text: Zodiac and calendar Soma is the root of the word Somavara or Monday in the Hindu calendar. The word "Monday" in the Greco-Roman and other Indo-European calendars is also dedicated to the Moon. Soma is part of the Navagraha in the Hindu zodiac system. The role and importance of the Navagraha developed over time with various influences. Deifying the moon and its astrological significance occurred as early as the Vedic period and was recorded in the Vedas. The earliest work of astrology recorded in India is the Vedanga Jyotisha which began to be compiled in the 14th century BCE. The moon and various classical planets were referenced in the Atharvaveda around 1000 BCE.
  The Navagraha was furthered by additional contributions from Western Asia, including Zoroastrian and Hellenistic influences. The Yavanajataka, or 'Science of the Yavanas', was written by the Indo-Greek named "Yavanesvara" ("Lord of the Greeks") under the rule of the Western Kshatrapa king Rudrakarman I. The Navagraha would further develop and culminate in the Shaka era with the Saka, or Scythian, people. Additionally the contributions by the Saka people would be the basis of the Indian national calendar, which is also called the Saka calendar.
  The Hindu calendar is a lunisolar calendar which records both lunar and solar cycles. Like the Navagraha, it was developed with the successive contributions of various works.