Astronomia Britannica exhibiting the doctrine of the sphere, and theory of the planets decimally by trigonometry, and by tables : fitted for the meridian of London ... / by John Newton ...

The Preface.

ALL Propositions Astronomical and Astro∣logical, have some dependence on the Sphere or Globe, for the better understand∣ing therefore of that which follows, it is fit that the Reader be somewhat acquaint∣ed with the doctrine thereof; that he know at least what a Globe is, and what the lines, circles and arches usually drawn thereon do represent. Now a Globe or Sphere, is an Analogical representation either of the Heavens or the Earth.

And in this Sphere or Globe there are ten imaginary circles whereof there are six great and foure small. A great circle is such a one as divideth the body of the Globe into two equal Hemispheres. And a small circle is that which divideth the same, into two unequal Hemispheres, wherof the one is more, the other less then half the body of the Globe or Sphere.

The six great circles are these. 1 The Horizon. 2 The Me∣ridian. 3 The Equinoctial. 4 The Zodiack. The fifft and sixt are the two colures.

The four lesser circles are, 1 The Tropick of Cancer. 2 The Tropique of Capricorn. 3 The circle Artick. 4 The circle Antarctick. And are all exprest in this annexed Diagram.

• 1 The Horizon w^ch is also called the Finitor, is a circle which

• divideth the visible part of the Heavens from the not visible, that is the lower Hemisphere from the higher, in the figure noted with A B.
• 2 The Meridian is a circle which passeth by the Poles of the World, and through the Zenith and Nadir, and is mark∣ed with A Z B N.
• 3 The Equinoctial is a Circle which divideth the whole Sphere into two equal parts, and is therefore equally distant from both the Poles, to which when the Sun cometh (which is twice in the Year) the Dayes and Nights are of equal length all the World over, this circle is noted with E F.
• 4 The Zodiack is a great circle which conteineth the 12 Signes, cutting in the very middle the Equinoctial in two points, which are the beginning of Aries and Libra, whereof the one half. viz. six Signes decline from the Aequator to the North Pole, and are therefore called the Northern Signes, as Aries ♈, Taurus ♉, Gemini ♊, Cancer ♋, Leo ♌; Virgo ♍. The o∣ther six decline towards the South Pole and are therfore cal∣ed the Southern Signes, as Libra ♎, Scorpio ♏, Sagittarius ♐, Ca∣pricornus ♑, Aquarius ♒, Pisces ♓.
• 5 The one of the Colures which dividing the Sphere into two parts passeth by the Poles of the World and the two E∣quinoctial points, called the Equinoctial Colure, and marked with C D.
• 6 The other Colure which dividing the Sphere also into two equal parts, passeth by the beginning of Cancer and Capri∣corn, and the Poles of the World, called the Solstitial Colure, and is the same with the Meridian as the Sphere is here pro∣jected.
• 7 The Tropick of Cancer is one of the lesser circles distant from the Equinoctial towards the North Pole 23 deg. 31 min. 30 seconds, or in Decimal Numbers, 23 deg. 525, to which when the Sun cometh he causeth the longest day, and shortest night to all Northern, the shortest day and longest

• night to all Southern inhabitants, and is noted with G ♋.
• 8 The Tropick of Capricorn is a circle distant from the E∣quinoctial towards the South Pole: 23 deg. 31 min. 30 seconds, or in Decimal numbers, 23 deg. 525 parts, to which when the Sun cometh, he maketh the longest day and shortest night, to all Southern the shortest day & longest night to all Northern Inhabitants, and is noted, with H ♑. These two circles are called of the Greeks 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉 à convertendo, because when the Sun toucheth any of these circles, he is at his greatest distance from the Aequator, and returneth thither again.
  [illustration]
• 9 The Artick circle is distant from the North pole of the world as much as the Tropick of Can∣cer is distant from the Equinoctial, and is noted with K L.
• 10 The Antar∣tick circle is di∣stant from the South Pole as much as the Tro∣pick of Capricorn is distant from the Aequator, and is noted with O M.

Besides these circles exprest upon the Globe, there are o∣ther circles not exprest, that are also in familiar use; but these being sufficient for our intended matter, omitting the rest, we will now speak of the several affections of the Sphere or Globe, and so proceed to practice.

According to the diverse habitude of the Aequator to the Ho∣rizon (which is either Paralel to it, or else cutteth it, and that

either in right or oblique angles) there is a threefold position or Situation of Spheres.

The first is of those that have either Pole for there Zenith or vertical point, with these the Aequator and Horizon are Parallel to each other, or rather indeed do make but one cir∣cle between them; and this is called a Parallel Sphere, and they which there inhabit (if any such be) see not the Sun or other Star either rising or setting, or higher or lower, in their diurnal revolution.

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Besides seeing that the Sun traverseth the whole Zodiack, in a Year, and that half the Zodiack is above the Horizon, and half under it, it comes to pass, that the Sun setteth not with them for the space of six moneths, nor giveth them any light, for the space of other six moneths, and so maketh but one artificial day and night of the whole Year. The second position of the Sphere is of those whose Zenith is in the Aequator, and this is called a right Sphere, in which

[illustration]

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all the Stars are observed to rise and set in an equal space of time, and to continue as long above the Horizon, as they do under it, as by the figure it doth appear, the day and night be∣ing alwayes of an equal length.

The third position of the Sphere agreeth to all other pla∣ces else, and is called an oblique Sphere, in which the dayes are sometimes longer then the nights, sometimes shorter, and sometimes of equal length: when the Sun is placed in the E∣quinoctial point, the dayes and nights are equal, but when he declineth from the Aequator, the dayes are observed to in∣crease, and when he declineth towards the opposite Pole the dayes decrease, as it is manifest in the first figure.

And thus having briefly shewed, what a Globe is, the lines thereon described, with the several affections belonging thereunto, what remayneth but that we now proceed to pra∣ctice, & shew there use as to the matter in hand; wch is to find

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the Declinations and Asceusions of the Sun and other Stars whether right or oblique, and divers other things depending on, or belonging to the Doctrine of the Spheare, the which we will shew first by Trigonometrical Calculation, and then by Tables.