How far away do you need to be from the Earth in the optical range to be invisible?

It is known that the Voyager 1 spacecraft, at a distance of 6 billion kilometers from Earth, can only be seen by magnification. This is currently the farthest distance at which the Earth can theoretically be seen. Whether it is far away depends on the development of science and technology.

Theoretically, it can be seen no matter how far away it is, because the light of the earth does not dissipate. However, due to the actual resolution of the camera, it is impossible to see at a long distance. Voyager 1 still photographed the Earth at a distance of 6 billion kilometers, even though it was as small as a dot, the farthest known distance.

In February 1990, the Voyager 1 space probe photographed a very small spot of light from Earth in the orbit of Saturn. After leaving Saturn, Voyager 1 will not be able to find Earth in the universe.

If the speed of light is equal to the speed of light, then all the stars in the universe that humans see are already the same as those of stars many billions of years ago, so it is unknown whether they have changed.

The farthest planet that the human eye can see is 7.5 billion light-years from Earth, and this planet is GRB 080319b.

Less than a light year, the limit of human vision is less than 30 kilometers, and the speed of light is so fast that it is not necessary to calculate in light years.

Thanks to Goku for the invitation. Seeing this question, a sentence suddenly came to mind"Look up, and you'll see farther in the dark"。It is said that the human eye (excluding my myopic eye, of course) can see a distance of 16 to 27 kilometers on a clear sea.

If we want to see further, we can"If you want to be poor, go to the next level"。But no matter how far you look, you can't see far away in the night sky! When we look up at the stars, you see the moon 384,000 kilometers away from us; We see the nearest Venus more than 40 million kilometers away from us.

If you see Saturn, you're seeing 100 million kilometers away. However, the only stars visible to the naked eye in the sky are the Moon, Mercury, Venus, Mars, Jupiter, and Saturn. Most of the stars are stellar and very far away from us.

The distance in kilometers is too far. This is calculated in light years. How far is a light year?

A light-year refers to the distance traveled by light in a year. A light-year is about 9460730472580 kilometers. With light-years, we can measure the farther stars we see.

For example, bright Sirius is light-years away from us; Vega is 25 light-years away; Polaris is 434 light-years away. See the red Betelgeuse on Orion's right shoulder? Seeing it, our eyes can see 640 light-years away.

Most of the stars we can see with the naked eye are hundreds of light-years away. Can our eyes see objects farther away? On a clear night, in the northeastern part of the sky, you will see an oval spot that looks like a spindle.

This is the Andromeda Galaxy.

It is a galaxy larger than our Milky Way, located 2.54 million light-years from Earth. The Andromeda Galaxy is one of the most distant celestial objects visible to the naked eye. Of course, Andromeda is not the farthest celestial body visible to the naked eye.

The farthest celestial bodies visible to the naked eye are triangular galaxies. It's about 2.9 million light-years away from us. This is basically the limit of what we humans can see with the naked eye.

However, the farthest object in history that can be observed by the human eye is the GRB 080319B gamma-ray burst on March 19, 2008, which is 7.5 billion light-years away from Earth! It is also the farthest celestial body that can be seen by the human eye.

Most of the stars visible to the naked eye are not more than 1,000 light-years away from the Earth, and the stars we are familiar with, such as Sirius, Arcturus, Vega, and Cowherd, are only a few dozen light-years away from the Earth, and in 2008, gamma-ray bursts reached the Earth at the speed of light after a long journey of 7.5 billion years, and their brightness was so high that it was visible to the naked eye for half a minute.

How far can our eyes see celestial bodies farther away? On a clear night, in the northeast of the sky you will see an oval spot that looks like a spindle. This is the Andromeda Galaxy.

It is a galaxy larger than our Milky Way, located 2.54 million light-years away from Earth. The Andromeda Galaxy is one of the most distant celestial objects visible to our human eyes.

Of course, the Andromeda galaxy is not yet the farthest object visible to the naked eye. The farthest visible object to the naked eye is the Triangulum Galaxy. It's about 2.9 million light-years away.

This is basically the limit of what we humans can see with the naked eye. However, the farthest object ever observed by the human eye in history was a gamma-ray burst of GRB 080319b on March 19, 2008, 7.5 billion light-years away from Earth!

The nearest is about 26 light-years and the farthest is about 100 light-years, and there are a total of 300 million planets in the Milky Way, some of which are 30 light-years away from Earth, because scientists have responded to this aspect.

Scientists have calculated that there are more than 6,000 stars in the night sky that can be directly observed with the naked eye, most of which are stars, and they are generally not more than 1,000 light-years away from Earth. So, how far away will the planet be from Earth that our human eyes can see?

When we look up at the starry sky, you see the moon 384,000 kilometers away from us; The closest Venus we see is more than 40 million kilometers away. If you see Saturn, you're 100 million kilometers away. However, the only stars in the sky are the Moon, Mercury, Venus, Mars, Jupiter and Saturn, and most of the stars are stars and are very far away from us.

It's so far away that you can't calculate the distance in kilometers anymore, it's going to take light years.

I've seen relevant information on the vegetable leaf network before, due to the physiological structure of the human eye, there is a certain limit to visible objects. Most of the stars visible to the naked eye are not more than 1,000 light-years away from Earth. However, because everyone's eyesight is different, and many high-brightness stars are deformed, some stars as far away as 10,000 light-years may also be visible to the naked eye under very good observation conditions, such as:

1) HD91619 star in the constellation Cygnus, apparent magnitude, 10,000 light-years from Earth;

2) HD188001 star in the constellation Sagittarius, apparent magnitude, 10,000 light-years from Earth;

3) Cygnus HD188209 star, apparent magnitude, 10,000 light-years from Earth.

Some of the stars we see in the night sky are not individual stars, but distant galaxies, and because they are so far away, the light emitted by the massive stars in those galaxies forms a "combination" that can be seen by the human eye on Earth, or a faint bright spot.

For cosmic objects, whether we can observe them on Earth depends mainly on the above two factors, and some other factors, such as weather conditions, cloud thickness, air pollution levels, and light pollution effects, can be avoided to a certain extent by choosing the right time and area.

For stars outside the solar system, the brightness we observe on Earth is closely related to the intensity of their own radiation and their distance from the Earth.

The brightest star we can see is Sirius, which is located further south in China, and in winter, it forms a large winter triangle with Betelgeuse in Orion and Nanhe III in Canis Minor, which is very conspicuous at night. But Sirius is only light-years away, South-River is about light-years away, and Betelgeuse is about 640 light-years away.

Current theories and observations all show that the universe occurred 137-13.8 billion years ago. In the first few hundred million years of the universe, there was no familiar type of celestial existence (stars, galaxies, clouds), and the universe was in a state of darkness, and naturally there were no celestial bodies that we could directly observe. Of course, we can observe the afterglow of the big **, which is the famous "3K microwave".

Above is the farthest galaxy ever observed (i.e., the galaxy with the largest redshift), which corresponds to a distance of about 13.4 billion light-years. The telescope that photographed this galaxy is the famous Hubble, which has been on this piece of sky without bright stars for two months, and has obtained the above**, and at the same time refreshed mankind's understanding of the galaxy at the beginning of the formation of the universe.

Space limitations, if the landlord is interested, you can click on the link link below.

Scientists can observe with astronomical telescopes; It is also possible to analyze the ** information of telescopes coming from space.

In space, there are devices such as the Hubble Telescope, which are brought by rockets or spaceships to observe more distant galaxies, and can transmit ** information back to space.

This allows scientists to make observations at a distance of billions of light-years from Earth.

Because we're looking at the state of those planets or coefficients hundreds of millions of years ago.

For example, according to the different distances, we can see stars in different periods, so human beings can know the evolution process of stars, in fact, the most primitive stars have long since ceased to exist, but because some are far away from us, its light traveled hundreds of millions of years to the earth, and we saw what it looked like hundreds of millions of years ago.

Based on this, scientists have speculated on the age of the universe, but if we see stars that do not travel to Earth within the age of the universe, we can prove that the speculation is wrong, but it has not been observed that far.