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A NEW CALENDAR
FOR CHINA
THE SOLAR YEAR
IN CONTEXT
KEY ASTRONOMER
Guo Shoujing (1231–1314)BEFORE
100 bce Emperor Wu of
the Han Dynasty establishes
the Chinese calendar based
on a solar year.46 bce Julius Caesar reforms
the Roman calendar using a
year-length of 365 days and
6 hours, and adds a leap day
every four years.AFTER
1437 The Timurid astronomer
Ulugh Beg measures the
solar year as 365 days,
5 hours, 49 minutes, and
15 seconds using a 164-ft
(50-m) gnomon (the central
column of a sundial).1582 Pope Gregory adopts
the Gregorian calendar as a
reform of the ancient Julian
calendar by using a 365.25-day
year, the same year as Guo’s
Shoushi calendar.T
he traditional Chinese
calendar is a complex blend
of lunar and solar cycles,
with 12 or 13 lunar months matched
up to the solar-derived seasons.
It had first been formalized in the
1st century bce during the Han
Dynasty, and used a solar year of
365.25 days (365 days and 6 hours).China’s calculations were ahead
of the West’s: 50 years later, this
same period was used by Julius
Caesar to create the Roman
Empire’s Julian system.
By the time the Mongol leader
Kublai Khan conquered most of
China in 1276, a variant of the
original calendar, the Daming
calendar, was in use, but was
centuries old and in need of
correction. The khan decided to
impose his authority with a new,
more accurate calendar, which
became known as the Shoushi
(“well-ordered”) calendar. The task
of creating it was entrusted to
Guo Shoujing, the khan’s brilliant
Chinese chief astronomer.Measuring the year
Guo’s job was to measure the
length of the solar year, and to
this end he set up an observatory
in Khanbaliq (the “City of the
Khan”), a new imperial capital
that would one day become known
as Beijing. The observatory may
have been the largest anywhere
in the world at the time.
Working with mathematician
Wang Chun, Guo began a series
of observations tracking the motion
of the sun throughout the year.A trained engineer, Guo Shoujing
invented a water-powered version
of an armillary sphere, which is an
instrument used to model the
positions of celestial bodies.