Exploring the Dimmest Stars: A Look into Faint and Brown Dwarfs Visible to the Naked Eye

Exploring the Dimmest Stars: A Look into Faint and Brown Dwarfs Visible to the Naked Eye

The sun is the brightest and most luminous thing on the planet. It also has the honor of being the closest star to the earth. Although it is a low status on the cosmic level. The Sun is brighter than 85% of the stars in the Milky Way. The phase which Sun is passing through at this time is called Main Sequence phase. Most of the stars in the universe are passing through this phase of their life. The Sun is increasing its brightness by 1% every 10 million years. With so many stars in the universe, it's not surprising that there are stars that are smaller, brighter, and fainter than the Sun. For example, BETELGEUSE, which is in the constellation Orion, is 14,000 times brighter than the Sun. and 61Cygni AB in the Cygnus constellation. It is the faintest star in the sky visible to the naked eye. 

Magnitude scale is used to measure the brightness of stars. It also has two types

1. Apparent magnitude
2. Absolute magnitude

1. Apparent magnitude: It depends on how bright the star appears from Earth. This scale does not reflect the true brightness of the star. Distance and interstellar dust directly affect the brightness of celestial bodies.

2. Absolute Magnitude: This scale measures the brightness of a celestial body at a fixed distance (which is 10 parsecs). 10 parsecs consists of 5.32 light years.

When amateur astronomers look at the sky, they only focus on how bright one celestial body is compared to another. That is, they only consider the external intensity, and Professional astronomers are interested in the true brightness of a star. That is, which of the two objects at the same distance appears brighter. In their view, absolute intensity is more important.

In this article we are studying stars whose absolute magnitude is less than that of the Sun and which are visible to the naked eye. The stars whose absolute magnitude is less than that of the Sun are called faint stars. These stars are brown in color and much smaller than a normal star, so they are also called brown dwarfs. When they are at their hottest, they look reddish-orange. And in a relatively cool condition, they are seen in a magenta color. Brown dwarfs are also evidence that star formation does not always result in a conventional star. Since brown dwarfs are not very large (but much larger than a planet), their cores are not hot enough to trigger nuclear fusion. Therefore, they are very difficult to detect even with the most sensitive telescopes. They are detected in infrared wavelengths. But distinguishing them from other low-mass stars is still a difficult step.

The honor of the first discovered brown dwarf goes to Glaze 229b. It was discovered in 1994 and its location in the constellation Lepus was confirmed in 1995. Luhman 16A is the closest faint star to Earth (5.6 light-years away) of the Luhman 16 system in the constellation Vela. The faintest known brown dwarf, 2mass jo9393548, is the 5th closest faint star, 17 light-years from Earth. This star in the constellation Antlia is a million times dimmer than our Sun.

The Milky Way is a billion times fainter than the Sun in the visible spectrum, along with another brown dwarf. We can see 9000 stars with an apparent magnitude of 0.6 with the naked eye. The absolute magnitude of our Sun is 83.4, which means that after 10 parsecs, we will be able to see the Sun shining with an apparent magnitude of 83.4. Interestingly, out of these 9000 stars, only 42 stars have an absolute magnitude less than the Sun. And a star that is dimmer than the Sun must be very bright or very close to be visible with or without binoculars. And there are quite a few stars within 10 prisms of Earth. Only 5% of the 9000 stars are within this distance. Because, The remaining 95% of stars are far from this limit and are still visible, so it is obvious that they are brighter than the Sun.

The 10 faintest stars in the night sky are those less bright than the Sun in absolute magnitude and brighter than 5.6 in apparent magnitude and can be seen with the naked eye:

Number: 1

Name: Epsilon Eridani

Constellation: Eridanus

Coordinates: (03h 32m 56s) + (+09° 27′ 30″) 

(RA/Dec): App: 3.7

Magnitude: Abs: 6.2

Significance: Epsilon Eridani is a star in the constellation Eridanus, about 10.5 light years away from Earth. It's a young star that's similar in mass and size to the Sun, but much cooler and less luminous. It's also known to have at least one exoplanet orbiting it. The third faintest star closest to Earth.

Number: 2
Name: 61 Cygni AB
Constellation: Cygnus
Coordinates: (21h 06m 55s) + (+38° 44′ 41″)
(RA/Dec): App: 4.8
Magnitude: Abs: 8.3

Significance: 61 Cygni AB is a binary star system in the constellation Cygnus, about 11.4 light years away from Earth. The two stars are both dim and cool, with a combined mass of about 1/5 that of the Sun. They were the first stars to have their distances measured through the technique of stellar parallax. The faintest star visible to the naked eye with absolute magnitude.  

Number: 3 
Name: Epsilon Indi 
Constellation: Indus
Coordinates: (22h 03m 22s) + (-56° 47′ 10″)
(RA/Dec): App: 4.8
Magnitude: Abs: 6.9

Significance: Epsilon Indi is a triple star system in the constellation Indus, about 11.8 light years away from Earth. The primary star is a cool, orange-red dwarf, while the two companion stars are smaller, cooler brown dwarfs. Epsilon Indi is one of the closest star systems to our own. An orange colored dim star surrounded by two brown ones which are also Kamadhams.

Number: 4
Name: Tau Ceti
Constellation: Seats
Coordinates: (01h 44m 04s) + (-15° 56′ 15″)
(RA/Dec): App: 3.5
Magnitude: Abs: 5.7
Significance: Tau Ceti is a star in the constellation Cetus, about 11.9 light years away from Earth. It's similar in mass and size to the Sun, but much older and less active. It's also known to have at least four exoplanets orbiting it.The brightest of the dim stars, resembling the Sun in its spectrum and is less luminous than the Sun in absolute magnitude.


Number: 5
Name: 85 Pegasi
Constellation: Pegasus
Coordinates: (00h 02m 10s) + (+27° 04′ 56″) 
(RA/Dec): App: 6.4
Magnitude: Abs: 5.3

Significance: 85 Pegasi is a star in the constellation Pegasus, about 33.7 light years away from Earth. It's a relatively bright star that's visible to the naked eye under good viewing conditions. It's also known to have at least one exoplanet orbiting it. You are visible from the naked candidate in dark and clear weather (free of light and atmosphere).

Number: 6
Name: Sigma Draconis 
Constellation: Draco
Coordinates: (19h 32m 22s) + (+69° 39′ 40”) 
(RA/Dec): App: 4.7 
Magnitude: Abs: 5.9 

Significance: Sigma Draconis is a star in the constellation Draco, about 18.8 light years away from Earth. It's a bright star that's similar in mass and size to the Sun, but much older and less active. It looks surprisingly bright enough to be less bright than the Sun.

Number: 7
Name: 70 Ophiuchus 
Constellation: Ophiuchus
Coordinates: (18h 05m 27s) + (+02° 29′ 00”)
(RA/Dec): App: 6.1
Magnitude: Abs: 5.5

Significance: 70 Ophiuchi is a binary star system in the constellation Ophiuchus, about 16.6 light years away from Earth. The two stars are both relatively faint and cool, with a combined mass of about 1/3 that of the Sun. The primary star is also known to be variable in brightness. A variable but very faint star visible to the naked eye on a dark night.

Number: 8
Name: Mu Cassiopeiae
Constellation: Cassiopeia
Coordinates: (01h 08m 16s) + (+54° 55′ 13”)
(RA/Dec): App: 5.2
Magnitude: Abs: 5.8

Significance: Mu Cassiopeiae is a star in the constellation Cassiopeia, about 54.2 light years away from Earth. It's a relatively bright star that's part of a multiple star system, with three other stars in close proximity. Accompanied by its three companion stars in the Milky Way.

Number: 9 
Name: 61 Ursae Majoris
Constellation: Ursa Major
Coordinates: (11h 41m 03s) + (+34° 12′ 06”)
(RA/Dec): App: 5.4
Magnitude: Abs: 5.5

Significance: 61 Ursae Majoris is a star in the constellation Ursa Major, about 31.1 light years away from Earth. It's a relatively bright star that's similar in mass and size to the Sun, but much older and less active. A yellow-orange star that is part of the circumpolar constellation.

Number: 10 
Name: 54 Piscium
Constellation: Pisces
Coordinates: (00h 39m 22s) + (+21° 15′ 02”) 
(RA/Dec): App: 5.9
Magnitude: Abs: 5.7

Significance: 54 Piscium is a star in the constellation Pisces, about 36.1 light years away from Earth. It's a relatively dim star that's orbited by a planet and a brown dwarf, making it an interesting target for exoplanet research.

These dim stars are difficult to spot due to their faintness and often go unnoticed by amateur stargazers. But for professional astronomers, they offer valuable insights into the formation and evolution of stars.

The faintest star visible to the naked eye is 61Cygni AB, with an absolute magnitude of 6.03. It is located in the Cygnus constellation and appears as a dim, orange-colored star. Other faint stars include Groombridge 1830, Lacaille 8760, and Wolf 359, all of which are within 10 parsecs of Earth.

Despite their dimness, these stars play an important role in our understanding of the universe. They offer clues about the processes that lead to the formation of stars, and their properties can help astronomers refine their models of stellar evolution.

So the next time you look up at the night sky, take a moment to appreciate the dimmest stars that twinkle in the darkness. They may be faint, but they shine a light on some of the most fascinating phenomena in the universe.