Part 6 of An Irish Corpus Astronomiae, being Manus O'Donnell's seventeenth century version of the Lunario of Geronymo Cortès

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An Irish Corpus Astronomiae, being Manus O'Donnell's seventeenth century version of the Lunario of Geronymo Cortès (Author: [unknown])

Chapter 6

THE SIXTH CHAPTER

CONCERNING THE ECLIPSE OF THE SUN AND THE MOON

To complete this work it seemed good to me to treat of eclipses of the sun and moon briefly. Accordingly I say that an eclipse of the sun is when the moon comes between us and the sun, so that the light of the sun leaves us, and this happens at new moon. But be it noted that for an eclipse of the sun two things are required: first, the sun and the moon must be in the same sign; second, both of them must be in one of two points which are called caput et Cauda Draconis, i.e., the head and tail of the Dragon. Accordingly an eclipse of the sun does not take place every time it and the moon happen to be in the same sign, but in addition to that they must both be in one of these two points, and according to the nearness or distance of the eclipse of the sun from those two points is the eclipse great or small. What we call an eclipse of the moon is when the moon travels on the shadow of the earth, which rises high owing to the sun being at the other side underneath, and so its light parts from us, since it is not in sight of the sun, whence it gets its light; and this is called the real eclipse, because the sun and moon are at this time exactly opposite one another, and the centre of the earth directly between them, and so extinction comes on the moou because the light of the siin which gives it light, is separated from it as the earth is straight between them. And for an eclipse of the moon two things are necessary: first, the sun and the moon must be opposite each other; secondly, the sun must be in one of the aforesaid points, and the moon in the other point. And if you wish to find out what is the meaning of

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the head and tail of the Dragon, I say that the astronomers suppose a circulum, i.e., a circle or round ring in the sky of 12 degrees in width, which is called Zodiacum, as we have said on page 123, and on the midst of this moves the sun with its natural motion, and the path on which the sun travels is called Eclyptica. And be it noted that the moon does not pass out beyond this width of the Zodiacum at all according to its own natural motion; nevertheless it travels sometimes on part of that path of the sun which is called Eclyptica, and at other times on the other part of it. And when the moon goes from north to south it goes on the Eclyptica, or as it is better to say, it goes on the line on which the sun travels; and that point on which the moon travels from one side of the line to the other side of it at that time they call Cauda Draconis, or the tail of the Dragon, and when the moon turns back from the South to the North it goes on the same line, and that point they call Caput Draconis, or the head of the Dragon.

TO KNOW THE THINGS WHICH THE ECLIPSES CAUSE

Illustration is given here of the method in which it is known what things these eclipses work and cause; so that it is not necessary for one to be an astronomer to find them out. Accordingly there is nothing to be done but to look what is the house or sign in which the sun is, if it is it that is to be eclipsed, or in which the moon will be, if it is it that is to be eclipsed, and he will know the things we have said: for if it is in the sign or house of Mars the sun will be, or the moon which is to be eclipsed, it is certain (according to Ptolemy Lib. 2, cap. 7), that it will work according to the nature of Mars, which is as we mentioned about it on page.

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73. And if it is in a sign which is the house of another planet that it is, it will work according to the nature of that planet, which is declarcd in their own treatises, and be it noted that the twelve signs are the houses of the planets as we have said.

CONCERNING THE TIME AT WHICH THE EFFECT OF THE ECLIPSES BEGINS

The only difficulty here is to know accurately the hour of day or night in which the eclipse begins, and further, the length of the day from sunrise to sunset (which is called the working day), and in that way will be found the correct time when the effect of the eclipse begins, and the length of time it will last; and in order that this may be more intelligible, I suppose that the eclipse came on the sun at the end of two hours after it rose, and that the length of that day is twelve hours, i.e., from sunrise to sunset. I say, then, that the effect of this eclipse will begin at the end of two months after that, because, since two hours are the sixth part of that day, the sixth part of a year is two months. And in case that the length of the day is ten hours, the effect of the eclipse will begin at the end of two months and 12 days, for that is the fifth part of the year, as two hours is the fifth part of the working day. And in case that the length of the day is 14 hours, the eclipse will begin to have effect at the end of the seventh part of the year, i. e., at the end of a month and 21 days, for that (i.e., two hours) is the seventh part of that day; and so, according to that principle, every other hour will be understood, whether the day be short or long, bearing in mind further that it is in the same way that the eclipse of the moon is understood. And in order that you may understand how long the effect of the eclipses lasts, notice that

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for every hour the eclipse lasts on the sun itself, the effect of the eclipse of the sun lasts a year, and that the effect of an eclipse of the moon lasts a month for every hour the eclipse lasts on the moon itself.

THE METHOD BY WHICH MAY BE KNOWN THE PLACES IN THE WORLD IN WHICH THE EFFECT OF THE ECLIPSES WILL BE FELT

That this may be shown, one must look in what sign the planet, be it sun or moon, will be which is to be eclipsed, and in the provinces over which that sign rules the eclipse will have effect. Information will be found of the sign in which the sun will be every day, and of the provinces and the cities over which each sign rules, in the place where we treated of the signs themselves; and information will be found of the sign in which the moon will be every day in the place where we treated of the moon itself, and of the other planets. And take heed that an eclipse of the sun usually takes place at the new moon, and that the time when an eclipse of the moon takes place is when itself is complete or full.

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