# Astronomical Dialogues Between a Gentleman and a Lady/Dialogue 3

​The next day my Affairs called me away, for some Time; but at my Return, as I found the Telescopes and other Instruments, I had sent for, in perfect good Order, so I found the Lady had been close at her Astronomical Studies: She was exactly ready in all Problems upon either Globe, and had gotten such an intimate Knowledge of the Stars, that she had also acquired a very tolerable Knowledge in the several Systems of the Universe, or Hypotheses to solve the Celestial Appearances, as they are called by ​Astronomers; and long'd with great Impatience to see the Use of the Telescopes and Quadrants, &c. which I had sent down to her Country-Seat.
Where soon after I arrived, she put me upon beginning our Observations, and had methodized the Enquiries and Questions she designed to make, with great Address and Dexterity.
Let us begin, said she, to talk a little about the Sun.Sun: I think you agree, that his Centre appears to move always in the same Line, or in the Ecliptick; but I think you say his apparent Motion is unequal there.
'Tis true, said I, Madam, for when the Earth is nearest the Sun, as she is in Winter, then she, in reality, and the Sun, seemingly, moves faster than in the Summer, when the Distance between the Earth and the Sun is greater; and accordingly the Sun's Diameter appears bigger in Winter than in Summer.
But, Sir, 'tis strange, methinks, said she, that the Sun's nearer Approach to us in Winter than in Summer, doth not counterchange those Seasons: Have not ​we the greatest Heat from the Sun when we are nearest to him?
No, Madam, said I, for the different Heat of our Seasons of the Year, do not depend upon that, but upon the Sun's Rays falling more directly, or more obliquely upon us; for in the Distance of 70,000,000 of Miles, a little Approach of the Earth to, or its Recess from the Sun, will make no sensible Alteration as to Heat or Cold. But there is another thing arising from this Inequality in the Earth's Motion round the Sun, which is pretty considerable, and that is, that the Sun will appear to tarry about 8 Days longer in the Northern Part of the Ecliptick than he doth in the Southern; the Reason of which is, from the figure of the Earth's oval or elliptick Orbit: [See Lexic. Techn. Vol. II. under Sun.] And thus having given you some general Ideas of these things, I wait your further Commands.
Why, then, said the Lady, pray give me now, for it seems to be a proper Place, some little knowledge about the Equation of Time, which I have read a good deal about, and Tables of which I have seen hanging by Clocks, and put upon Dials ​and Watches; Pray, can our Sun be in the wrong, don't he measure Time equally?
Madam, said I, the daily Revolutions of the Earth's Equator round its Axis, are exactly equal in Time to one another; and yet the Time from the apparent Noon of one Day to that of the next, is unequal, and sometimes greater and sometimes lesser.
Well, said she, I'm glad however, 'tis not our Earth's Fault, and that she is so regular in her diurnal Whirls: But, pray, let me then know, where the Error, or Inequality, lies?
There is, said I, Madam, a double Cause of this Inequality; the former is, that the Earth's Annual Orbit is not an Exact Circle; and the other is, that the Earth's Equator, about which the Diurnal Motion is made, and the Ecliptick, or the Circle she describes round the Sun, are not co-incident, or in one and the same Plane, but make an Angle, as you know they do, at their intersection, of 23° 30′ of which when your Curiosity, and further Knowledge of these Affairs, leads you to make more full Enquiries, you ​will receive a plain and satisfactory Account, from Mr. Whiston's Astronomy, p. 116, 117, &c.
I Thank you, Sir, said she, but, pray, let us now get all things ready to look on the Sun, with your Glasses, that I may know, by my Eyes, as much as I can of that wonderful Luminary, the great Centre of all the Planets Motions.
Our Telescope was about 14 Foot long, and had a plain Glass, smoaked with a Candle, screw'd on before the Eye-Glass, to defend the Eye from receiving any Injury from the too intense Light of the Sun.
After she had looked upon him 2 or 3 times; It appears plainly, said she, to be a great Globe of Fire, or rather, as Butler saith,
and so no doubt it must be, by the great and constant Heat which it gives: But, pray, tell me, as fully as you can, what the late Astronomers and Philosophers ​have discover'd about this vast World of Light. I perceive you suppose him fixt and immoveable, as to Place, in the Centre of what you call the Solar System; but doth he turn round his own Axis or not? how much bigger is he than our Earth? how far is he from us? and how can his Heat continue so long as it hath done, without any sensible Wast or Diminution?
Solar Spots.Madam, said I, by observing carefully the Spots, which often appear in the Sun's Face, tho' there happen to be none now, they have discovered, that the Sun revolves round its own Axis, in about 25 Days.
Spots! said she, What, are there Spots in the Sun, which sometimes appear there, and sometimes not; for God's sake what are those Spots?
There are various Opinions about them, Madam, said I, but the most probable one, is, that they are a kind of Dross or Scum which sometimes gathers upon his Face, as is the Case of melted Metals; for I have seen several Spots, which for a Time appeared distinct, at last some of them quite vanish'd, and ​others run together into one,and so composed a much greater Spot, as was the Case at the Time of the last famous Eclipse of the Sun; and some of these Spots must be immensely large, to appear so big as they do, sometimes, to us, considering the prodigious Distance of the Sun.Distance of the Sun, which probably amounts to about 70 or 80 Millions of Miles.
Eighty Millions of Miles! said she, Why you fright me, my Head turns round, and I'm giddy with the very Notion of it!
And yet, Madam, said I, as great as this Distance is, a Ray of Light runs it in about 7 or 8 Minutes Time; while such a swift Traveller, as a Cannon-Ball, supposing it to move all the Way as fast as when it just parts from the Gun, can't arrive there in 25 Years. These things must needs appear wonderful and surprising to you, but we have very good Reasons to conclude that they are very near to Truth; which I forbear to mention, because perhaps at present, you may not be qualified fully to comprehend them.
Yes, Madam, said I, according to these Ways of Computation, the Sun's Diameter, or his Breadth from one Side to the other, is about 800,000 Miles, which is above 100,000 times greater than the Diameter of our Earth; and therefore his Bulk, or rather the Quantity of Matter in the Sun, must exceed that of the Earth above 10,000,000 times.
And this Consideration of the Vastness of the Sun's Magnitude will account for the Query you rightly enough started, how he can so long continue his Heat without any sensible Diminution? Sir Isaac Newton's Opticks, p.318. last Edition.For we take the Sun and the fix'd Stars to be only very great Bodies of Earth, vehemently hot, whose Heat is preserved by their Greatness, and by the mutual Action and Re-action between them and ​the Light which they emit, and whose Parts are kept from burning out and fuming away, not only by their being of a fix'd Nature; but also by the Weight and Thickness of the Atmospheres which are round about them, and which do strongly compress them, and condense the Vapours and Exhalations which would otherwise fly away from them; but are now by this Means made to fall back again upon his Body; and as to the daily Expence of his Light and Heat, the Particles of Light are so infinitely fall, that out of a Body so big as the Sun, they may be sent for many hundred thousands of Years together, without any sensible lessening of his Bulk, Weight, or Magnitude.
I Believe, I comprehend the Main of your Reasoning, said she, but I am got a little out of my Depth; let me recover firm Ground again, and then I would ask you farther, whether, since you take the Sun to be an immense Globe of Earth, thus set on Fire, and the Fix'd Stars so many Suns.fix'd Stars to be Suns, or Bodies of the same Nature, you don't think the Stars, severally, to have the same Use, and to be the Centres each of them, of Systems of Planets revolving round them, as ours do ​the Sun, to whom they afford such all-chearing Light, and enlivening Heat, as our Sun doth to us? For methinks 'tis a mean Use of them, and below the Wisdom of our Great Creator, to place them in the Sky only to twinkle and divert us; whereas, all of them put together, don't afford us the 10th Part of the Light of the Moon; but if we suppose them all to be Suns to some other Systems of Planets, because of their vast Magnitudes, and because of their shining, as I think you agree they do, by their own Light, and not with one borrowed, like that of the Planets; what a glorious Idea doth it give us of the Almighty Power! of the Wisdom and Goodness of the Divine Nature? And what a poor contemptible Opinion ought it to make us entertain of our selves, who perhaps may bear as little a Proportion in Wisdom and Knowledge, to some of the Beings that inhabit the Starry Regions, as we do in Magnitude to them all; for I can easily conceive infinite Degrees of Knowledge and Perfection, with as great a Variety, that may be in a Series in Creatures between us and the Deity; and perhaps there may be also a considerable one below us.
Ay, said she, such of them as imagine all things made for the sake of Man only; but I have no such lofty Notions of the Dignity of our Species; and I think Mr. Oldham's is a very just Satyr upon that narrow Notion, when, with regard to the very Point before us, he saith, that Man believes,
That Turnspit Angels tread the Spheres for him.
But now I'm talking about the Stars, pray tell me once for all, have these Stars and the Planets no real Influence upon us Mortals?
Not at all, Madam, said I, so as by any Physical Power to Influence our Wills, Lives, and Actions; that kind of Effect is certainly more true with regard to what the Stars have often been unequally compared, the Eyes of a fine Lady of good Sense and Virtue, for Those do certainly, like the Eyes of a good Ma​gistrate, scatter and disperse all Evil before them: They heighten our Genius, and inspire us with Wit, and yet keep our Conversation as chast and modest as they make it entertaining and instructive.
I Always take your Compliments for Instructions, said she, and have no Excuse to make for the Vanity of being pleased with them, but that I will endeavour to be as good as you represent us, and we shall have a much better Reason than ever to value the Power we may have over your Sex, if we can make it help us to reform it: But you will not allow me then to believe any Astrologic Influences?
Not any at all, said I, Madam, for they serve only to nurse Superstition, to fill us with false Fears, deceive us with vain Hopes, and to excite a dangerous Curiosity, and an unreasonable Inquisitiveness into Futurities; and it is indeed, in effect, either making the Stars so many Deities, and consequently running into some of the worst Sorts of the Idolatry of the Heathens; or else 'tis introducing the Notions of a Physical Fatality, and banishing out of our Minds all Religious and Moral Notions.
As I think Milton expresses it; and give me leave to ask you a few Questions about his Brethren, the Stars. Fix'd Stars.If the Sun and they be nearly of the same Bigness, as they appear to be of the same Nature, what an infinite Distance must they be from us?
'Tis very justly observed, Madam, said I; for indeed, whatever their Bigness be (and much less than the Sun we have no reason to suppose any one of them to be) their Their immense Distance.Distance is so great, that the Diameter of the Earth's yearly Orbit or Circle round the Sun, which you know must be double to his Distance from us, and therefore about 160 Millions of Miles: This I say, according to all the ​Observations we can make, and the Reasoning we can form, bears no manner of Proportion, and is but a Point, in comparison of the Distance of the nearest fixed Star; for we have no Reason to suppose them all equally remote from us. And could we advance towards these Stars 99 Parts in a 100 of the whole Distance, and that there were but one hundredth Part of the present Distance remaining, they would appear very little larger to us than they do now. The Distance of Syrius or the Dog-Star, Mr. Huygens takes to be about 27000 times as far from us as the Sun is; so that I believe we are not much out of our Computation, when we conclude, that a Ray of Light cannot come from thence in less than 6 Months time, nor the Cannon-Ball, above-mentioned, in 50000 Years.
Good God! cry'd she, how immense and wonderful are the Works of thy Hands! Why then, said she, if all the Stars were to be extinct or annihilated this next Night, we should not miss them till about 6 Months after!
No, Madam, said I, that Stream of Light now flowing from them to our ​Eyes, should the Fountain be stopped, would be half a Year before it would be run quite out; tho' it run after the rate of above 10 Millions of Miles in a Minute; a Motion almost as quick as Thought itself, as we usually say.
Vid. Accompt. of S. S. Prophecies, p. 288.Well, said she, this hath made an extravagant Notion of Mr. Whiston's about the Distance of Heaven, or the Region appointed for the Bodies of the Blessed, its not being by any means so far off as the supposed Empiræan Heaven of the Divines, much easier to me than it at first appeared; and which then I thought a very new, wild, and unaccountable Opinion. But, pray, lets go on; Is not the Number of these fix'd Stars as wonderful as their Distance?
Yes, in Truth is it, Madam, said I; for as the naked Eye discovers immense Numbers of them in a clear Night, (above 1000 of which are distinguished and taken notice of) and many more in the Northern cold Countries than we can do here; so when assisted by a Telescope of any great Length, it sees amazing Crowds of other Stars, which because they are invisible without these Helps, the Astronomers have called very properly Tele​Telescopic Stars.scopical Stars. Such a Glass as this which we but now used to observe the Sun with, will discover to you many Thousands of Stars, before invisible to the naked Eye; and I think I have told above 70 within that little Bunch of Stars, which we call the Pleiades, or the 7 Stars; tho' now there appear but 6 to the bare Eye. Milky Way.The Milky Way is crowded with infinite Numbers of small Stars, from whence, as is usually thought, its Whiteness appears; which is a Discovery entirely owing to the Telescope; but whether the Whiteness proceeds from the Smallness of those numberless Stars, their Nearness to one another, or their immense Distances, we can't. yet certainly determine, but must leave to Time and future Observations.
How endless is the Extent of the Divine Power and Goodness, said she, and how far are we yet from knowing the Bounds of the Starry World! But, Sir, your hinting, that formerly there were seven where now there appear but six Stars in the Pleiades, reminds me of your Promise, to acquaint me with the History of some Appearances of New Stars, and Disappearance of others, in Cassiopæia's Chair, and in some other Places in the Heavens.
I Think, said the Lady, I have enough for this Time, about the Sun and the fixed Stars; I will consider of it, and have Recourse to the Books you recommend to me, and trouble you the next Time, about the Planets, in the Order as they are in, with Respect to the Sun; only give me leave to break in upon it, with regard to our own Planet, the Earth, and her Attendant, the Moon. With which, out of Self-love, or rather Inclination to the Place of our Birth and Abode, I would fain begin, if you don't judge it to be improper.
By no Means, Madam, said I; for many things will occur in our Discourses ​about the Moon and Earth, which are very common and obvious Appearances, and which thoroughly accounted for and explained, will render the Knowledge of the other Planets much more easy and intelligible.