Light-year is not a unit of time, but a unit of length. The light year is used to measure the distance that light travels along a straight line in the vacuum of the universe for one year. It is used to measure the space-time distance between celestial bodies. Its literal meaning is the distance that light travels along a straight line in the vacuum of the universe for one year. , is 9,460,730,472,580,800 meters, which is the unit in which time and the speed of light are calculated.

"Year" is a unit of time, but although "light year" has the word "year", it is not a unit of time, but an astronomical unit for measuring the space-time distance of celestial bodies. The distances between celestial bodies in the universe are very far away.

If we use the meters and kilometers (kilometers) we use daily as measurement units, the numbers used to measure the distance between celestial bodies will often number in the dozens or dozens of digits. Very inconvenient. So astronomers created a new unit of measurement - the light year, which is the distance traveled by light in a vacuum in one year.

Extended information:

Measuring method of light year:

Observe the same object at two points, two lines of sight and two The connection between the points can form an isosceles triangle. According to the size of the vertex angle of the triangle, the height of the triangle can be known, which is the distance of the object from the observer. Using the distance between the sun and the earth as the baseline and measuring the position changes of some stars, the distances of these stars can be obtained.

When we want to measure the distance between stars, we can choose the position of the Earth in the orbit in January as the starting point, the position of the Earth in the orbit in July as the end point, and the line segment connecting these two points as "Bottom",

Then observe the position of the measured star relative to nearby background objects in January and July respectively, and you can get the star's parallax value, so you can use the "bottom" The length and parallax values ??calculate the star's distance.

Baidu Encyclopedia-Lightyear