What is' timing '

      To determine and maintain a certain time scale through certain technical means, and to transmit the time information of this scale through certain means for use by users, this whole set of work is called "time service" in China and time service in other countries.

      The term 'bestowing time' may come from the text in the 'Yao Dian' of the Book of Shangshu, which reads' Naiming Xihe, Qin Ruo Haotian, calendar like the sun, moon, and stars, respectfully bestowing time '. With the development of human society and the progress of science and technology, the scale and quality of time service are constantly improving, and time service technology has made significant progress. Time service has become an indispensable public welfare project in the national economy and people's livelihood, and even relates to national security.

      1、 What is timing?

      The term "timing" has been used for many years, such as Zhang Heng, who invented the seismograph in the Eastern Han Dynasty, who said "to regulate the heavens and the earth, timing follows the countryside", and Su Shi of the Song Dynasty, who said "timing and administration are also the norm for prefectures". Of course, not only these well-known celebrities have said it, but the term "timing" has also appeared multiple times in many other classics.

      In ancient times, there was a group of astrologers around the emperor who were responsible for formulating the calendar and telling the people the established calendar. This was called "honoring the time of the day to teach the people", so that farmers would not miss the time for sowing, fertilizing, and harvesting.

      In today's society, communication systems, power systems, financial systems, navigation systems, etc., which are closely related to our daily work, life, and social governance, all rely on high-precision time synchronization for their effective operation. It is the 100 meter race in sports, where the difference between the champion and runner up may be just a few tenths of a second. Therefore, an accurate and stable time benchmark and high-precision timing system play an extremely important role in the normal operation of modern society. Scientists from various countries are making unremitting efforts to improve timing accuracy.

      Let's take a look at the methods of timing using two pictures below.

      From the above two figures, it is not difficult to see that there are many ways of timing. The accuracy of satellite timing can reach the nanosecond level, and the unit of time can be too small for us to imagine.

2、 How do satellites provide time?

      The preferred satellite timing system in China is the Beidou satellite system, which uses an atomic clock and has a difference of less than 30 nanoseconds from the world coordinate time, which can maintain time accuracy very well. GPS is controlled by the US military, and in exceptional times, the US military can turn off GPS in a certain area or even send incorrect timing information, causing users in that area to have incorrect time and causing significant interference. When the Beidou system in China was not yet in use, there were incidents where the entire city was unable to communicate due to abnormal GPS signals.

      The Beidou satellite system has another advantage in timing that other satellite navigation systems do not have, which is the use of geostationary orbit satellites. The timing error of this type of satellite does not change much throughout the entire Chinese region, and the error changes relatively slowly over time. The timing stability is high in both time and space.