Graha (from Sanskrit ग्रह gráha -- seizing, laying hold of, holding) is a 'cosmic influencer' on the living beings of mother Bhumidevi (earth). In Hindu Astrology, the Navagraha (Sanskrit: नवग्रह, nine planets or nine realms) are some of these major influencers.
"The Sanskrit word captures the idea that these nine grahas are living energies which put out waves of energy. These waves of energy affect our awareness. ... this indicates ... the active power of these celestial energies to seize our consciousness when we come under their influence or to take hold of what we focus on."
Accordingly to some, Grahas are the "markers of influence", that point out the karmic influence on the behavior of living beings. They themselves are not causative elements but can be compared to traffic signs.
Unfortunately, the term Graha was linked to the term "planet" of our solar system, as five members of Navagraha (the nine grahas) happen to be planets; but the Surya (sun), Chandra (moon), Rahu (north or ascending lunar node) and Ketu (south or descending lunar node) are not "planets" according to modern astronomy. This misconception is sometimes used as arguments against the validity of astrology. However, a fact common to all the navagraha is that they have relative movement with respect to the background of fixed stars in the zodiac.
"Graha" is sometimes also translated as "celestial body", but Rahu and Ketu are not celestial bodies either, but are only positions in the lunar path. A third translation is celestial god or demi-god, but again, Rahu and Ketu are demonic Asuras , not benign deities like Devas. Thus the term 'graha' in this contexts applies to the nine (9) planetary or cosmic deities, spirits, spiritual beings-entities, etc. The term however mostly refers to any spirit(ual) force in general.
Indeed, according to the astrological treatise Prasna Marga there are many other spiritual entities called grahas or spirits. All (excepting the navgrahas) are said to have been born of the anger of Lord Shiva or Rudra. Most grahas are generally malefic in nature but there are a few that may be good. The book called The Puranic Encyclopedia, under the heading 'Graha Pinda', gives a list of such grahas (spirits or spiritual entities, etc), that are said to afflict children, etc. Also in the same book in various places the names of spirits (grahas) are given, like 'Skhanda graha' that is said to cause miscarriage(s),
 Connections to energies/mantras
Reports of psychics / energy readers affirm that Grahas are causing direct energy influence upon the auras (energy bodies) and minds of beings connected to the Earth (like humans, animals, plants etc.) Each Graha carries a specific energy quality, which is described in an allegorical form through its mythological and astrological references. "... cosmic energy we always receive contains different energies coming from different celestial bodies..." The energies of the Grahas are getting connected in a specific way to the individual auras of humans at the time they take their first breath in a given nativity. These energy connections remain with the natives of Earth as long as their current body lives. "... The nine planets are transmitters of universal, archetypal energy. The qualities of each planet help to maintain the overall balance of polarities in both the macrocosmic and the microcosmic universe - as above, so below..." Earth (as an independent energy entity) and its rotation around its axis is an important mediator and deciding factor of how these influences are carried out upon the beings, who are the children of Earth. See more in the Jyotisha Bhavas (also as a section under Hindu Astrology) . Humans are also capable to tune themselves to the chosen energy of a specific Graha through Samyama with that Graha or its presiding deity. The effects of worship of specific deities are manifested accordingly to the layout of their relative energies in a given nativity of a worshipper in question. "... When we repeatedly utter a Mantra we are tuning to a particular frequency and this frequency establishes a contact with the cosmic energy and drags it into our body and surroundings..."
The idea of planets, stars and other celestial bodies being the living energy entities influencing the other beings of the Universe has cross-references in many ancient cultures and had become the background of numerous modern fiction works (like Solaris by Stanisław Lem, see also the movie with the same title).
The Navagraha are personified as celestial beings and worshipped as deities.
The worship of Sun (the king of the Grahas) as a personified being is common for most of ancient religions and spiritual traditions, Hinduism being a bright example of it. Many of classical Jyotisha scriptures (like Brihat Parashara Hora Shastra, Kalyana Varma's Saravali etc. etc.) start with an invocation of Sun-God (Surya). Other Grahas are commonly considered to be the living members of Surya's court and are being addressed personally in order to gain help in their respective areas of influence.
In several parts of India, there are clusters of Navagraha temples. One such cluster is near the town of Kumbakonam, Tamil Nadu; another temple is in Guwahati, Assam.
 See Also