Introduction to Astronomy

Solar-system astronomy forms the basis of the astrological discipline, and it is really important that you have a sound and very practical knowledge of how our special unit of the Milky Way galaxy works. Here we set out the basic astronomical facts about the solar system. Assimilate them, along with the instructions on calculating the birth chart, for these are the bare bones of astrology; if you make an error in these early stages then the whole of your birth chart will be inaccurate - and so will your interpretation.

All astrologers should understand certain elements of astronomy, so here we give the simplest possible explanation of certain phenomena and terms that you will need to understand.

Astronomy and astrology went hand in hand for many millennia. Man's preoccupation with the skies began long before the invention of writing, so we can only guess at the extent of the early astronomical knowledge. But as long as 6,000 years ago Chaldean priests used watchtowers to make maps of the skies, and clay tablets dating from 3800 BC record with extraordinary accuracy the motions of the Sun and the Moon.

Astronomy and astrology (one word was originally used for both sciences) no doubt began out of a marriage of curiosity and the belief that the heavens influenced the Earth. It seems rational to suppose that the Moon, the largest heavenly body, attracted much attention from the start, and that quite apart from such obvious lunar effects as those upon the tides and the menstrual cycle, Man soon noticed the effect of the Moon on sexuality.

Then came the realization that among the fixed stars - which seemed to revolve about the Earth but were stationary in relation to each other - five rogue stars rambled in what must at first have seemed illogical motion. Some lumbered slowly about the sky, some seemed almost to dart between their fellows, each revolving about the Earth in the same direction as the fixed stars, but also confined to a narrow lane - the ecliptic - that looped around the Earth at an angle of approximately 230 to the equator.

Gradually (and the history of the zodiac is a fascinating study of its own) astrologers divided the belt of the ecliptic into 12 sections, naming each after the constellation of fixed stars that stood "behind" it. Furthermore, it was realized that when a planet passed through one of the sections, certain effects occurred: babies born at that time seemed to share common characteristics, and certain events seemed more likely to occur.

Early astronomers For the next 4,500 years or more, astrologers/ astronomers studied the nature of the solar system and the apparent relationship between events in the heavens and events on Earth: the great civilizations of Egypt and Greece contributed to the theory and elaborated on it, working at the same time on purely astronomical theory and on astrology. (The great astronomer Claudius Ptolemy, for instance, not only compiled an astounding catalogue of no less than 1,022 stars, but left us the earliest surviving astrological textbook, the Tetrabiblos, written between AD 139 and 161. )

From the earliest times until about the beginning of the eighteenth century, it scarcely ever occurred to astronomers not to study astrology as well - although they had differing notions of its application and the extent of its influence. Those great astronomers of the sixteenth century who so enlarged man's understanding of the solar system - scientists that include Galileo, Kepler, Copernicus and Tycho Brahe - all regarded astrology as an important part of their discipline. The break came, substantially, with the understanding that the Sun, and not the Earth, stands at the center of the solar system. This theory was accompanied, during the Age of Enlightenment, by the increasing doubt that human. life was affected by planetary influences.

The discovery of the 'modern" planets - Uranus and Neptune, first sighted by astronomers since the middle of the eighteenth century - seemed to direct another body blow at the astrological theory (although this was no more the case than Harvey's discovery of the circulation of the blood striking a body blow at medicine!).

In 1930 and 1977 respectively, two tiny planets, Pluto and Chiron (half planet, half comet) were added to the stem's family. When interest in astrology was revived early in the twentieth century, it was fuelled by the new art of psychology rather than by astronomers, most of whom usually remain implacably opposed to the science from which their own existence sprang.

It is interesting to note that criticism of astrology by modern astronomers springs almost entirely from ignorance; few take the trouble to study the subject before condemning it. With a few honorable exceptions, astronomers criticize astrology on absurd grounds, supposing, for instance, that astrologers have no knowledge of astronomy and such phenomena as the precession of the equinoxes, or that they believe that the effects of the planets are connected with gravity.

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Stars and Planets

The simplest explanation that early Man devised in order to explain how the solar system worked was to suppose that Earth stood in the center of a revolving sphere, upon the interior surface of which the stars were somehow stuck, and that the planets moved between those stars and observers on Earth. Although we now know that this, of course, is nonsense, it is a useful concept to remember when studying the movements of the planets: the stars that seem to move around us because of the revolution of the Earth indeed seem to be stationary when they are viewed in relation to each other, and so we can use them as a means of making measurements of planetary movements.

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The Three Circles

Three "great circles" are used by astrologers in order to fix the positions of the planets relative to the Earth. These three circles are the horizon, the equator and ecliptic. When we project the equator on to the imaginary celestial sphere, it becomes the celestial equator (it is, of course, right above the Earth's equator). The celestial equator divides the heavens into two hemispheres, northern and southern, with the celestial poles at the center of each -just as the North and South Poles mark the centre of the Earth's hemispheres.

Two imaginary circles - the equator and the ecliptic - make it possible for us to fix the positions of the planets relative to the Earth. The celestial equator is simply the Earth's equator projected upon the surface of our imaginary sphere: so it stands immediately "above" the Earthly equator, dividing the sky into the northern and southern hemispheres, in the center of which stand the celestial poles, above the Earth's North and South Poles.

The Ecliptic - The ecliptic is another imaginary circle, which is marked out by the Sun as it seems to travel around the Earth. It lies at an angle to the celestial equator, so their paths meet twice - once at the first point of the sign Aries (this is called the Vernal Equinox) and again at the first point of Libra (called the Autumnal Equinox). In northern latitudes, the Sun reaches those two points at the official beginning of spring and fall,- in southern latitudes, the first point of Aries indicates the coming of fall.

Solstices - The highest points of the ecliptic - furthest from the equator - are known as the solstices. The Sun reaches the summer solstice when it enters Cancer, and the winter solstice at the beginning of Capricorn. (Again, the reverse is true in southern latitudes. ) At the point when the Sun reaches either the summer or winter solstice - its furthest distance from the equator, either north or south - it seems to stand still before resuming its journey in the opposite direction. At the June solstice it traces a circle known as the Tropic of Cancer, and in December as the Tropic of Capricorn; the terms do not refer to the zodiac signs, but simply mark the Sun's maximum declination.

Along the ecliptic we measure the 12 equal divisions of 30° that indicate the zodiac signs. The equator (or equinoctial) is divided into 24 parts of 15° each, which we call hours, so one section of 15° of the sky apparently passes over a particular spot every 60 minutes of the day,

The Sun's Motion - Because the Earth circles the Sun once a year, from our vantage point it seems to move around the ecliptic once every 12 months, passing through each sign of the zodiac in turn.

The Meridian - The meridian is an imaginary line running over the surface of the Earth from pole to pole, and passing through any chosen location. The meridian of your place of birth is the imaginary line running through it from north to south.

Declination - The angular distance of a heavenly body either north or south of the celestial equator is measured in degrees of declination - the equivalent of degrees of latitude on Earth.

The MC (Medium Coeli) or Midheaven - The Midheaven is the point at which the ecliptic meets the meridian of the place of birth.

The IC (Imum Coeli) - The IC is the point exactly opposite the Midheaven. When Placidus and other house division systems are employed it forms the cusp of the fourth house as the Midheaven forms the cusp of the tenth. This is not so when the Equal House system is used; it can then fall in any one of a number of houses, as can the Midheaven.

Nonagesimal - The nonagesimal is the point at 90° from the Ascendant. Note that it is not the same as the Midheaven.

The Ascendant - The Ascendant (or Asc. ) is the degree of the sign rising over the eastern horizon at any given moment.

The Descendant - The Descendant is the point opposite the Ascendant. It is always to be found on the cusp of the seventh house, whichever method of house division is used.

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The Astrolabe

The astrolabe is a very ancient astronomical computer for solving problems relating to time and the position of the Sun and stars in the sky. Several types of astrolabes have been made. By far the most popular type is the planispheric astrolabe, on which the celestial sphere is projected onto the plane of the equator. A typical old astrolabe was made of brass and was about 6 inches (15 cm) in diameter, although much larger and smaller ones were made.

Astrolabes are used to show how the sky looks at a specific place at a given time. This is done by drawing the sky on the face of the astrolabe and marking it so positions in the sky are easy to find. To use an astrolabe, you adjust the moveable components to a specific date and time. Once set, the entire sky, both visible and invisible, is represented on the face of the instrument. This allows a great many astronomical problems to be solved in a very visual way. Typical uses of the astrolabe include finding the time during the day or night, finding the time of a celestial event such as sunrise or sunset and as a handy reference of celestial positions. Astrolabes were also one of the basic astronomy education tools in the late Middle Ages. Old instruments were also used for astrological purposes. The typical astrolabe was not a navigational instrument although an instrument called the mariner's astrolabe was widely used. The mariner's astrolabe is simply a ring marked in degrees for measuring celestial altitudes.

The history of the astrolabe begins more than two thousand years ago. The principles of the astrolabe projection were known before 150 B.C., and true astrolabes were made before A.D. 400. The astrolabe was highly developed in the Islamic world by 800 and was introduced to Europe from Islamic Spain (Andalusia) in the early 12th century. It was the most popular astronomical instrument until about 1650, when it was replaced by more specialized and accurate instruments. Astrolabes are still appreciated for their unique capabilites and their value for astronomy education.

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The Zodiac

The zodiac originated as a device for measuring time; no one knows how it first became involved in the classification of personalities or attempts to predict the future, although the first known personal horoscope was drawn up in 410 BC, and the zodiac certainly existed by 500 BC. There is evidence that the "modern" zodiac was in place long before the birth of Christ. When Plato wrote about astrology in 365 BC the signs were still ruled by gods and goddesses and were linked to myths from Babylon, Egypt and Assyria, and much modern astrological interpretation relates very powerfully to myth, since these concepts form a background to human behavior and motivation.

The solar system is rather like a gigantic plate, spinning through space. The planets revolve around the Sun on the same plane as the Earth - Pluto, exceptionally, is at 17° from the Earth's plane, but the rest of the planets are under 7°. This explains the fact that, when we observe them from the Earth, the planets seem to move in a fairly constricted path - the ecliptic. The zodiac signs are all set within this path (in fact, to the 12 signs with which we are familiar, should be added Ophiuchus, the Serpent-bearer, and Cetus, the Whale, but these signs are not considered to be astrologically significant).

The role of the signs It cannot be too strongly emphasized that the constellations or signs are merely a convenience to astrologers. They are simply an easy way of naming the 30° segments of the sky within which the Sun, Moon and planets move (the Sun being the star of greatest significance in astrology). Whilst the symbolic creatures or beings of the zodiac - the Crab, the Archer, the Twins and so on - no doubt played their part in the evolution of the theory, they have no other significance.

Precession of the equinoxes It is important to note that, because of an astronomical phenomenon called the precession of the equinoxes, these 30° divisions no longer coincide with the constellations. Today, the astrological point Aries 0° is to be found in the astronomical constellation of Pisces. However, this does not affect the astrological theory, which is geared to the relevant segments of the sky rather than the constellations which appear in them, and after which they are named.

Signs of long and short ascension Because the Earth's axes are oblique in relation to the ecliptic, some of the constellations; (the astrological "signs") take longer than others to rise over the horizon. In northern latitudes, the signs of long ascension are Cancer, Leo,Virgo, Libra, Scorpio, Sagittarius and Capricorn. The signs of short ascension are Aries, Taurus, Gemini,Aquarius and Pisces. The opposite applies in southern latitudes.

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The Solar System

Five of the planets - Mercury, Venus, Mars, Jupiter, and Saturn - have been known ever since man began looking at the heavens. They immediately drew his attention by their brightness and their movements (the word "planet" comes from the Greek word for "wanderer"). Four planets - Uranus, Neptune, Pluto, and, most recently, Chiron - were discovered after the invention of the telescope. Astrologers were excited to find that their influences filled gaps in interpretations made by ancient astrologers who knew nothing of them.

The Sun - The Sun, at the center of the system of the planets of which the Earth is a member, is about 150 million kilometers (93 million miles) from the Earth and is so large that 109 Earths could be placed side by side inside it.

The Moon - The Moon, the Earth's only natural satellite, is (for convenience) treated as a planet. However, unlike the "real" planets, it circles the Earth (once every 27 days, 7 hours, 43 minutes and 11 seconds), while the Earth and Moon together circle the Sun. Lit by the Sun's light, it appears to grow and decrease in size - wax and wane. It is "new" when it is between the Earth and the Sun, and therefore cannot be seen, and is "full" 141/2 days later, when in full sunlight. Because the Moon moves eastwards against the background of the stars, it rises later each night - on average about 50 minutes later, although sometimes it is only 15 minutes and sometimes as much as an hour later. A full Moon always rises at sunset and sets at sunrise. When the Moon passes precisely in front of the Sun, there is a solar eclipse - this is a dramatic event which the ancients believed to be of great astrological significance. Indeed, much modern research has been done into this phenomenon - with dramatic results.

Mercury - Mercury is the nearest planet to the Sun, and astronomically it is referred to as an "inferior" planet - that is, its orbit lies between those of Earth and the Sun. It is the smallest of the known planets (only 4,880 kilometers, or 3,000 miles in diameter), and has a year of 88 days - that is the time that it takes to travel round the Sun. So, apart from the Moon, it is the fastest-moving of the bodies used by astrologers, and its movements are comparatively eccentric, for its orbit sometimes takes it to within 47 million kilometers (29 million miles) of the Sun, and sometimes whirls it 70 million kilometers (43 million miles) away. As seen from the Earth, however, it is always relatively close to the Sun and never further away than 27°.

Venus - The other "inferior" planet, Venus is 1. 2 million kilometers (67. 2 million miles from the Sun, and takes 225 days to travel round it. Its maximum distance from the Sun as seen from Earth is 48°, so, unlike Mercury, it is usually visible at night.

Mars - Mars is the first planet on the far side of Earth from the Sun, and so is known as a "superior" planet. It has a very eccentric orbit, and can pass as close to the Sun as 208 million kilometers (129 million miles), or be as distant as 228 million kilometers (142 million miles). It circles the Sun once every 687 days.

Jupiter - The largest body in the solar system (143,000 kilometers, or 89,000 miles in diameter), Jupiter is 778 million kilometers (484 million miles) from the Sun and orbits it once every 11.86 years. It has a magnetic field 20,000 times stronger than that of Earth, and sends out radio waves. It has 15 moons; of these, Ganymede, Callisto, Io and Europa are visible from Earth through even a small telescope (they were discovered by Galileo in 1610, with the earliest practical telescope).

Saturn - Saturn is the second largest planet in the solar system (120,000 kilometers, or 74,600 miles in diameter); its orbit around the Sun, from which it is 1,426 million kilometers (886. 7 million miles) distant, takes 291/2 years. Its rings three main ones, but hundreds, perhaps thousands, of others - were first studied in 1655, and are now known to be made of ice and rock, whirling around the planet. Saturn has 19 moons, and maybe more.

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The Modern Planets

The five planets mentioned above were all known in antiquity; the four remaining were discovered in modern times, and are generally referred to "the modern planets" by astrologers.

Uranus - Uranus, accidentally discovered by William Herschel in 1781, is 2,870 million kilometers (1,783 million miles) from the Sun and takes no less than 84 years to travel round it. It is four times the size of Earth, has a system of rings and four satellites.

Neptune - Neptune was discovered in 1846, after studies of the perturbations of the path of Uranus suggested that they must be caused by the existence of an unknown planet. Slightly larger than Uranus, Neptune takes 165 years to travel around the Sun, from which it is 4,497 million kilometers (2,794 million miles) distant. It has two satellites, Triton and Nereid. Triton, which orbits Neptune every six days, is one of the largest moons in the solar system.

Pluto - Percival Lowell assumed that Pluto existed, on the basis of mathematical calculations. Between 3,200 and 4,800 kilometers (2,000 and 3,000 miles) in diameter, it was first seen by Clyde Tombaugh in 1930. The planet's orbit is 17° inclined to the ecliptic, and is some 5,800 million kilometers (3,600 million miles) from the Sun, around which it circles once every 248 years. Its eccentric orbit brings it within that of Neptune, but a collision is thought to be unlikely. Its moon, Charon, was discovered in 1978.

Chiron - Discovered in November 1977, Chiron has an orbit of 50. 7 years, which takes it in towards Saturn and out so it comes within the orb of Uranus. It is between 148 and 208 kilometers (92 and 129 miles) in diameter, and rotates in under six hours.

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The Planets' Movements

The planets do not move in perfect circles around the Sun. While the eccentricity of their orbits is more important to astronomers than it is to astrologers, we must take note of one phenomenon: as we look at them from the Earth, planets may seem to hesitate, stop and then move backwards for a time before resuming their forward motion. A planet that is moving backwards in this way is said to be in retrograde motion, and the optical illusion is the result of the Earth overtaking the planet in question (as when, in a car overtaking another car, you see the overtaken car falling behind, although it is still moving forwards). The point at which a planet goes retrograde is marked in astrological tables with the capital letter "W', and its return to direct motion is marked by a capital "D". Some astrologers vastly overestimate the effects of a retrograde planet.

Astrological conjunctions

A conjunction occurs when two planets or more (remember that to astrologers the Sun is also a planet) are in line, as seen from the Earth. Mercury and venus can be in either superior or inferior conjunction: inferior when they are between the Sun and the Earth, and superior when they are behind the Sun, as seen from the Earth.