Draw a time axis, which is the number axis in mathematics. Then, the second second is the interval between one and two, and the end point of the second second is the point of two, which is an instant. The second second and the second mean the same thing, and the end of the second third is the point of six.
In fact, in physics, a second is the same as an hour, and it is also a period of time, but the length is different.
1 international second is equivalent to:
1/60 points
1/3600 hours
1/86400 days (time unit of the International Astronomical Union)
1/3 1,557,600? Julian year (time unit of the International Astronomical Union)
Extended data:
1s = 10 3 ms (milliseconds) = 10 6 μ s (microseconds) = 10 9 ns (nanoseconds) =10/2ps (picoseconds) = 65438.
Therefore,1PC = 360× 60× 60 ÷ 2π×1au = 206265au = (3.08568×10/6) m = 3.26/kloc-0.
Astronomers usually use parsec instead of astronomical units to describe the distance of celestial bodies. This is not only because the parsec number is easier to calculate, but also because of historical reasons.
The greater the parallax of celestial bodies, the closer the distance is. On the contrary, the smaller the parallax, the farther away from us. The nearest star (except the sun) is about 1.29pc(4.22 light years), which lies in the parsec of proxima centauri.
Parsec is the reciprocal of annual parallax. When the annual parallax of the celestial body is 0. 1 ",the distance is 10 parsec, and when the annual parallax of the celestial body is 0.0 1", the distance is 100 parsec, and so on.
Before the Han dynasty, "time" refers to the season, and "time" is equivalent to the current season. There are four seasons in a year, so a year is also called "four seasons".
After the Han dynasty, "time" no longer represents the season, but is used to represent the unit of calculating time. At that time, people divided a day into 12 hours on average, and "one hour" was equal to two hours now. People are used to calling this "hour".
In some classical books, we often see the word "time". Many people mistakenly think that an hour is an hour now, which is actually incorrect. The ancient word "night watch" and "night watch" refers to time, and there are two hours between the first watch and the second watch and the third watch.
References:
Baidu encyclopedia-second