How did ancient ships find their way?

How to find ancient ships

Direction of travel?

With the development of technology, navigation has become an indispensable tool for people to go out. No need to ask for directions, just with navigation in hand, you can travel around the world. Navigation has provided great convenience for people's lives, but in ancient times when there was no navigation, how did people identify the position and direction?

Ancient Navigation

As early as the Warring States Period more than 2,000 years ago, the wise ancient people had discovered that magnets have the ability to point to polarity. So they used the polarity of magnets to invent the Si Nan. Guiguzi wrote: "When the people of Zheng go to get jade, they must carry the Si Nan cart with them, so that they will not get lost." From the records in the classics, we can also see that the Si Nan played an indispensable role in the travel of ancient people.

Sinan

Si Nan was continuously improved by humans, and one of the four great inventions of ancient China, the compass, appeared. The appearance of the compass was not achieved overnight, but after a very long period of improvement. The improved works of Si Nan, the compass fish and the floating magnetic needle, were mainly recorded in the Tang and Song dynasties. For example, the "Shen Ji Secret Book" said: "The needle method was not passed down in ancient times, and it was first made by Xuan Zhen in ancient times." Xuan Zhen was a Tang Dynasty person who was good at physics. The preparation method of the compass fish was recorded in "Wu Jing Zong Yao". The book said: "Use thin iron leaves to cut, two inches long and five points wide, with sharp heads and tails like fish shapes, put them in charcoal fire and burn them. When they are red, use an iron seal to seal the fish head out of the fire, and put the tail directly in the position of the child. Dip it in a basin of water and stop when the tail is submerged for several minutes, and collect it in a sealed container." This book was written in the Northern Song Dynasty.

Compass fish

The floating magnetic needle was also recorded in the Northern Song Dynasty. It was specifically recorded in the masterpiece of the famous scientist Shen Kuo, Mengxi Bitan. In Volume 24, it says: "The experts rubbed the needle tip with a magnet and it could point south."

Floating magnetic needle

Compared with on land, humans are more likely to get lost when sailing, and the compass at this time cannot fully meet the navigation needs. In this situation, humans invented more tools that can indicate direction during sailing, and these tools helped humans embark on the great road of navigation.

Getting lost during a voyage is extremely dangerous. Faxian, a monk from the Eastern Jin Dynasty, once wrote: "The sea is boundless and I cannot tell east from west. I can only look to the sun, the moon and the stars to move forward." This shows that in addition to using geomagnetic navigation, the ancients also used the laws of astronomy for navigation. Among them, the most famous astronomical navigation tool is the star-guiding board that accompanied Zheng He on his seven voyages to the West.

The star-pulling board is a tool used in ancient my country to carry out navigation and navigation using astronomical positioning technology - star-pulling. Its main principle is to convert the vertical height measured by the star-pulling board and the length of the fiber rope to calculate the altitude angle of the North Star, and then determine the geographical latitude of the location.

Star Puller Board

Twenty pages of Zheng He's nautical charts are preserved in "Wubeizhi", four of which are "Star-Guiding Charts for Crossing the Ocean". The observation instruments used by the crew in the charts are star-guiding boards.

Crossing the Ocean to Pull the Stars

According to records, the star-pulling board is composed of 12 pieces of ebony boards with scales and sides ranging from 2 to 24 cm. The observer needs to hold the star-pulling board so that the board surface is perpendicular to the sea level, the lower edge is perpendicular to the sea-sky boundary, and the upper edge is connected to the celestial body to be measured. A long rope is drawn on the board to fix the distance between the star-pulling board and the observer's eyes. The calculation units are "finger" and "angle". One finger is about 1.9° today, which is equivalent to four angles.

In the Marine Astronomy Exhibition Hall of the National Maritime Museum, there is an interactive screen for experiencing the principle of the star-pulling board.

Interactive experience screen in the Marine Astronomy Exhibition Hall of the Marine Museum

In the West, there is also a sextant used to measure stars for navigation. The principle of the sextant is very simple, that is, the reflection angle of light is equal to the incident angle. When using it, the observer needs to hold the sextant and rotate the index mirror so that the celestial body that appears in the field of view coincides with the sea level. The altitude angle of the celestial body can be read according to the rotation angle of the index mirror, and the error is about ±0.2°~±1°.

Interactive experience screen in the Marine Astronomy Exhibition Hall of the Marine Museum

The principle of the sextant was proposed by Newton. In 1732, the British Navy began to install the original instrument on ships. Because the maximum measuring angle at that time was 90 degrees, it was called an octant. In 1757, Captain John Campbell increased the measuring angle of the octant to 120 degrees, and developed it into a sextant. Although the measuring angle of the sextant was gradually increased to 144 degrees, its name remained unchanged.

The crystal decoration above the entrance to the Marine Astronomy Exhibition Hall of the National Museum of Marine Life is in the shape of a sextant.

Marine Astronomy Hall

Entrance sextant decoration

In addition, the Jingtianweidi exhibition area also displays sextants and octants produced by various countries in the world at different times.

Jingtianweidi Exhibition Area

Early English Octant

German Sextant

Japanese Sextant

Swiss Sextant

British Pocket Sextant

Prologue of the Astronomical Office (Various Navigation Methods)

From the Polynesians who used special hand gestures combined with the stars in the sky to determine direction, to today's humans launching satellites into space for marine navigation, humans have never stopped exploring the sea and the starry sky, constantly improving equipment and breaking through limits, from the compass to the Beidou satellite navigation system, from simple devices to major national equipment, all demonstrate the progress of human civilization and technology.

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Source: National Maritime Museum