eyes, this brahmajyoti is sometimes called avyakta. This spiritual effulgence is the ultimate destination of the impersonalists known as Vedāntists. The brahmajyoti is also described as ananta-pāram, unlimited and unfathomed. When Lord Kṛṣṇa and Arjuna reached this region of the brahmajyoti, Arjuna could not tolerate the glaring effulgence, and he closed his eyes. Lord Kṛṣṇa’s and Arjuna’s reaching the brahmajyoti region is described in the Hari-vaṁśa. In that portion of the Vedic literature, Kṛṣṇa informs Arjuna, “My dear Arjuna, the glaring effulgence, the transcendental light you are seeing, is My bodily rays. O chief of the descendants of Bharata, this brahmajyoti is I Myself.” As the sun disc and the sunshine cannot be separated, Kṛṣṇa and His bodily rays, the brahmajyoti, cannot be separated. Thus Kṛṣṇa claims that the brahmajyoti is He Himself. This is clearly stated in the Hari-vaṁśa, when Kṛṣṇa says ahaṁ saḥ. The brahmajyoti is a combination of the minute particles known as spiritual sparks, or the living entities, known as cit-kaṇa. The Vedic words so ’ham, or “I am the brahmajyoti,” can also be applied to the living entities, who can also claim to belong to the brahmajyoti. In the Hari-vaṁśa, Kṛṣṇa further explains, “This brahmajyoti is an expansion of My spiritual energy.”
Kṛṣṇa told Arjuna, “The brahmajyoti is beyond the region of My external energy, known as māyā-śakti.” When one is situated within the material world, it is not possible to experience this Brahman effulgence. In other words, in the material world this effulgence is not manifested, whereas in the spiritual world it is manifested. That is the purport of the words vyakta-avyakta in the Hari-vaṁśa. In the Bhagavad-gītā it is said, avyakto ’vyaktāt sanātanaḥ: both these energies are eternally manifested.
After this, Lord Kṛṣṇa and Arjuna entered a vast spiritual water. This spiritual water is called the Kāraṇa Ocean, which means that this ocean is the origin of the creation of the material world; this place is also known as Virajā, because it is free from the influence of the three qualities of the material world. In the Mṛtyuñjaya-tantra, a Vedic scripture, there is a vivid description of this Kāraṇa Ocean, or Virajā. It is stated there that the highest planetary system within the material world is Satyaloka, or Brahmaloka, beyond which are Rudraloka and Mahā-Viṣṇuloka. Regarding this Mahā-Viṣṇuloka, it is stated in the Brahma-saṁhitā, yaḥ kāraṇārṇava-jale bhajati sma yoga-nidrām ananta-jagad-aṇḍa-sa-roma-kūpaḥ: (BS 5.47) “Lord Mahā-Viṣṇu is lying in the Kāraṇa Ocean. When He exhales, innumerable universes come into existence, and when He inhales, innumerable universes enter within Him.” In this way, the material creation is generated and again withdrawn. When Lord Kṛṣṇa and Arjuna entered the water, it appeared that there was a strong hurricane of transcendental effulgence blowing, and the water of the Kāraṇa Ocean was greatly agitated. By the grace of Lord Kṛṣṇa, Arjuna had the unique experience of being able to see the very beautiful Kāraṇa Ocean.