Home » Sunday » Now and Then
Tower used to make age’s best calendar
Print Edition
登封观星台 (dengfeng guanxingtai) Dengfeng Observatory
Standing in “The Center of Heaven and Earth,” a group of historical monuments 7.5 kilometers to the southeast of Dengfeng in central China’s Henan Province, Dengfeng Observatory is the oldest facility for stargazers still standing in the country.
The observatory, also known as the Gaocheng Astronomical Observatory, was built by Guo Shoujing (1231–1316), a famous Chinese astronomer, engineer and mathematician, at the behest of Kublai Khan, the first emperor of the Yuan Dynasty (1271-1368).
After consolidating his power as a new emperor in China, the grandson of the Mongol Empire founder Genghis Khan, ordered a group of famous astronomers, including Guo, to make a more accurate calendar to replace older ones.
Like other Chinese emperors, Kublai Khan paid great attention to calendars, some of which were produced as early as the Warring States Period (476-221 BC). They wanted to know about astronomical occurrences to make important decisions and conduct imperial events according to “heavenly” phenomena.
To obtain accurate and thorough observations for calculations, Guo and his team asked the Kublai Khan for approval to build 27 observatories, with the northernmost one at Tiele near the Yenisei River in today’s Siberia and the southernmost one established on the Xisha Islands in the South China Sea, spanning several thousand kilometers.
Among the 27 observatories, the Dengfeng Observatory was the first one built, in 1276. It was located at the middle of a meridian that linked up all the astronomical facilities from the north to the south. As a result, it was deemed a crucial spot to observe the movement of the celestial bodies and record time.
Built of rubbed bricks and in the shape of a flat-top pyramid, the Dengfeng Observatory is more than 16 meters wide at the bottom and about 8 meters at the top. The tower itself stands 9.46 meters tall, but its height reaches 12.62 meters when the two structures on top are included.
To the northern side of the tower, it is hugged by two symmetrical spiral stairways serving as both entries and exits.
From the bottom to a horizontal stone bar placed on top of the two structures, there is a vertical gutter which was designed as the “altimeter.” Aligned with the gutter and extending 31.19 meters to the north, a shigui or “sky ruler” was built on the ground to measure the length of the shadow. Made of 36 bluestones, the “sky ruler” is 0.53 meters wide and has two water grooves to check its levelness.
Thanks to its meticulous and scientific design, the precision of its measurements was within 2 millimeters. For instance, at winter solstice, the shadow was exactly as long as the “sky ruler.”
The Winter Solstice is one of the four key season-defining days on the traditional Chinese calendars, and the other three are vernal equinox, autumnal equinox and summer solstice.
In 1281, based on their observation and calculations at their observatories, including the Dengfeng Observatory, Guo and his colleagues introduced the Shoushi Calendar, or the Season-Granting Calendar, which was later deemed the most accurate calendar at the time in the world.
The new calendar determined that the length of the tropical year was 365.2425 days, a figure that is only 26 seconds off the current measurement of the year and the same as the value of the Gregorian Calendar, but it was produced more than 300 years earlier.
In July 2010, the Dengfeng Observatory was among structures added to the World Heritage List of UNESCO.
圭表 (guibiao) Gnomon
Guibiao is a stationary arm that projects a shadow on a sundial to indicate time or season. According to historical records, people in China began to use guibiao to indicate time as early in the 7th century BC.
They called the stationary arm, usually an erected pole or stone pillar, gui and the horizontal ruler on the ground biao.
Ancient Chinese used the lengths of the shadow obtained by guibiao at midday to define seasons and the tropical year or the solar year.
They also used guibiao to help define the 24 fortnightly solar terms in Chinese calendars, such as Start of Spring, Awakening of Insects, Vernal Equinox, Grain Rain, Limit of Heat, Frost Descent and Winter Solstice, and they were designed to describe specific astronomical and natural phenomena and provide guidance for farmers in their productive activities.
However, the key function of guibiao was to identify the date of the Winter Solstice and confirm the number of days of a tropical year.
In fact, the Dengfeng Observatory, which is the oldest existing astronomical facility in China, is an enlarged guibiao.
- About Us
- |
- Terms of Use
- |
-
RSS - |
- Privacy Policy
- |
- Contact Us
- |
- Shanghai Call Center: 962288
- |
- Tip-off hotline: 52920043
- 沪ICP证：沪ICP备05050403号-1
- |
- 互联网新闻信息服务许可证：31120180004
- |
- 网络视听许可证：0909346
- |
- 广播电视节目制作许可证：沪字第354号
- |
- 增值电信业务经营许可证：沪B2-20120012
Copyright © 1999- Shanghai Daily. All rights reserved.Preferably viewed with Internet Explorer 8 or newer browsers.
