Fast and slow grahas
Grahas are sometimes grouped by speed: the Moon is the fastest, then Mercury and Venus, then the Sun and Mars, and Jupiter and Saturn are the slowest.
What it is
The Moon crosses a sign in about two and a half days, Mercury and Venus in roughly a month, the Sun in a month, Mars in about six weeks, Jupiter in a year and Saturn in about two and a half years.
How it is worked out or read
The classical texts use speed in several ways, including for retrograde and combustion. The site computes positions from the library, so speed follows from the model.
Where it appears on this site
See the planetary speed table and transits.
Average daily motions
The grahas move at very different speeds against the zodiac. On average, the Moon moves about 13 degrees a day, the fastest by far. The Sun moves about one degree a day. Mercury and Venus average about one degree a day as well, because they stay near the Sun, but each can move faster or slower and can turn retrograde. Mars averages about half a degree a day. Jupiter moves about five minutes of arc a day, and Saturn about two. Rahu and Ketu, the lunar nodes, move backwards at about three minutes of arc a day on average.
These figures are averages. The actual daily motion of every graha except the nodes varies through its cycle, and the variation is largest for Mercury, Venus and Mars.
Time spent in each sign
The same speeds give the approximate time each graha spends in one sign. The Moon stays about two and a quarter days; the Sun about a month; Mercury and Venus roughly a month each, though retrograde periods can extend this; Mars about a month and a half on average, but up to six months or more when it turns retrograde; Jupiter about a year; Saturn about two and a half years; and Rahu and Ketu about eighteen months. These durations explain why the Moon is used for daily readings and Jupiter and Saturn for long-term trends.
The classical categories of motion
Classical texts describe several states of a planet's motion rather than a single speed. The lists vary, but they commonly include vakra, retrograde; anuvakra, moving retrograde into the previous sign; vikala, stationary; manda and mandatara, slow and slower than average; sama, average; and chara and atichara, fast and very fast. These states are used in calculating cheshta bala, the motional strength of a planet, in which a retrograde planet is traditionally given high strength.
Fast and slow in reading
Speed also enters interpretation. A slow-moving planet, especially one near its station, is traditionally thought to express its themes more strongly or persistently, because it stays near the same degree for a long time. A fast-moving Moon at birth is sometimes read as quick in response, and a slow Moon as steady. These are traditional interpretive ideas rather than measurements, and different readers weight them differently.
Seeing the speeds on this site
The planet table on the birth chart page shows each graha's sign, degree and nakshatra, with a column saying whether it is retrograde. Comparing two charts made a day apart shows the speeds directly: the Moon will have moved about 13 degrees, the Sun about one, and Saturn hardly at all. This simple exercise makes the speed categories concrete.