light years
light years are not used to describe time, but to describe distance!
We can often see descriptions such as "how many light-years a certain star is from the earth" in news or science fiction movies. So what is the concept of a light-year and how far is it?
In our daily life, the most commonly used unit is "meter". This is because the height of human beings is between 1 meter and 2 meters, so the buildings and various facilities around us will be designed according to this ratio, but When we want to describe the distance between two cities or regions, it is not appropriate to use meters. Usually, "kilometers" are used to calculate and describe the distance.
Let’s enlarge the distance. In the solar system, when describing the distance between different celestial bodies, the data will become very large if kilometers are used. For example, the earth is about 380,000 kilometers away from the moon, and the closest distance to Mars At around 55 million kilometers, the data for planets farther away will only be larger, and it will be more convenient to create larger distance units at this time. When
calculates the distance between celestial bodies in the solar system, we generally use " astronomical unit " for calculation, usually English "AU" means astronomical unit, the distance of 1 astronomical unit is 149,597,870 kilometers, this value is also Average distance between earth and sun .
At the beginning, the astronomical unit is judged according to the distance between the earth and the sun. The distance between the sun and the earth is constantly changing. As the sun burns, the total mass of the sun will continue to decrease. After the gravity decreases, the earth will It will be farther and farther away from the sun, and time and space are relative, there will be a certain error in the astronomical unit observed on different planets, so at the 2012 International Astronomical Congress, the astronomical unit is strictly defined as "149597870700 meters", so far astronomy The unit will not change any more, even if the distance between the sun and the earth changes, the value of the astronomical unit is still fixed.
Using astronomical units to calculate the distance between celestial bodies in the solar system is also very convenient, that is, it gives us a lot of room for imagination. For example, Jupiter is about 5.2 astronomical units from the sun, and it is easy to imagine Jupiter The distance between the sun and the earth is about five times the distance between the earth and the sun. It is very convenient to imagine a three-dimensional map between the celestial bodies of the solar system in the brain. This is the advantage of suitable distance units.
"astronomical unit" is very convenient to describe the distance between celestial bodies in the solar system, but it is not enough when calculating the distance between different stars. The closest star to the sun is " Proxima ", Proxima Centauri About 265,000 AU from Earth, Proxima Centauri is only the closest star to humans. There are countless stars outside of Proxima Centauri. When judging the distance between these stars, AU is not enough.When
describes the distance between stars in the universe, or the size of galaxy , you need to use " light-year ", we know that the speed of light is the fastest speed in the universe, and light-year is the movement of light for one year The distance of one light-year is "9460730472580800 meters", which is about 63241 astronomical units, and the distance between the sun and Proxima Centauri is about 4.2 light-years, so the calculation is more convenient than astronomical units.
If the Oort cloud is calculated, then our solar system is a sphere with a diameter of about 2 light-years and a radius of about 1 light-year. The sun emits a beam of light, and it takes about a year to leave the Oort cloud.
The common view is that the diameter of the Milky Way is about 100,000 light-years. Some people think that the range of the Milky Way may be 200,000 light-years. It takes at least 100,000 years for light to travel from one end of the Milky Way to the other. The speed of the fastest aircraft is about 70.22 kilometers per second, and it takes about 4,000 years to leave the solar system at this speed...
If a person walks one step at a distance of 1 meter and takes one step per second, then he needs to be nonstop for nearly 300 million years. Only one light-year can be traveled. For today’s human beings, one light-year is an unimaginably long distance, but in the universe, one light-year is actually very short. At present, the scope of human astronomical exploration is about 10 billion light-years. , the range of the universe for us to observe is a full 90 billion light-years, and this range is called the "observable universe".
The universe is far larger than 90 billion light-years, but because the cosmic space itself is constantly expanding, and the age of the universe is 13.82 billion years, after the expansion of the universe exceeds the speed of light at a certain moment, the stars that are far away from us emit light. The light will never reach the earth due to the expansion of the universe. The observable space within this distance is the " observable universe ", and the range is about 90 billion light-years.
The current goal of human beings is to explore the planets in the solar system, and the next step is to leave the solar system to explore other star systems , light-years are enough for us to use, maybe when human technology is developed enough to explore the universe is wide enough, it will create more Large astronomical units to use.
