|Picture Credit: Amar D.Gupta|
The Hinduism which we practice today is a consolidation of various matham (religion). Each matham has one primary God and it can be considered as monotheistic.
The traditional 6 religion which were said to be grouped together by Adi Sankara are known as Shaivam, Shaktam, Vaishnavam, Ganapatyam, Kaumaram and Sauram.
The primary God of Shaivam is Shiva, for Shaktam it is Shakti, for Vaishnavam it is Vishnu, for Ganapatyam it is Ganapathi, for Kaumaram it is Kumara (Muruga) and for Sauram it is Surya (Sun).
These 6 religions are collectively called as ShanMatham.
Shan is the Sanskrit word for the number 6.
There is also a tradition known as Smartham. The Smarthas worship God as ParaBrahma and accept the forms of God in the other mathams. Smarthas can worship any one of the primary God from ShanMatham as their favourite deity or IsthaDeivam. The present form of mainstream Hinduism is influenced by the Smartham tradition.
There is a phrase in Tamil, "Emmathamum Sammathum" meaning "Any religion is accepted". Many Tamils use this phrase in reference to religious tolerance. This is actually wrong.
The actual phrase is "En Mathamum ShanMatham" meaning "My Religion Is Also The 6 Religion". This means a person who use this phrase believe in one of the 6 traditional Hindu religions as stated above. So this phrase is only applicable for the 6 religions within Hinduism.
The worship of NavaGraha (9 planets/celestial objects) is part of the Sauram religion. In the NavaGraha worship, Surya takes the central position. He is the primary God. Surya is accompanied by Chandran (Moon), Chevvai (Mars), Budhan (Mercury), Viyalan or Guru (Jupiter), Shukran (Venus), Sani (Saturn), Rahu (North Lunar Node) and Ketu (South Lunar Node).
You would have been advised by some Gurukkal to offer lamp for Sani (Saturn) on Saturdays. Saturday is the day of Saturn, hence Saturn's Day became Saturday. In Tamil we call it as Sani Kilamai. Some devotees offer lamp for other purpose on Thursday for Guru (Jupiter).
The followers of other religions such as Shaivam have their own ways of doing things. A Shaiva would normally offer prayers to Shiva in the form of Dhakshinamoorthy on Thursdays instead of offering prayers to Guru (Jupiter).
The Shaivas, Shaktas, Vaishnavas, Ganapatyas and Kaumaras also believe in total surrender to their respective primary forms of God. Surrendering to God and worshipping with sincerity is the ultimate form of Bhakthi in these religions.
NavaGraha worship of the Sauram religion is closely associated with Jyotisha (Astrology) as each graha plays a role in a person's birth chart. Astrology is based on the study of Astronomy and how it relates to a human's life.
Although NavaGraha worship is part of Sauram, it is also practised by a large number of Hindus who follow the other remaining 5 religious schools.