Darkening of the light by David Plant
David Plant

Darkening of the Light

Essential introduction to understanding eclipses


Of all the celestial events visible from the Earth, eclipses are the most awesome. The term is derived from the Greek word ekleipsis, meaning ‘abandonment’ or ‘failure’. During a solar eclipse, light from the Sun is visibly diminished, sometimes to the extent that it disappears altogether. Regions of the world directly affected by the eclipse are plunged into an eerie half-light. During a lunar eclipse, a coppery-red shadow moves across the bright face of the full moon, sometimes obscuring it completely so that the Moon glows with a dim, reddish light.

Diagram to show the excliptic, by Deb Houlding Eclipses result from the astronomical relationship between Earth, Moon and Sun. Since the 16th century it has been firmly established that the Earth is a planet of the solar system in orbit around the central Sun, but our earthbound senses are unable to perceive its motion. Seen from Earth, it is the Sun that appears to move. It travels across the sky each day from east to west and traces out a regular path amongst the background stars as it makes its annual journey through the 12 signs of the zodiac. The Sun’s path is called the ecliptic because it is that part of the sky that eclipses occur.

The Moon is in orbit around the Earth and is described astronomically as Earth’s natural satellite. It travels through the 12 signs of the zodiac in one month, during which it completes its cycle of phases from New Moon to Full Moon and back. The phases are a result of the varying angles from which we see the bright side of the Moon at different stages of its monthly orbit. The Moon’s motion along the ecliptic is measured in degrees and minutes of celestial longitude, but its orbit does not align exactly with the ecliptic. It deviates by about 5° of celestial latitude north and south each month. Every two weeks, the Moon crosses the Sun’s track at the points known as the Moon’s nodes. If the Sun is close to one of the nodes when the Moon crosses the ecliptic, an eclipse is imminent.

A solar eclipse occurs at the New Moon, when the Moon lines up between the Earth and the Sun at one of the nodes. The Moon is much smaller than the Sun, yet from Earth it appears to be almost exactly the same size because it is so much closer. During a solar eclipse the Moon moves across the Sun, blocking its light and casting a shadow onto the Earth. At a partial solar eclipse Sun’s light is partly obscured; at a total solar eclipse it is completely blotted out. The Moon’s distance from Earth varies by about 2700 miles over the course of a lunar cycle. A third type of solar eclipse occurs when the Moon aligns with the Sun at its greatest distance from Earth (apogee). It moves across the Sun as in a total eclipse but is too small to cover it entirely. A ring of sunlight remains visible at mid-eclipse. This is called an annular eclipse (Latin: annulus, ‘ring’).

Solar eclipse A total solar eclipse is a rare sight. The Moon’s shadow, or umbra, moves across a relatively narrow area of the Earth’s surface in an eclipse track, and only those regions within the track experience a total eclipse. The last one visible from the British Isles was on 11th August 1999, when the track crossed Cornwall; the next will be on 23rd September 2090. A partial eclipse affects a wider area, but the Sun is so bright that no obvious darkening occurs until it is almost completely obscured, so a partial eclipse can easily pass unnoticed.

A lunar eclipse occurs at the Full Moon, when the Moon crosses the ecliptic in opposition to the Sun. With the Sun and Moon aligned on either side of the Earth, the Moon passes through the shadow projected by the Earth into space. The shadow can be seen creeping across the lunar disc as the eclipse proceeds. In a total lunar eclipse, the Moon is completely engulfed in the Earth’s main umbra and no sunlight reaches its surface. In a partial lunar eclipse, it partly enters the umbra and only part of its surface is darkened. A penumbral eclipse, sometimes called an appulse, occurs when the Moon misses the Earth’s umbra but passes through its penumbra or secondary shadow. This results in a slight darkening of the Moon’s disc which is far less dramatic than the reddening of a total lunar eclipse.

lunar eclipse Astronomers will travel thousands of miles to observe a total eclipse of the Sun because each one is visible from such a small area of the Earth’s surface. Lunar eclipses are easier to observe. There is no eclipse track. A lunar eclipse is visible from anywhere on Earth where the Moon is above the horizon.

The Moon’s Nodes
Click for details of how this dragon volvelle was used Because of their connection with eclipses, the Moon’s nodes are significant astrological points in their own right. Traditionally, the north node (north node) is called the 'Dragon’s Head’ (Caput Draconis). It is said to be a benefic influence of the nature of Jupiter. The south node (south node) is called the 'Dragon’s Tail’ (Cauda Draconis) and is malefic, of the nature of Saturn. Eclipses are often linked with dragon symbolism; in old star maps a celestial dragon was depicted curled around the pole of the ecliptic, forming the constellation Draco.

The nodes themselves travel retrograde along the ecliptic. Each month the Moon crosses the ecliptic roughly 1½° west of its previous crossing point, so the nodal line , which joins the north and south nodes, regresses about 19° every year and makes a complete retrograde revolution of the ecliptic in just under 19 years. Twice each year, the Sun moves into conjunction with one of the nodes. The period of about 40 days around the conjunction is called an eclipse season, during which any new or full moon is likely to be an eclipse.
Ecliptic Limits
For any type of solar eclipse to take place, the Moon’s latitude must not exceed 1°28' N or S. When a New Moon occurs within 18°31' longitude of either of the nodes, a partial solar eclipse is possible if the Moon’s latitude is small enough. Within 15°21' of a node, a solar eclipse of some kind must occur. A total or annular eclipse occurs when the Moon’s latitude is within 58' N or S and a new moon falls within 9°55' longitude of a node.

For any type of lunar eclipse to take place the Moon’s latitude must not exceed 56' N or S and a Full mMon must occur within 11°38' of the nodal line. For a total lunar eclipse, the Moon’s latitude must not exceed 26' N or S and the Full Moon must fall within 3°45' of the nodal line.

Eclipse facts

- A lunar eclipse lasts about 6 hours from beginning to end. The period of totality is around 1½ hours and is visible over the whole of the nocturnal hemisphere.

- The focal point of a solar eclipse covers an area no more than 170 miles in diameter, though the eclipse track may be thousands of miles long. The eclipse lasts up to 7½ minutes.

- During a lunar eclipse the temperature of the Moon drops 100° per hour.

- Areas affected by a solar eclipse experience a dramatic drop in electromagnetic energy. The atmosphere is turned into a negatively charged environment; there is a measurable reduction in the surface tension of moisture and the properties of protein - the basis of all life - is known to experience change.
graphic embellishment

About the author: David Plant

This article was first published in the Traditional Astrologer magazine, 1994.



(Click the eclipse images to enlarge the charts):

Timing the effect of eclipses
A number of attempts have been made to determine how long the ‘effects’ of eclipses endure. It is suggested that these inquiries are erroneously conceived. To reason by analogy: how long do the effects of a blow last? Clearly two factors are involved - the violence of the impact and the susceptibility of the object struck. A blow by a hand on a stone has no effect on the stone; a blow by a knife on soft flesh may inflict a lifelong injury. Thus, we must consider how ‘violently’ an eclipse affects the figure under consideration, and that must depend upon how closely it falls to sensitive points therein; and we must further consider how susceptible, or sensitive, that spot is. If the eclipse does not fall nearer than, say, 5° of any important body or point the ‘effect’ will be negligible, even at the time, and certainly will have no duration. But if it falls on the very degree held by a body and if, in addition, that body is highly sensitive owing to its radical condition, the so-called effects may be serious and long lasting.

Charles CarterNevertheless it is true that an eclipse may produce little or nothing at the time but may apparently correspond to something important but occurring some considerable time later. The most usual times seem to be when the Sun comes to the next square of the place of the eclipse, i.e., three months later, or when a planet, particularly Mars, transits the place of the eclipse.
Extracted from An Introduction to Political Astrology
(a.k.a. 'Mundane Astrology'), by Charles Carter, 1951, p.54.
(Republished, 2005 by Astrology Classics | preview).

article by David Plant

Interpreting the Eclipses Mundane Astrology
Books on eclipses (for astrologers)
Interpreting the Eclipses - Robert Carl Jansky
Mundane Astrology - C. C. Zain
The Predictive Power of Eclipse Paths - Bill Meridian
The Eagle and the Lark - Bernadette Brady

Recommended websites
Time & Date: Eclipses - invaluable resource for detailed information on eclipse paths
Sky & Telescope: Eclipses - eclipse facts & information on upcoming eclipses
NASA: Eclipses - eclipse facts & eclipse info & news
Skyscript Pinterest - eclipse imagery & information on upcoming eclipses

See also:
Asteroids & Comets - David McCann
A Basic Guide to Astro-Meteorology - Kim Farnell
An Introduction to Astro*Carto*Graphy - Martin Davis
Mundane Matters: The National Chart - Claire Chandler
Ingresses: An Introduction to Mundane Astrology - compiled by D. Houlding
Attention all Shipping! (feature on shipping charts) - compiled by D. Houlding
A Guide to Interpreting the Great American Eclipse - by Wade Caves

The Predictive Power of Eclipse Paths The Eagle and the Lark

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David Plant is a scholar of the history and traditional practice of astrology, who served as co-editor of the Traditional Astrologer magazine (1993-2000) where this article first appeared. David is also well known for his expertise on the English Civil War period and the life and work of the 17th century astrologer William Lilly, and for being the creator of the excellent resources avilable at the British Civil Wars Project (http://bcw-project.org), which explores the turmoil of the Civil Wars and Interregnum, and the constitutional experiments of the Commonwealth and Protectorate period of the 1650s.