Nanjing’s ancient Observatory
In Nanjing, next to Lake Xuanwu (玄
武) in the middle of the city you can find the Purple Mountain (紫金山).
The Purple Mountain is now surrounded by the city of Nanjing, but is
not urbanised itself. This makes it an oasis between the old city on
one side and the vast new districts on the other side of the
mountain. On and around the mountain you will find the mausoleums of
the first Ming (洪武) emperor, who makes Nanjing the capital, and Sun
Yat-sen (孙中山) the first president of China. You can take a cable
car to the top of the mountain and from there walk back to the city at
the bottom of the mountain. You walk there between the trees and the
view is beautiful.
The Nanjing Observatory is
located on one of the peaks of 紫金山. The observatory is only used as
part of the university. The telescopes are no longer used because the
light from the city and air pollution make observations impossible. It
was never an ideal place for an observatory. The climate is hot and
humid in Nanjing and it is often cloudy.
Still, the observatory was
used for observations and accurate timing until the twentieth
century. There is another meridian viewer from after the revolution. A
meridian is positioned exactly on the local meridian and is used to
measure when a star, or the Sun, passes the local meridian. With this
the local time can be calculated. The photo shows one of the meridian
viewers. It is a small viewer because it was not intended to look deep
into the universe, it is a measuring instrument to measure the time of
the passage of a star. The viewer is therefore small, but very
accurate.
The observatory was also
close to power during the time when Nanjing was the capital. The
observatory still contains a number of historical instruments from
long ago. Astronomical observations were of great importance to the
Chinese emperors. The emperor ruled with the mandate of
heaven. Heaven, the position of the planets, set the correct date for
affairs of state. So the calendar had to be correct. The latter was
not so easy because in China they had a calendar that was based on
both the movement of the Sun and the Moon. And the calendar was
wrong. So the new Ming dynasty needed an observatory. A number of
instruments were brought over from Kaifing and set up on Purple
Mountain in Nanjing, close to the New Palace. The photos show two of
the large instruments the Chinese used to measure the positions of the
planets. Such a measuring instrument is called an armillary. The
oldest were made in 1437, before the start of the Ming Dynasty. And
these are copies of even older instruments.
When
Matteo Ricci visited the observatory on his
way to Beijing, he noticed that the instruments at the observatory
were not at all suitable for that location. After all, they were made
for Kaifeng, which is at a higher latitude. Because Matteo Ricci had
also studied astronomy during his missionary training, he must have
been familiar with an armillary and how to operate such an
instrument. Armillaria were used in Europe to measure the positions of
the planets, Sun and stars. He knew that the axis of an ecliptic
armillary should point towards the pole star, so he quickly saw that
there was something wrong with the armillary in Nanjing. This prompted
him to write to Rome that a missionary astronomer in China might
accomplish a lot. A calendar was essential for affairs of state, but
an accurate calendar was a concern for Chinese astronomers.
Much later, one of Matteo
Ricci's successors stood next to such a beautiful bronze instrument
again, this time in Beijing. Ferdinand Verbiest had come to China long
after Ricci. The Jesuits had already made a much improved calendar for
the emperor, but intrigues at court had disgraced the
Jesuits. Verbiest had one chance to show that the improved calendar
was better than the Chinese calendar. He had to make a number of
predictions, including the height of the sun on a given date. Height
was measured with a gnomon. A gnomon is a type of sundial that is only
used to measure the angle between the Sun and the horizon. Because a
gnomon is positioned exactly on the local meridian (in a north-south
direction), it shows the angle when it is greatest. That gnomon that
Ferdinand Verbiest once stood next to to prove his calendar is right,
later moved from Beijing to Nanjing. And now it is on the Purple
Mountain, next to the other old bronze instruments and close to the
modern version of the gnomon: the meridian viewer.