26. VENUS, the next Planet in order, is computed to be 59 millions of
miles from the Sun; and by moving at the rate of 69 thousand miles every
hour in her Orbit (as in the circle marked ♀), she goes round the Sun in
224 days 17 hours of our time nearly; in which, though it be the full
length of her year, she has only 9-1/4 days, according to BIANCHINI’s
observations; so that in her, every day and night together is as long as
24-1/3 days and nights with us. This odd quarter of a day in every year
makes every fourth year a leap-year to Venus; as the like does to our
Earth. Her diameter is 7906 miles; and by her diurnal motion the
inhabitants about her Equator are carried 43 miles every hour: besides
the 69,000 above-mentioned.
[Sidenote: Her Orbit lies between the Earth and Mercury.]
27. Her Orbit includes that of Mercury within it; for at her greatest
Elongation, or apparent distance from the Sun, she is 96 times his
breadth from his centre; which is almost double of Mercury’s. Her Orbit
is included by the Earth’s; for if it were not, she might be seen as
often in Opposition to the Sun as in Conjunction with him; but she was
never seen 90 degrees, or a fourth part of a Circle, from the Sun.
[Sidenote: She is our morning and evening Star by turns.]
28. When Venus appears west of the Sun she rises before him in the
morning, and is called the _Morning Star_: when she appears east of the
Sun she shines in the evening after he sets, and is then called the
_Evening Star_: being each in it’s turn for 290 days. It may perhaps be
surprising at first, that Venus should keep longer on the east or west
of the Sun than the whole time of her Period round him. But the
difficulty vanishes when we consider that the Earth is all the while
going round the Sun the same way, though not so quick as Venus: and
therefore her relative motion to the Earth must in every Period be as
much slower than her absolute motion in her Orbit, as the Earth during
that time advances forward in the Ecliptic; which is 220 degrees. To us
she appears through a telescope in all the various shapes of the Moon.
29. The Axis of Venus is inclined 75 degrees to the Axis of her Orbit;
which is 51-1/2 degrees more than our Earth’s Axis is inclined to the
Axis of the Ecliptic: and therefore the variation of her seasons is much
greater than of ours. The North Pole of her Axis inclines toward the
20th degree of Aquarius, our Earth’s to the beginning of Cancer; and
therefore the northern parts of Venus have summer in the Signs where
those of our Earth have winter, and _vice versâ_.
[Sidenote: Remarkable appearances.]
30. The [6]artificial day at each Pole of Venus is as long as 112-1/2
[7]natural days on our Earth.
[Sidenote: Her Tropics and polar Circles, how situated.]
31. The Sun’s greatest Declination on each side of her Equator amounts
to 75 degrees; therefore her[8] Tropics are only 15 degrees from her
Poles; and her [9]Polar Circles as far from her Equator. Consequently,
the Tropics of Venus are between her Polar Circles and her Poles;
contrary to what those of our Earth are.
[Sidenote: The Sun’s daily Course.]
32. As her annual Revolution contains only 9-1/4 of her days, the Sun
will always appear to go through a Sign, or twelfth Part of her Orbit,
in little more that three quarters of her natural day, or nearly in
18-3/4 of our days and nights.
[Sidenote: And great declination.]
33. Because her day is so great a part of her year, the Sun changes his
Declination in one day so much, that if he passes vertically, or
directly over head of any given place on the Tropic, the next day he
will be 26 degrees from it: and whatever place he passes vertically over
when in the Equator, one day’s revolution will remove him 36-1/4 degrees
from it. So that the Sun changes his Declination every day in Venus
about 14 degrees more at a mean rate, than he does in a quarter of a
year on our Earth. This appears to be providentially ordered, for
preventing the too great effects of the Sun’s heat (which is twice as
great on Venus as on the Earth) so that he cannot shine perpendicularly
on the same places for two days together; and by that means, the heated
places have time to cool.
[Sidenote: To determine the points of the Compass at her Poles.]
34. If the inhabitants about the North Pole of Venus fix their South, or
Meridian Line, through that part of the Heavens where the Sun comes to
his greatest Height, or North Declination, and call those the East and
West points of their Horizon, which are 90 degrees on each side from
that point where the Horizon is cut by the Meridian Line, these
inhabitants will have the following remarkables.
[Sidenote: Surprising appearances at her Poles;]
The Sun will rise 22-1/2 degrees[10] north of the East, and going on
112-1/2 degrees, as measured on the plane of the [11]Horizon, he will
cross the Meridian at an altitude of 12-1/2 degrees; then making an
entire revolution without setting, he will cross it again at an altitude
of 48-1/2 degrees; at the next revolution he will cross the Meridian as
he comes to his greatest height and declination, at the altitude of 75
degrees; being then only 15 degrees from the Zenith, or that point of
the Heavens which is directly over head: and thence he will descend in
the like spiral manner; crossing the Meridian first at the altitude of
48-1/2 degrees; next at the altitude of 12-1/2 degrees; and going on
thence 112-1/2 degrees, he will set 22-1/2 degrees north of the West; so
that, after having been 4-5/8 revolutions above the Horizon, he descends
below it to exhibit the like appearances at the South Pole.
35. At each Pole, the Sun continues half a year without setting in
summer, and as long without rising in winter; consequently the polar
inhabitants of Venus have only one day and one night in the year; as it
is at the Poles of our Earth. But the difference between the heat of
summer and cold of winter, or of mid-day and mid-night, on Venus, is
much greater than on the Earth: because in Venus, as the Sun is for half
a year together above the Horizon of each Pole in it’s turn, so he is
for a considerable part of that time near the Zenith; and during the
other half of the year, always below the Horizon, and for a great part
of that time at least 70 degrees from it. Whereas, at the Poles of our
Earth, although the Sun is for half a year together above the Horizon,
yet he never ascends above, nor descends below it, more than 23-1/2
degrees. When the Sun is in the Equinoctial, or in that Circle which
divides the northern half of the Heavens from the southern, he is seen
with one half of his Disc above the Horizon of the North Pole, and the
other half above the Horizon of the South Pole; so that his center is in
the Horizon of both Poles: and then descending below the Horizon of one,
he ascends gradually above that of the other. Hence, in a year, each
Pole has one spring, one harvest, a summer as long as them both, and a
winter equal in length to the other three seasons.
[Sidenote: At her polar Circles;]
36. At the Polar Circles of Venus, the seasons are much the same as at
the Equator, because there are only 15 degrees betwixt them, § 31; only
the winters are not quite so long, nor the summers so short: but the
four seasons come twice round every year.
[Sidenote: At her Tropics;]
37. At Venus’s Tropics, the Sun continues for about fifteen of our weeks
together without setting in summer; and as long without rising in
winter. Whilst he is more than 15 degrees from the Equator, he neither
rises to the inhabitants of the one Tropic, nor sets to those of the
other: whereas, at our terrestrial Tropics he rises and sets every day
of the year.
38. At Venus’s Tropics, the Seasons are much the same as at her Poles;
only the summers are a little longer, and the winters a little shorter.
[Sidenote: At her Equator.]
39. At her Equator, the days and nights are always of the same length;
and yet the diurnal and nocturnal Arches are very different, especially
when the Sun’s declination is about the greatest: for then, his meridian
altitude may sometimes be twice as great as his midnight depression, and
at other times the reverse. When the Sun is at his greatest Declination,
either North or South, his rays are as oblique at Venus’s Equator, as
they are at _London_ on the shortest day of winter. Therefore, at her
Equator there are two winters, two summers, two springs, and two autumns
every year. But because the Sun stays for some time near the Tropics,
and passes so quickly over the Equator, every winter there will be
almost twice as long as summer: the four seasons returning twice in that
time, which consists only of 9-1/4 days.
40. Those parts of Venus which lie between the Poles and Tropics, and
between the Tropics and Polar Circles, and also between the Polar
Circles and Equator, partake more or less of the Phenomena of these
Circles, as they are more or less distant from them.
[Sidenote: Great difference of the Sun’s amplitude at rising and
setting.]
41. From the quick change of the Sun’s declination it happens, that when
he rises due east on any day, he will not set due west on that day, as
with us; for if the place where he rises due east be on the Equator, he
will set on that day almost west-north-west; or about 18-1/2 degrees
north of the west. But if the place be in 45 degrees north latitude,
then on the day that the Sun rises due east he will set north-west by
west, or 33 degrees north of the west. And in 62 degrees north latitude
when he rises in the east, he sets not in that revolution, but just
touches the Horizon 10 degrees to the west of the north point; and
ascends again, continuing for 3-1/4 revolutions above the Horizon
without setting. Therefore, no place has the forenoon and afternoon of
the same day equally long, unless it be on the Equator or at the Poles.
[Sidenote: The longitude of places easily found in Venus.]
42. The Sun’s altitude at noon, or any other time of the day, and his
amplitude at rising and setting, being so different at places on the
same parallels of latitude, according to the different longitudes of
those places, the longitude will be almost as easily found on Venus as
the latitude is found on the Earth: which is an advantage we can never
enjoy, because the daily change of the Sun’s declination is by much too
small for that purpose.
[Sidenote: Her Equinoxes shift a quarter of a day forward every year.]
43. On this Planet, wherever the Sun crosses the Equator in any year, he
will have 9 degrees of declination from that place on the same day and
hour next year; and will cross the Equator 90 degrees farther to the
west; which makes the time of the Equinox a quarter of a day (almost
equal to six of our days) later every year. Hence, although the spiral
in which the Sun’s motion is performed, be of the same sort every year,
yet it will not be the very same, because the Sun will not pass
vertically over the same places till four annual revolutions are
finished.
[Sidenote: Every fourth year a leap-year to Venus.