Astronomy Explained Upon Sir Isaac Newton's Principles: And made easy to those who have not studied mathematicsFerguson, James
Science
Astronomy Explained Upon Sir Isaac Newton's Principles: And made easy to those who have not studied mathematics
Ferguson, James
Astronomy -- Early works to 1800
The different Angles made by the Ecliptic and Horizon.]
But, because all who read this Treatise may not be provided with Globes,
though in this case it is requisite to know how to use them, we shall
substitute the Figure of a Globe; in which _FUP_ is the Axis, ♋_TR_ the
Tropic of Cancer, _LT_♑ the Tropic of Capricorn, ♋_EU_♑ the Ecliptic
touching both the Tropics which are 47 degrees from each other, and _AB_
the Horizon. The Equator, being in the middle between the Tropics, is
cut by the Ecliptic in two opposite points, which are the beginnings of
♈ Aries and ♎ Libra. _K_ is the Hour circle with its Index, _F_ the
North pole of the Globe elevated to the Latitude of _London_[60], namely
51-1/2 degrees above the Horizon; and _P_ the South Pole depressed as
much below it. Because of the oblique position of the Sphere in this
Latitude, the Ecliptic has the high elevation _N_♋ above the Horizon,
making the Angle _NU_♋ of 62 degrees with it when ♋ Cancer is on the
Meridian, at which time ♎ Libra rises in the East. But let the Globe be
turned half round its Axis, till ♑ Capricorn comes to the Meridian and ♈
Aries rises in the East, and then the Ecliptic will have the low
elevation _NL_ above the Horizon making only an Angle _NUL_ of 15
degrees, with it; which is 47 degrees less than the former Angle, equal
to the distance between the Tropics.
[Sidenote: Least and greatest, when.]
276. The smallest Angle made by the Ecliptic and Horizon is when Aries
rises, at which time Libra sets: the greatest when Libra rises, at which
time Aries sets. From the rising of Aries to the rising of Libra (which
is twelve [61]Sidereal hours) the angle increases; and from the rising
of Libra to the rising of Aries it decreases in the same proportion. By
this article and the preceding, it appears that the Ecliptic rises
fastest about Aries and slowest about Libra.
Public-domain text, read in full here on John Shaqi.
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