The Discovery of a World in the Moone/Chapter 6

by John Wilkins

Proposition 5.

That the Moone hath not any light of her owne.

TWas the fancy of some of the Jewes, and more especially of Rabbi Simeon, that the Moone was nothing else but a contracted Sunne, ^[1] and that both those planets at their first creation were equall both in light and quantity, for because God did then call them both great lights, therefore they inferred, that they must be both equall in bignesse. But a while after (as the tradition goes) the ambitious Moone put up her complaint to God against the Sunne, shewing, that it was not fit there should be two such great lights in the heavens, a Monarchy would best become the place of order and harmony. Upon this God commanded her to contract her selfe into a narrower compasse, but she being much discontented hereat, replies, What! because I have spoken that which is reason and equity, must I therefore be diminished? This sentence could not chuse but much trouble her; and for this reason was shee in much distresse and griefe for a long space, but that her sorrow might be some way pacified, God bid her be of good cheere, because her priviledges and charet should be greater then the Suns, he should appeare in the day time onely, shee both in the day and night, but her melancholy being not satisfied with this, shee replyed againe, that that alas was no benefit, for in the day-time she should be either not seene, or not noted. Wherefore, God to comfort her up, promised, that his people the Israelites should celebrate all their feasts and holy daies by a computation of her moneths, but this being not able to content her, shee has looked very melancholy ever since; however shee hath still reserved much light of her owne.

Others there were, that did thinke the Moone to be a round globe, the one halfe of whole body was of a bright substance, the other halfe being darke, and the divers conversions of those sides towards our eyes, caused the variety of her appearances: of this opinion was Berosus, as he is cited by Vitruvius,^[2] and St. Austin thought it was probable enough, but this fancy is almost equally absurd with the former, and both of them sound rather like fables, then philosophicall truths. You may commonly see how this latter does contradict frequent and easie experience, for 'tis observed, that that spot which is perceived about her middle, when she is in the increase, may be discern'd in the same place when she is in the ful: whence it must follow, that the same part which was before darkened, is after inlightened, and that the one part is not alwaies darke, and the other light of it selfe, but enough of this, I would be loth to make an enemy, that I may afterwards overcome him, or bestow time in proving that which is already granted. I suppose now, that neither of them hath any patrons, and therefore need no confutation.

’Tis agreed upon by all sides, that this Planet receives most of her light from the Sunne, but the chiefe controversie is, whether or no she hath any of her owne? The greater multitude affirme this. Cardan amongst the rest, is very confident of it, and he thinkes that if any of us were in the Moone at the time of her greatest eclipse,^[3] Lunam aspiceremus non secus ac innumeris cereis splendidissimis accensis, atque in eas oculis defixis cæcutiremus; “wee should perceive so great a brightnesse of her owne, that would blind us with the meere sight,” and when shee is enlightened by the Sunne, then no eagles eye if there were any there, is able to looke upon her. This Cardan saies, and hee doth but say it without bringing any proofe for its confirmation. However, I will set downe the arguments that are usually urged for this opinion, and they are taken either from Scripture or reason; from Scripture is urged that place, 1 Cor. 15. where it is said, There is one glory of the Sunne, and another glory of the Moone. Vlysses Albergettus urges, that in Math. 24. 22. ἡ σελήνη οὐ δώσει τὸ φέγγος αὐτῆς, The Moone shall not give her light: therefore (saies he) she hath some of her owne.

But to these wee may easily answer that the glory and light there spoken of, may be said to be hers, though it be derived, as you may see in many other instances.

The arguments from reason are taken either

1. From that light which is discerned in her, when there is a totall eclipse of her owne body, or of the Sunne.

2. For the light which is discerned in the darker part of her body, when she is but a little distant from the Sunne.

1. For when there are any totall eclipses, there appeares in her body a great rednesse, and many times light enough to cause a remarkeable shade, as common experience doth sufficiently manifest: but this cannot come from the Sunne, since at such times either the earth, or her owne body shades her from the Sun-beames, therefore it must proceede from her owne light.

2. Two or three daies after the new Moone, wee may perceive light in her whole body, whereas the rayes of the Sun reflect but upon a small part of that which is visible, therefore 'tis likely that there is some light of her owne.

In answering to these objections, I shall first shew, that this light cannot be her owne, and then declare that which is the true reason of it.

That it is not her own, appeares

1. From the variety of it at divers times; for ’tis commonly observed, that sometimes ’tis of a brighter, sometimes of a darker appearance, now redder, and at another time of a more duskish colour. The observation of this variety in divers eclipses, you may see set downe by Keplar^[4] and many others, but now this could not be if that light were her owne, that being constantly the same, and without any reason of such an alteration: So that thus I may argue.

If there were any light proper to the Moone, then would that Planet appeare brightest when she is eclipsed in her Perige, being neerest to the earth, and so consequently more obscure and duskish when she is in her Apoge or farthest from it; the reason is, because the neerer any enlightened body comes to the sight, by so much the more strong are the species and the better perceived. This sequell is granted by some of our adversaries, and they are the very words of noble Tycho,^[5] Si luna genuino gauderet lumine, utique cum in umbra terræ esset, illud non amitteret, sed eò evidentiùs exereret, omne enim lumen in tenebris, plus splendet cum alio majore fulgere no præpeditur. If the Moone had any light of her owne, then would she not lose it in the earths shadow, but rather shine more clearely, since every light appeares greater in the darke, when it is not hindered by a more perspicuous brightnesse.

But now the event falls out cleane contrary, (as observation doth manifest, and our opposites themselves doe grant)^[6] the Moone appearing with a more reddish and cleare light when she is eclipsed being in her Apoge or farthest distance, and a more blackish yron colour when she is in her Perige or neerest to us, therefore shee hath not any light of her owne. Nor may we thinke that the earths shadow can cloud the proper light of the Moone from appearing, or take away any thing from her inherent brightnesse, for this were to thinke a shadow to be a body, an opinion altogether mis-becomming a Philosopher, as Tycho grants in the fore-cited place, Nec umbra terræ corporeum quid est, aut densa aliqua substantia, aut lunæ lumen obtenebrare possit, atque id visui nostro præripere, sed est quædam privatio luminis solaris, ob interpositum opacum corpus terræ. Nor is the earths shadow any corporall thing, or thicke substance, that it can cloud the Moones brightnesse, or take it away from our sight, but it is a meere privation of the Suns light, by reason of the interposition of the earths opacous body.

2. If shee had any light of her owne then that would in it selfe be, either such a ruddy brightnesse as appeares in the eclipses, or else such a leaden duskish light as wee see in the darker parts of her body, when shee is a little past the conjunction. (That it must be one of these may follow from the opposite arguments) but it is neither of these, therefore she hath none of her owne.

1. ’Tis not such a ruddy light as appeares in eclipses, for then why can wee not see the like rednesse, when wee may discerne the obscurer parts of the Moone?

You will say, perhaps, that then the neerenesse of that greater light, takes away that appearance.

I reply, this cannot be, for then why does Mars shine with his wonted rednesse, when he is neere the Moone? or why cannot her greater brightnesse make him appeare white as the other Planets? nor can there be any reason given why that greater light should represent her body under a false colour.

2. 'Tis not such a duskish leaden light, as we see in the darker part of her body, when shee is about a sextile Asp & distant from the Sunne, for then why does shee appeare red in the eclipses, since the more shade cannot choose such variety, for 'tis the nature of darknessee by its opposition, rather to make things appeare of a more white and clear brightnesse then they are in themselves, or if it be the shade, yet those parts of the Moone are then in the shade of her body, and therefore in reason should have the like rednesse. Since then neither of these lights are hers, it followes that she hath none of her owne. Nor is this a singular opinion, but it hath had many learned patrons, such was Macrobius^[7], who being for this quoted of Rhodiginus, he calls him vir reconditissimæ scientiæ^[8], a man who knew more than ordinary Philosophers, thus commending the opinion in the credit of the Authour. To him assents the Venerable Bede, upon whom the glosse hath this comparison.^[9] As the Looking-glasse represents not any image within it selfe, unlesse it receive some from without; so the Moone hath not any light, but what is bestowed by the Sun. To these agreed Albertus Magnus, Scaliger, Mæslin, and more especially Mulapertius, ^[10] whose words are more pat to the purpose then others, and therefore I shall set them downe as you may finde them in his Preface to his Treatise concerning the Austriaca sydera; Luna, Venus, & Mercurius, terrestris & humidæ sunt substantiæ ideoque de suo non lucere, sicut nec terra. The Moone, Venus, and Mercurie (saith he) are of an earthly and moyst substance, and therefore have no more light of their owne, then the earth hath. Nay, some there are who thinke that all the other Starres doe receive that light, whereby they appeare visible to us from the Sunne, so Ptolomie, Isidore Hispalensis, Albertus Magnus and Bede, much more then must the Moone shine with a borrowed light. ^[11][12][13]

But enough of this. I have now sufficiently shewed what at the first I promised, that this light is not proper to the Moone. It remaines in the next place, that I tell you the true reason of it. And here, I thinke 'tis probable that the light which appeares in the Moone at the eclipses is nothing else but the second species of the Sunnes rayes which passe through the shadow unto her body: and from a mixture of this second light with the shadow, arises that rednesse which at such times appeares unto us. I may call it Lumen crepusculum, the Aurora of the Moone, or such a kinde of blushing light, that the Sunne causes when he is neere his rising, when he bestowes some small light upon the thicker vapours. Thus wee see commonly the Sunne being in the Horizon, and the reflexion growing weake, how his beames make the waters appeare very red.

The Moabites in Iehorams time when they rose early in the morning, and beheld the waters a farre off, mistooke them for blood. ^[14] Et causa hujus est, quia radius solaris in aurora contrahit quandam rubedinem, propter vapores combustos manentes circa superficiem terræ, per quos radii transeunt, & ideo cum repercutiantur in aqua ad oculos nostros, trahunt secum eundem ruborem, & faciunt apparere locum aquarum, in quo est repercussio esse rubrum, saith Tostatus.^[15] The reason is, because of his rayes, which being in the lower vapours, those doe convey an imperfect mixed light upon the waters. Thus the Moone being in the earths shadow, and the Sunne beames which are round about it, not being able to come directly unto her body, yet some second raies there are, which passing through the shadow, make her appeare in that ruddy colour: So that she must appear brightest, when shee is eclipsed, being in her Apoge, or greatest distance from us, because then the cone of the earths shadow is lesse, and the refraction is made through a narrower medium. So on the contrary, she must be represented under a more darke and obscure forme when she is eclipsed, being in her Perige, or neerest to the earth, because then she is involved in a greater shadow, or bigger part of the cone, and so the refraction passing through a greater medium, the light must needes be weaker which doth proceed from it. If you aske now what the reason may be of that light which we discerne in the darker part of the new Moone: I answer, 'tis reflected from our earth which returnes as great a brightnesse to that Planet, as it receives from it. This I shall have occasion to prove afterward,

I have now done with these propositions which were set downe to cleare the passage, and confirme the suppositions implied in the opinion, I shall in the next place proceed to a more direct treating of the chief matter in hand.

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1. Tostatus in 1. Gen. Hieron. de 5. Hide. Hebræoma l. 2. c. 4.
2. Lib. 9. Architecturæ. in enarrat. Psalmorum.
3. De Subtil. lib. 3.
4. Opt. Astron. c. 7. num. 3.
5. De nova stella lib. 1. c. 10.
6. Reinhold comment. in Purb. Theor. pag. 164.
7. Somn. Scip. l. 1. c. 20.
8. Lect. antiq. l. 1. c. 15.
9. In lib. de natur. rerum.
10. De 4r. Coævis. Q. 4ª. Art. 21. Exercit. 62. 1. Epitome. Astron. lib. 4. p. 2.
11. Originum l. 3. c. 60.
12. De Cœlo. l. 2.
13. De ratione tempor. c. 4.
14. 2 King. 3. 22.
15. 2ª. Quæst. in hoc cap.