Of the Four Vedas, Rig, Yajur, Sama and Atharva,Yajur veda has two aspects.
Krishna Yajur and
The Shukla Yajur Mantras are longer and more detailed.
The reason attributed is that though these Mantras have been revealed by Lord Surya, The Sun God directly to Sage Yajnyavalkya, as these Mantras were not initiated by a Guru, as recommended by the Vedas, more Mantras are provided to compensate the issue of not being initiated bya Guru.
Yajnyavalkya was a Disciple of Vaisampayana.
The Sages used to meet often to exchange views on the Vedas, much like the Academics of today.
On one such occasion, Vaisampayana asked one of his disciples(Not Yajnyavalkya) to represent him.
Yajnavalkya informed the Guru that he would represent him and he argued with Vaisampayana on this issue.
Annoyed Vaisampayana admonished Yajnavalkya for questioning the Guru, being argumentative and advised Yajnyavalkya to leave after returning the Vedas he had learnt.
Yajnavalkya is the first recorded Sage in History.
As per the demands of his Guru, Yājñavalkya vomited all the knowledge that he acquired from his teacher in form of digested food. Other disciples of Vaisampayana took the form ofpartridge birds and consumed the digested knowledge (a metaphor for knowledge in its simplified form without the complexities of the whole but the simplicity of parts) because it was knowledge and they were very eager to receive the same.
The Saṃskṛt name for partridge is “Tittiri”. As the Tittiri (partridge) birds ate this Veda, it is thenceforth called the Taittirīya Yajurveda. It is also known as Kṛṣṇa Yajurveda or Black-Yajurveda on account of it being a vomited substance. The Taittirīya Saṃhitā thus belongs to this Yajurveda.
Then Yājñavalkya determined not to have any human guru thereafter. Thus he began to propitiate the Sun God, Surya. Yājñavalkya worshipped and extolled the Sun, the master of the Vedas, for the purpose of acquiring the fresh Vedic portions not known to his preceptor, Vaiśampāyana.
The Sun God, pleased with Yājñavalkya penance, assumed the form of a horse and graced the sage with such fresh portions of the Yajurveda as were not known to any other. This portion of the Yajurveda goes by the name of Śukla Yajurveda or White-Yajurveda on account of it being revealed by Sun. It is also known as Vajasaneya Yajurveda, because it was evolved in great rapidity by Sun who was in the form of a horse through his manes.The rhythm of recital of these vedas is therefore to the rhythm of the horse canter and distinguishes itself from the other forms of veda recitals. In Sanskrit, term “Vaji” means horse. Yājñavalkya divided this Vajasaneya Yajurveda again into fifteen branches, each branch comprising hundreds of Yajus Mantras. Sages like Kanva, Madhyandina and others learnt those and Śukla Yajurveda branched into popular recensions named after them.
It is important to note that within the hierarchy of Brāhmaṇas, certain sects believe in the Kṛṣṇa Yajurveda while others practice from the Śukla Yajurveda.
Yājñavalkya married two wives. One was Maitreyi and the other Katyaayanee. Of the two, Maitreyi was a Brahmavadini (one who is interested in the knowledge of Brahman).The descendant sects of Brahmans are the progeny of the first wife Katyaayanee. When Yājñavalkya wished to divide his property between the two wives, Maitreyi asked whether she could become immortal through wealth. Yājñavalkya replied that there was no hope of immortality through wealth and that she would only become one among the many who were well-to-do on. When she heard this, Maitreyi asked Yājñavalkya to teach her what he considered as the best. Then Yājñavalkya described to her the greatness of the Absolute Self, the nature of its existence, the way of attaining infinite knowledge and immortality, etc. This immortal conversation between Yājñavalkya and Maitreyi is recorded in the Brihadaranyaka Upanishad.
Wisdom of Yājñavalkya is shown in Brhadaranyaka Upanishad where he gives his teachings to his wife Maitreyi and King Janaka. He also participates in a competition arranged by King Janaka about the selecting great Brhama Jnani (knower of Brahman). His intellectual dialogues with Gargi (a learned scholar of the times) form a beautiful chapter filled with lot of philosophical and mystical question-answers in Brhadaranyaka Upanishad. He was then praised as the greatest Brahmajnyani by all the sages at the function organised by king Janaka. In the end, Yājñavalkya took Vidvat Sanyasa (renunciation after the attainment of the knowledge of Brahman) and retired to the forest..
This deals more with the Karma Kanda, performance of Rituals.
The Shatapatha Brahmana (शतपथ ब्राह्मण śatapatha brāhmaṇa, “Brahmana of one hundred paths”, abbreviated ŚB) is one of the prose texts describing the Vedic ritual, associated with the Shukla Yajurveda. It survives in two recensions, Madhyandina (ŚBM, of the vājasaneyi madhyandina śākhā) and Kanva (ŚBK, of the kāṇva śākhā), with the former having the eponymous 100 chapters (adhyayas), 7,624 kandikas (parts) in 14 books, and the latter 104 chapters, 6,806 kandikas in 17 books.
Linguistically, the Shatapatha Brahmana belongs to the later part of the Brahmana period of Vedic Sanskrit (i.e. roughly the 8th to 6th centuries BCE, Iron Age India).
Jan N. Bremmer dates it to around 700 BCE. According to Julius Eggeling, the final version of the text was committed in 300 BCE, although some of its portions are “far older, transmitted orally from unknown antiquity”.
Among the points of interest in the text are its mythological sections, including the myths of creation and the Deluge of Manu.The creation myth has several similarities to other creation myths, including the use of primordial water (similar to the Bible), the explanation of light and darkness, the separation of good and evil, and the explanation of time. The text describes in great detail the preparation of altars, ceremonial objects, ritual recitations, and the Soma libation, along with the symbolic attributes of every aspect of the rituals.
The 14 books of the Madhyandina recension can be divided into two major parts. The first 9 books have close textual commentaries, often line by line, of the first 18 books of the corresponding samhita of the Yajurveda. The following 5 books cover supplementary and ritualistically newer material, besides including the celebrated Brhadaranyaka Upanishad as most of the 14th and last book.
The Shatapatha Brahmana of Madhyandina School was translated into English by Julius Eggeling, in the late 19th century, in 5 volumes published as part of the Sacred Books of the East series. The English translation of Kanva School was done by W.E. Caland in 3 parts.