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
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.]
Public-domain text, read in full here on John Shaqi.
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