Have you ever wondered why Indian astronomy consists of Navagrahas which has many differences with the western classification of 9 planets? Indians consider 5 nearest planets to Earth, along with Soorya (Sun), Chandra (Moon), Rahu and Ketu as the 9 grahas. Earth is not considered as a graha. Did you ever discard this theory without going into the roots of it? Here is the answer to all your questions.
Unlike the western system of astronomy, that considers matter as the basis of their planets, we Indians consider energy as the basis of our astronomical classification. Grahas are not equal to planets. 'Graha' is derived from the Sanskrit word 'grahana', which means to receive. Therefore, anything that affect the energy on Earth is considered a graha. According to Brahmanda-Pindaanda analysis of grahas, out of the 9 planets only the closest 5 are the ones that affect the gravitational energy on earth, namely Mangal, Budh, Guru, Shukra and Shani. These are therefore included in the Indian system of grahas.
Soorya (Sun) and Chandra (Moon) are a grahas according to this theory, since they affect earth's light and heat energy, along with the obvious gravitional force they exert on earth. The last two grahas, Rahu and Ketu cause eclipse, or 'grahanaa', meaning inability to receive. Rahu causes solar eclipse and Ketu causes lunar eclipse- two events when the energy on earth are drastically affected. This is why Rahu and Ketu are considered as chaaya grahas. They do not have any existance in the form of matter.