The Study of Jyotisha · Chapter 3 of 54 · Part One · Beginnings

#How the planets move

#The nine grahas

Indian astrology works with nine moving bodies, called the grahas. The word is often translated "planets", but it really means "seizers" — things that take hold of a person, or of the sky. The nine are:

So the "nine planets" of Jyotisha are, in modern terms, one star, one moon, five planets and two mathematical points. This does not matter for astrology, which works with appearances. What matters is that all nine move along the zodiac, and that each moves in its own way. The planets discovered with telescopes — Uranus (1781), Neptune (1846) and Pluto (1930) — are not part of classical Jyotisha, and this course does not use them.

Varahamihira lists the seven visible bodies and the node in his chapter on the planets, and gives the nodes their old names: Agu and Asura for Rahu, Shikhi for Ketu (Brihat Jataka II.3, with Chidambaram Aiyar's note).

This chapter is about motion: how fast each graha moves, why some seem to turn back, when they disappear, and what the nodes are. Chapter 8 is about what each graha means. Keep the two apart in your mind. Motion is astronomy, and you can check it against the sky. Meaning is astrology, and comes from the texts.

#How fast each graha moves

All the grahas except Rahu and Ketu move eastward along the zodiac most of the time — the same direction the Sun moves through the year. But they move at very different speeds. The table gives round figures.

Three things in this table are worth remembering, because astrologers use them constantly.

1. The Moon is fast. It changes sign every two and a quarter days and nakshatra about every day. This is why the Moon is the main timekeeper of the Indian calendar (Chapter 5) and why the Moon's position is so personal: two people born a day apart can have the Moon in different nakshatras.
2. Jupiter takes about a year in each sign, and Saturn about two and a half years. Their movement through the signs is the backbone of transit reading (Chapter 24).
3. Mercury and Venus never go far from the Sun. Seen from the Earth, Mercury is never more than about 28° from the Sun, and Venus never more than about 47°. So Mercury is always in the same sign as the Sun or the sign on either side of it, and Venus is always within two signs of the Sun. If you ever see a chart with Mercury four signs away from the Sun, the chart is wrong.

#The ancient way of counting speed

The Surya Siddhanta gives each graha's speed in a striking way: as the number of times it goes round the zodiac in one great age (mahayuga) of 4,320,000 years (Surya Siddhanta I.29–34). The numbers it gives include:

• Sun: 4,320,000 revolutions
• Moon: 57,753,336
• Mars: 2,296,832
• Jupiter: 364,220
• Saturn: 146,568
• the Moon's node: 232,238, moving the "contrary" way, that is, backward

From these you can work out each period yourself. Divide 4,320,000 by the number of revolutions to get the period in years:

• Saturn: 4,320,000 ÷ 146,568 = 29.47 years
• Jupiter: 4,320,000 ÷ 364,220 = 11.86 years
• Mars: 4,320,000 ÷ 2,296,832 = 1.881 years, or about 687 days
• the node: 4,320,000 ÷ 232,238 = 18.60 years

Modern measurements give 29.46, 11.86, 1.881 years and 18.61 years. The ancient figures are astonishingly close. They were not guesses. They came from centuries of careful observation, and they are one of the great achievements of Indian science. (For Mercury and Venus the Surya Siddhanta's scheme is different, because those two stay close to the Sun; the details belong to Chapter 49.)

#Why planets seem to go backward

Watch Mars over a few months and something strange happens. It moves eastward among the stars, slows down, stops, moves westward for a few weeks, stops again, and then carries on eastward. This backward motion is called retrogression. In Sanskrit a planet in retrograde motion is vakra, "crooked" or "bent", and a planet moving forward normally is margi, "on its path". The points where the planet seems to stand still are called its stations.

Nothing actually reverses. Retrogression is an effect of watching from a moving Earth.

For Mars, Jupiter and Saturn (the planets farther from the Sun than the Earth): the Earth, on its smaller and faster orbit, regularly overtakes them. Think of driving on a highway and overtaking a slower car. For a moment, against the distant hills, the slower car seems to slide backward. In the same way, when the Earth passes between the Sun and an outer planet, the planet seems to slide backward against the distant stars. So an outer planet is retrograde when it is roughly opposite the Sun in the sky — which is also when it is closest to the Earth and brightest.

For Mercury and Venus (the planets closer to the Sun than the Earth): they move faster than the Earth and overtake it. They appear retrograde when they pass between the Earth and the Sun — that is, when they are near the Sun in the sky, at the point called inferior conjunction.

The Sun and the Moon are never retrograde. Rahu and Ketu, as most Indian astrologers compute them (the "mean" nodes), are always retrograde: they always move backward through the zodiac.

How often each planet goes retrograde, in round figures:

The Surya Siddhanta names eight kinds of planetary motion, from "very swift" through "even" to "very slow", and then "somewhat retrograde" and "retrograde" (Surya Siddhanta II.12–13). Burgess notes that the text names these kinds but hardly uses them afterward. Astrology uses mainly the simpler pair, forward and retrograde, plus the fact that a planet near its station is moving very slowly.

Why astrologers care. The classical texts give a retrograde planet special strength. In the system of planetary strength called cheshta bala, "strength of motion", a retrograde planet gets the highest score, because when it is retrograde it is closest to the Earth and brightest (Chapter 14). Varahamihira says he treated the planets' "retrograde and re-retrograde motions" in his book on astronomy (Brihat Samhita I.10), and he lists them among the things a true astrologer must know (Brihat Samhita II). Popular astrology today often treats retrogression as unlucky; that view is not in the classical texts, which mostly treat a retrograde planet as strong.

#When a planet disappears: combustion

A planet close to the Sun in the sky cannot be seen — it is lost in the Sun's glare. In the evening a planet sinks into the twilight and vanishes; some weeks later it reappears in the morning twilight on the other side of the Sun. The disappearance is called the planet's heliacal setting, and the reappearance its heliacal rising. In Sanskrit a planet hidden by the Sun is asta, "set", and in astrology it is called combust (from Latin, "burnt").

The Surya Siddhanta gives the distance from the Sun at which each planet disappears or reappears. In Burgess's translation (Surya Siddhanta IX.6–9):

The text explains that within these distances the planets' forms are "swallowed up" by the brightness of the Sun (Surya Siddhanta IX.9). The Moon's own rule is in the next chapter: it becomes visible or invisible at 12° from the Sun (Surya Siddhanta X.1).

Strictly, these distances are measured in "degrees of time" — the time difference between the planet's setting and the Sun's setting, turned into degrees — and not in degrees of longitude along the zodiac. Later astrological books took over the same numbers as plain distances in longitude, and that is how most astrologers use them today: a planet within that many degrees of the Sun is called combust. This is a good example of a rule that changed meaning slightly as it passed from the astronomers to the astrologers.

Why astrologers care. A combust planet is generally treated as weakened in the classical texts, as if its light were taken over by the Sun. Chapter 15 gives the details. Notice again that this rule rests on something you can check with your own eyes: a combust planet really cannot be seen.

#Planetary war

When two of the five visible planets (Mars, Mercury, Jupiter, Venus and Saturn) come very close together in the sky, the Indian astronomers called the meeting a graha yuddha, a "planetary war". The Sun and Moon do not take part.

The Surya Siddhanta classifies these close meetings (Surya Siddhanta VII.1, 18–23):

• when the two planets are less than a degree apart, it is a war;
• when they are more than a degree apart and both are bright, it is a peaceful meeting (samagama);
• in a war, the loser is the planet that looks rough, colourless or faint and is on the south side; the winner is the one on the north side that is bright and large — or even on the south side if it is strong;
• Venus is generally the winner, whether north or south.

Why astrologers care. A planet that loses a planetary war is treated as weakened, and a winner as strengthened (Chapter 15). Some modern astrologers judge the winner simply by which planet has the higher latitude, or which is brighter; others by which is further north. Notice that the rule depends on latitude — how far north or south of the ecliptic each planet is — which is why Chapter 2 mentioned latitude at all.

#Rahu and Ketu: the nodes of the Moon

The Moon's orbit is tilted about 5° to the ecliptic. So twice a month the Moon crosses the ecliptic: once going north and once going south. These two crossing points are the Moon's nodes:

• Rahu is the north node (also called the ascending node), where the Moon crosses the ecliptic going north.
• Ketu is the south node (the descending node), where the Moon crosses going south.

The two are always exactly opposite each other — 180° apart. If Rahu is at 10° Taurus, Ketu is at 10° Scorpio.

The nodes are not fixed. They slide slowly backward (westward) round the zodiac, taking about 18⅔ years for a full circle. This is why they are always retrograde. The Surya Siddhanta gives the node's motion as 232,238 revolutions in an age, "in the contrary direction" (Surya Siddhanta I.33).

#Mean nodes and true nodes

The node's motion is not perfectly smooth. Its average position is called the mean node; its exact, wobbling position at a given moment is called the true node. The two can differ by up to about a degree and a half. Most Indian almanacs and astrologers use the mean node, which is why it always moves backward. Some software uses the true node, which now and then stands still or even moves forward for a few days. This is another convention to check when two charts disagree. The calculators on this website use the mean node.

#Rahu in myth and in astronomy

The old story says that Rahu was a demon (asura) who disguised himself to drink the nectar of immortality. The Sun and Moon recognised him, and Vishnu cut off his head — but the head had already tasted the nectar and so lived on. Rahu, the head, and Ketu, the body, are said to swallow the Sun and Moon in revenge, causing eclipses.

What is remarkable is how firmly Varahamihira, writing in the sixth century, rejected the literal version of this story. In a chapter of the Brihat Samhita titled "On Rahu", he first reports what "some say" — that Rahu is a planet with a black disc, or a serpent, or mere darkness. Then he asks a series of sharp questions: if Rahu has a body moving along the ecliptic, how can he eclipse the Moon when he is 180° away from it? Why does he never eclipse with the middle of his body? And he gives the answer plainly (Brihat Samhita V.8–13):

• in a lunar eclipse the Moon enters the shadow of the Earth;
• in a solar eclipse the Moon covers the disc of the Sun, "just like a cloud";
• what eclipses the Moon is bigger than the Moon, and what eclipses the Sun is smaller than the Sun;
• "Rahu does not cause the eclipse" — that, he says, is the truth of the sciences.

He keeps Rahu as the name of the ascending node and as an object of worship at eclipse time, but as a point, not a monster (Brihat Samhita V.14–15). This is a beautiful example of the critical spirit inside the tradition. It is also exactly how this course treats Rahu and Ketu: as real points in the sky with real astronomical meaning, around which a large body of astrological interpretation has grown.

#Eclipses

An eclipse needs two things at once:

1. a new moon or a full moon — the Sun and Moon in the same place (new moon) or exactly opposite (full moon); and
2. the Moon near one of its nodes, so that it is on or very close to the ecliptic.

Most months the Moon passes a little north or south of the Sun at new moon, or of the Earth's shadow at full moon, and there is no eclipse. Only when a new or full moon happens near Rahu or Ketu do the three bodies line up.

• At a solar eclipse (new moon near a node), the Moon passes in front of the Sun. It is seen only from a strip of the Earth's surface, and looks different from place to place, as Varahamihira notes (Brihat Samhita V.11).
• At a lunar eclipse (full moon near a node), the Moon passes through the Earth's shadow. It can be seen from the whole night side of the Earth at once.

Eclipses come in "seasons" about every six months, when the Sun passes the nodes. Because the nodes move backward, these seasons come a little earlier each year. In India eclipses have always been times of ritual — bathing, charity and prayer — and the Samhita branch of Jyotisha has much to say about them (Chapter 42). The calendar on this website computes every eclipse for your location and checks them against NASA's published tables.

#Conjunctions and oppositions

Two last words, used in every chapter from here on:

• A conjunction (yuti or samagama) is when two grahas are at the same longitude, or close to it. In Indian astrology, two grahas in the same sign are usually said to be "together" or "conjoined", even if they are not at the same degree.
• An opposition is when two grahas are 180° apart. In Indian astrology, two grahas in opposite signs (the 1st and 7th from each other) are said to be in mutual aspect (Chapter 11).

The Surya Siddhanta gives a whole method for finding the exact moment two planets reach the same longitude: divide the distance between them by the difference of their daily motions if both are moving the same way, or by the sum if one is retrograde (Surya Siddhanta VII.2–4). This is simple arithmetic you can try yourself.

Example. Venus is at 10°00′ Aries moving 1°12′ a day. Jupiter is at 13°00′ Aries moving 0°12′ a day. Both are moving forward. The gap is 3°00′ = 180′. The difference in speed is 72′ − 12′ = 60′ a day. Venus catches Jupiter in 180 ÷ 60 = 3 days, at about 13°36′ Aries.

#Summary

• Jyotisha uses nine grahas: Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn, and the Moon's nodes Rahu and Ketu. Uranus, Neptune and Pluto are not part of the classical system.
• Speeds differ greatly: the Moon changes sign every 2¼ days, Jupiter every year, Saturn every 2½ years. Mercury and Venus stay close to the Sun.
• The Surya Siddhanta's periods, given as revolutions in a great age, match modern values very closely (Surya Siddhanta I.29–34).
• Retrogression (vakra) is an apparent backward motion seen from the moving Earth. Outer planets are retrograde when opposite the Sun; Mercury and Venus when between the Earth and the Sun. The Sun and Moon never; the mean nodes always.
• A planet too close to the Sun is invisible, asta, "combust". The Surya Siddhanta gives the distances: Jupiter 11°, Saturn 15°, Mars 17°, Venus 8° or 10°, Mercury 12° or 14° (Surya Siddhanta IX.6–9).
• Two planets within a degree are in "planetary war"; the winner is the brighter, northern one (Surya Siddhanta VII.18–23).
• Rahu and Ketu are the Moon's north and south nodes, always opposite, moving backward round the zodiac in about 18⅔ years. Varahamihira explained eclipses as the Earth's shadow and the Moon's disc, not a demon (Brihat Samhita V.8–13).

#Exercises

1. Mercury is at 2° Taurus. In which signs could the Sun possibly be?
2. Saturn is retrograde. Roughly where in the sky is the Sun, compared to Saturn?
3. Rahu is at 24°30′ Leo. Where is Ketu?
4. Using the Surya Siddhanta's number for the Moon (57,753,336 revolutions in 4,320,000 years), work out how many times the Moon goes round the zodiac in one year. How many days is that per revolution, taking a year as 365¼ days?
5. Mars is at 20°00′ Gemini moving 0°40′ a day. Saturn is at 21°30′ Gemini moving 0°04′ a day. Both are moving forward. When will they meet, and will it be a "planetary war"?

Answers: 1. The Sun must be within about 28° of Mercury, so in Aries, Taurus or Gemini. 2. Roughly opposite Saturn. 3. 24°30′ Aquarius. 4. 57,753,336 ÷ 4,320,000 ≈ 13.37 revolutions a year; 365.25 ÷ 13.37 ≈ 27.3 days. 5. Gap 1°30′ = 90′; speed difference 36′ a day; they meet in 2½ days. Whether it is a war depends on their latitudes — if they pass within a degree of each other in the sky, yes.