What is the farthest star we can see with the naked eye? – 09/01/2022

Determining the most distant star that we can see in the sky without the help of equipment may seem like a simple task. But there are so many variables, such as the state of the night sky, imprecise distance calculations, or whether we’re talking about single stars, that we end up finding many answers to this very question.

to get an idea, tilt Three astronomers consulted to try to answer the question, and each named a different star.

What we do know is that, under ideal conditions, the human eye can see objects of apparent magnitude 6 (a measure of the brightness of a star from Earth). The lower the number, the brighter the object. The Sun, for example, has a magnitude of -26.

If we take into account the real possibilities of observing in a polluted sky, like any large city, the most distant star we can see is Deneb, in the constellation Swan.
Alexander Cherman, astronomer at the Rio Planetarium

Tail is a star of apparent magnitude 1.25 and is included in the list of the 20 brightest in Earth’s sky.

According to estimates, it is more than 2,000 light years away from Earth, that is, the light it emits takes more than 2,000 years to reach here.

Its radius is about a hundred times that of the Sun, and it is about a hundred thousand times brighter than the Sun.

a clear sky

Now, if we imagine a sky with ideal observing conditions, without pollution and artificial lighting, as in the desert, for example, it is possible to observe a more distant star, V762 Cas, with an apparent magnitude of 5.8.

But the actual distance to the star is very controversial. It is often said to be 16,300 light-years from Earth, but other databases show anywhere from 2,000 to 3,000 light-years away.

The discrepancy occurs because the measurement is done using complex mathematical calculations—which involve Earth’s orbit or comparison with the brightness of other known stars—and very subtle differences in the data lead to very different distances, explains Ruggero Revel, chair of the astronomy department at UFRS (Federal University of Rio Grande). Do Sol).

Two stars in one

There is another possibility: the binary system, when two celestial bodies (such as stars) orbit a common center of mass and are bound by gravity.

An estimated one-third of the Milky Way’s star systems are binary.

If such a system is taken into account, we will get another star in the list of the most distant observable with the naked eye.

It is Eta Carinae, consisting of two stars 150 times more massive than the Sun and located 7,500 light years from Earth. Its apparent size is about 4.4.

“It’s a very giant star, so it’s very bright,” says Roberto Costa, a professor in the University of the South Pacific’s Department of Astronomy.

It should be noted that the brightness of a star is measured not only by its distance from the Earth, but also by its size and temperature.

For example, Sirius is the brightest star in the sky (at night) and is 8.7 light-years away from the Sun. However, it is very far from Alpha Centauri, which is considered the closest star to the Sun (4.2 years). – Light ).

the farthest object

The most distant thing that we can see with the naked eye is the Andromeda galaxy, which is located 2.5 million light-years from Earth.

“Because it is a galaxy as large and luminous as our own, it can be seen with the naked eye,” Costa explains.

Galaxies can be compared to large star-filled cities. Andromeda is a 3.4-magnitude massif, so it can be seen without the need for telescopes.