On a moonlit night, the sky is full of stars. When we look up at the stars, we see how they looked in the past. Of course, the starlight is real when it comes to our eyes. It’s just that these starlights need to travel across a long time and space to reach the earth. At this time The light they emit now will take several years or thousands of years to reach the earth and be seen by us.
The picture above is the beautiful Milky Way. The photographer took it near the Chilean Andes at an altitude of 5,000 meters. The bright Jupiter bulges in the center of the Milky Way. On its right side, it is obviously darker and yellower. The giant star Antares, while on the far right edge is the Small Magellanic Cloud, one of the satellite galaxies of the Milky Way. Source: NASA official website
In a narrow sense, "stars" refer to those luminous "dots" in the night sky, which can generally be divided into the following categories:
1. Within the solar system Some planets closer to the earth, such as Venus, Jupiter, Saturn, etc.;
2. Sometimes you can see those moving stars in the night sky. They may be artificial satellites or the International Space Station, such as our country's Dongfanghong No. 1 may be visible to the naked eye;
3. The stars that are most visible to the naked eye are stars, such as the Big Dipper, Sirius, Polaris, Altair, Vega, etc. These stars are all a few meters away from us. Within the range of ten to hundreds of light years;
4. The last category is extragalactic galaxies, but it is very difficult to see extragalactic galaxies with the naked eye because they are too far away from us. This includes those relatively close to the Milky Way. The Large and Small Magellanic Clouds, the Andromeda Galaxy, the Triangulum Galaxy, and the farthest one is the Triangulum Galaxy, which is about 3 million light-years away from us.
The latest data on the diameter of the Milky Way is 200,000 light-years. The solar system is located on one of its spiral arms, about 26,000 light-years from the center of the galaxy. Generally, the stars visible to our naked eyes are "small" in the picture above. Within the "white circle" range.
We all know that the speed of light is 300,000 kilometers per second, and human eyes see objects because light enters our eyes. Then the light emitted by an object reaches our eyes not instantaneously; It takes time. Especially when the distance is so large that the light travel time cannot be ignored. For example, the average distance between the sun and the earth is 150 million kilometers, and it takes about 8 minutes and 20 seconds for light to reach the earth from the surface of the sun. This also means that the sun we see every day is the same as it was 8 minutes and 20 seconds ago. If the sun suddenly disappears at this moment, the scene when it disappears will not be visible from the earth until 8 minutes and 20 seconds later. By then, the earth will A completely dark moment.
Image source: NASA official website Intrusion and deletion
This is also true in daily life. When an object is one meter away, we see it as it was before, just at this time interval. It will be very short, and the time it takes for the speed of light to fly one meter is still negligible. So what we see is the past, and scientifically speaking, "looking into the future" is impossible.
Article/Science Black Hole, picture source is network intrusion and deletion.