The nine grahasthe lights that move

The classical system recognises only what the naked eye can see, plus two calculated points. The planets Uranus, Neptune and Pluto were discovered after the tradition was established and are not used in classical Jyotisha. The nine grahas are:

Each graha also governs a weekday, which is where the Sanskrit names for the days come from. Ravivāra (Sunday), Somavāra (Monday), Maṅgalavāra (Tuesday), Budhavāra (Wednesday), Guruvāra (Thursday), Śukravāra (Friday), Śanivāra (Saturday).

The Moon’s orbit is tilted about five degrees to the ecliptic, so it crosses the road twice per cycle. These two crossing points are the lunar nodes. Solar and lunar eclipses can happen only when the Sun and Moon are near a node, which is why the old stories describe the nodes as a demon who swallows the Sun and Moon.

Rahu is the ascending node and Ketu the descending, always exactly opposite. Unlike the planets, they move backward through the zodiac, completing a circuit in about 18.6 years. They are not bodies, but calculated points. The tradition gives them a strong role in timing and in the dasha system all the same, and treats them as signs of obsession and appetite (Rahu) and of release and detachment (Ketu).

Each of the seven visible grahas rules one or two signs, the sign being its home. The Sun and the Moon rule one sign each, and the other five rule two.

A graha is considered stronger in some signs than in others. The classical scheme describes four situations. The graha is exalted (uccha) at a specific degree of one sign and debilitated (nīca) at the opposite degree. It is in its own sign (svakṣetra) when it rules the sign. And it has a moolatrikona range, a zone of especially secure strength within its own sign.

Rahu and Ketu are not listed because schools disagree. Some place Rahu’s exaltation in Vṛṣabha, others in Mithuna. These details are fixed in the texts for the seven visible grahas, but the nodes are a matter of school.

The graha also have permanent relationships with one another, described in the Bṛhat Pārāśara Horā Śāstra. A graha placed in the sign of a friend is thought to do better, and in the sign of a rival, worse.

Several authors add nuance, such as temporary friendships created by position in a particular chart. The table gives the natural relationships only.

Each graha is associated with a set of themes, called its kārakatva. These are the traditional lists, kept short. They are attributed statements. They record what the tradition holds, not what has been demonstrated.

Sources do not always agree. A careful reading names the text it relies on and treats the lists as vocabulary, not a verdict.