The Sun is the brightest object in our solar system, but that’s because it is the closest to us. In fact, it is a medium-sized star whose brightness is quite average compared to other stars in the cosmic neighborhood.
A star’s brightness in our sky depends on how far away it is from us, its chemical composition, and how big it is.
There are some pretty extreme examples out there. For example, Betelgeuse, in the constellation of Orion, shines with a luminosity a whopping 14,000 times brighter than our Sun!
Given these variables, how do astronomers determine brightness for stars? And, can we see some of those extreme stars in our night skies?
Let’s find out.
How Do We Measure the Brightness of Stars?
Quick Answer: We measure the brightness of stars using absolute and apparent magnitudes.
Magnitude is a strange and non-intuitive measurement. We’ll provide a quick summary here, but we have also written a detailed guide to stellar magnitude that you might want to check out.
The lower the magnitude, the brighter an object is. Magnitude is measured on a logarithmic scale where a 5 points increase equates to a ‘shine’ that is 100 times dimmer.
For example, a star shining at magnitude 5.0 is 100 times dimmer than a star of magnitude 0.0.
Magnitudes can be negative numbers. Any object with a negative magnitude is brighter than one with a positive magnitude. Our Sun is the brightest object in our sky by some considerable margin and shines at magnitude -26.7.
Apparent and Absolute Magnitude
Consider the Moon: it is the brightest object in our night sky. But if the Moon were farther away, it would seem a little less bright. If there was a lot of fog in front of the Moon, it would seem even dimmer.
The same concept applies in outer space as well. Stars are very far away from us, and space is not empty so some of their light can be blocked by interstellar dust, for example.
Astronomers use apparent magnitude to measure the brightness of stars as we see them from Earth. The lower the number, the brighter the object.
Apparent magnitude tells us how bright the star ‘appears’ to be, not how bright it really is.
Absolute magnitude is also a logarithmic measurement that measures the brightness of stars at a fixed distance of 10 parsecs or 33 light-years. This allows scientists to compare the intrinsic brightness of stars, which is how we can say Betelgeuse is brighter than the Sun, even though it’s much fainter in our sky than the Sun is.
In this article, we’ll be determining the ‘brightest stars’ based on their apparent magnitude, i.e. how bright they appear in the night sky.
What is the Brightest Star?
Quick Answer: The brightest star in the night sky is Sirius [A&B] at magnitude -1.46. It is also called Alpha Canis Majoris, and is commonly known as the Dog Star. It resides in the constellation of Canis Major.
Sirius is 8.6 light-years away from us, close enough to be the brightest star in our night skies.
However, as bright as it is, its apparent magnitude of -1.46 makes it over 12 million times dimmer than our Sun.
Sirius is part of the Canis Major constellation, also called the Greater Dog. This inspired the Dog Star nickname, as well as ‘The Pup’ for its much dimmer companion star.
When seen from Earth, Sirius exudes different colors (partly due to Earth’s layered atmosphere), and some actually mistook the star to be a UFO!
From both northern and southern hemispheres, Sirius rises in the northeast and sets in the northwest (it rises mid-evening come December).
It is easy to locate due to the fact it is the brightest star in the night sky. You can also find it by drawing a line extending Orion’s belt downward (to the left), as shown in the image from SkySafari 6 below.
Sirius is only 225 to 250 million years old, which means that it has orbited the galaxy only once.
- Absolute Magnitude: +1.4
- Apparent Magnitude: -1.46
- Size Compared to the Sun: Less than twice the Sun’s diameter
- Age: 225 to 250 million years old (The Sun is 20 times older)
- Life expectancy: 1 billion years for Sirius. The Pup is already a dead star (white dwarf).
- Constellation: Canis Major the Greater Dog
- Coordinates: R.A. 06h 45m 09s, Dec -16° 42′ 58″
The Brightest Stars in the Night Sky
The table below shows some of the most significant bright stars in order of apparent brightness. Below the table, we’ll look at each one in more detail.
|Sirius||-1.44||Brightest star in the night sky|
|Canopus||-0.62||2nd brightest star in the sky, brightest in the southern hemisphere|
|Alpha Centauri||-0.27||3rd brightest star in the night sky and brightest in the Centaurus constellation|
|Arcturus||-0.15||4th brightest star in the night sky and brightest in Bootes constellation. Brightest in the northern hemisphere|
|Vega||+0.02||Brightest in Lyra. 2nd brightest in the northern hemisphere|
|Capella||+0.07||6th brightest star in the night sky and 3rd brightest in the northern hemisphere|
|Rigel||+0.28||Brightest in Orion constellation|
|Procyon||+0.40||8th brightest star in the night sky and brightest in Canis Major constellation|
|Achernar||+0.54||9th brightest star in the night sky and brightest in the Eridanus constellation|
|Betelgeuse||+0.56||3rd brightest in Orion constellation after Rigel|
|Hadar||+0.63||2nd brightest in Centaurus constellation after Alpha Centauri|
The star Canopus is the second-brightest in the night sky and the brightest in the southern hemisphere. It shines at magnitude -0.64.
It is part of the constellation of Carina, which is not visible at all from the northern hemisphere locations north of 37°N, so it can only be observed from southern US states. In Europe, it can only be seen from Malta and the southern tips of Spain and Greece.
It is only 310 light-years from the Sun and is a bright white giant, over 10,000 times brighter than our home star.
- Absolute Magnitude: -5.50
- Apparent Magnitude: -0.62
- Size Compared to the Sun: 71 times larger
- Age: 30 million years
- Life Expectancy: Unknown
- Constellation: Carina
- Coordinates: R.A. 06h 23m 57s, Declination -52° 41’ 44”
Alpha Centauri is the third brightest star(s) in the night sky and the brightest in its constellation Centaurus. Due to its position, viewers in the northern hemisphere need to be further south than 28 degrees latitude to see it.
4.37 light-years away, Alpha Centauri is the closest known star system to Earth. The system consists of 3 stars, two of which are Sun-like and are close enough to appear as one point of light when seen from Earth.
The star system is found at the bottom of its constellation Centaurus, which is a southern hemisphere constellation.
The biggest star has a yellow A component and an orange B component which are 6″ apart and easily separated in a telescope. A is 1.5 times brighter than the Sun while B is 0.4 times brighter. The red dwarf C component is the closest star to Earth but only shines at magnitude 11.
A and B have a fairly elliptical orbit, and the distance between them changes over an 80 year orbital period from 35.6 AU (roughly equal to the distance between the Sun and Pluto) to 11.2 AU (roughly equal to the distance between the Sun and Saturn).
- Absolute Magnitude: 4.34 is the total system’s brightness
- Apparent Magnitude: -0.27 overall. A is -0.01 (the brightest), B is 1.3 and C is 11 (the dimmest)
- Size Compared to the Sun: The diameter of A is 20% bigger than the Sun’s, B is 14% smaller, and C is 85% smaller than our star.
- Age: The stars of Alpha Centauri are between 5 and 6 billion years old, which is 1 billion years older than the Sun
- Life expectancy: Unknown for Alpha Centauri A and B. C is expected to live 1 trillion years after the other two cease living
- Constellation: Centaurus (the half man, half horse)
- Coordinates: AB system: R.A. 14h 39m 37s, Dec -60° 50′ 02″
- Coordinates: Proxima Centauri: R.A 14h 29m 43s, Dec -62° 40′ 46″
Arcturus is probably as close as we can get to seeing a star that’s close to its death. 36.7 light-years away from Earth, Arcturus is a variable star that’s already exhausted the hydrogen in its core.
Because it no longer has hydrogen for fusion, the star is beginning to contract, thereby increasing its core temperature. This ignites the burning of a hydrogen shell and is called the hydrogen shell burning phase.
Because Arcturus is nearing its end, it has expanded to 25 times the Sun’s diameter, and will slowly contract into a white dwarf in the next 1 billion years. Before that, it will make its closest approach to the Sun in the next 4,000 years.
You can find Arcturus with the help of Big Dipper. Follow the arc from its panhandle to the bright orange star at the bottom of the ‘kite’ of Boötes constellation.
- Absolute Magnitude: -0.30
- Apparent Magnitude: -0.15
- Size Compared to the Sun: 25 times the Sun’s diameter
- Age: 7.1 billion years
- Life expectancy: 8.5 billion years
- Constellation: Boötes the Herdsman
- Coordinates: R.A. 14h 15m 40s, Dec +19° 10′ 57″
At magnitude 0.3, Vega is the brightest star in its constellation Lyra. It is 25 light-years away from us and reaching the midpoint of its life. You can see it as a blueish circumpolar star, often near the Zenith above 51° N latitudes.
To see it, you only need to look up near the easier-to-find constellation of Cygnus the swan. It is the second brightest star in the northern hemisphere.
- Absolute Magnitude: +0.58
- Apparent Magnitude: +0.02
- Size Compared to the Sun: 2.5 times the Sun
- Age: 455.3 million years old
- Life expectancy: 1 billion years
- Constellation: Lyra the Harp
- Coordinates: R.A. 18h 36m 56s, Dec +38° 47′ 01″
We’ve encountered star systems made of one and two stars. Let’s tackle a four-star system with Capella. 42.2 light-years away from us, Capella is the brightest yellow star (the same wavelength as our Sun) in the night sky.
It is made up of two sets of binary systems. The first system is called Capella A and its stars are called Capella Aa and Ab.
The two stars are type G like our Sun but they have exhausted their hydrogen supply and are well on their way to becoming red giants.
They are currently 5 times their original size and 80 times brighter than the Sun. This is surprising when we learn that the system is only 400 million years old (the Sun is 4 billion years old and still going strong).
Capella A system is 2.5 times massive than the Sun and is thus exhausting its fuel rapidly.
The second binary system is about 10,000 AU from Capella A. The two stars in the second system are called Capella C and D, or Capella Ha and Hb. They have a combined magnitude of 1% of the Sun, so they aren’t visible with a naked eye.
The combined Capella system made its closest approach to our solar system 237,000 years ago, during which its brightness increased to -0.76 from its usual 0.07.
Capella is not seen south of 44° S and becomes circumpolar for observers north of 44° N. It can be found by drawing a straight line through Megrez and Dubhe in Ursa Major, as shown in the SkySafari 6 image below.
- Absolute Magnitude: -0.48
- Capella Aa: 0.35, Ab: 0.20, Ha: 9.53, Hb: 13.0
- Apparent Magnitude: +0.07
- Capella Aa: 0.91, Ab: 0.76, Ha: 10.16, Hb: 13.7
- Size Compared to the Sun: Capella Aa is 12 times larger than the Sun, Capella Ab is nine times bigger
- Age: 400 million years
- Life expectancy: Nearing the end of their life cycle, will become red giants in the next few hundred years
- Constellation: Auriga the Charioteer
- Capella A: R.A. 05h 16m 41s, Dec +45° 59’ 53”
- Capella H: R.A. 05h 17m 24s, Dec +45° 50’ 23”
The bright star Rigel is another multiple star system with at least four known stars. Rigel, which in Arabic means ‘heel’, is found at the bottom of the Orion constellation, as shown below.
Rigel’s stars all appear as a single bluish-white star to the naked eye. They are 860 light-years away from us and shine between 61,500 and 363,000 times brighter than our Sun! This makes Rigel the brightest star in Orion and the 7th brightest in the night sky.
This star system has exhausted its hydrogen, expanded, and already cooled into a supergiant.
Its unstable atmosphere is still causing it to lose mass at a rate of 10 million times faster than the Sun. In just a few thousand years, Rigel will end its life as a type II supernova and dissolve into either a neutron star or a black hole. View it while you can.
- Absolute Magnitude: 0.12
- Apparent Magnitude: +0.28
- Size Compared to the Sun: Rigel is 70 times the Sun’s radius
- Age: 7 to 9 million years
- Life expectancy: Unknown, but short
- Constellation: Orion the Hunter
- Coordinates: R.A. 05h 14m 32s, Dec -08° 12’ 06”
The 8th brightest star in the night sky and the brightest in Canis Major, Procyon is a binary star system 11.46 light-years away. The bigger and brighter star, Procyon A, is currently a subgiant shining 7 times brighter than the Sun.
It is expanding into a red giant as it ages and will eventually end up 80 to 150 times larger than its current diameter. This is not a fast process, taking between 10 and 100 million years. Its companion star, Procyon B, ended its life by becoming a white dwarf star over one billion years ago.
The star system can be seen as one of the 3 stars forming the Winter Triangle Asterism. The other two stars are Sirius and Betelgeuse, as shown in the SkySafari 6 image below.
- Absolute Magnitude: Procyon A 2.66, Procyon B 13.0
- Apparent Magnitude: +0.40
- Procyon A: 0.34, Procyon B: 10.7
- Size Compared to the Sun: Procyon A is twice the Sun’s size
- Age: Procyon A 1.85 billion years, Procyon B, 1.37 billion years
- Life expectancy: Procyon A >10 million years. Procyon B stopped fusion reactions over one billion years ago
- Constellation: Canis Major the Little Dog
- Coordinates: R.A. 07h 39m 18s, Dec +05° 13’ 30”
Achernar is the 9th brightest star in the night sky and the brightest in its constellation Eridanus. It is 144 light-years away and shines 3.1 times brighter than our Sun. However, it is a southern star and can’t be seen further north than 33° N.
Achernar is spinning at a rapid pace of 250 km or 150 miles per second, a rate that causes its equator to be 50% bigger than its poles.
- Absolute Magnitude: -1.46
- Apparent Magnitude: 0.54
- Size Compared to the Sun: 10 times larger than the Sun
- Age: 37.3 million years
- Life Expectancy: 100 to 500 million years
- Constellation: Eridanus
- Coordinates: R.A. 01h 37m 43s, Dec -57° 14’ 12”
Betelgeuse is the 10th brightest star in the night sky and the second brightest in Orion (Rigel is the brightest). It is over 100,000 times brighter than the Sun and around 800 times larger.
Betelgeuse is 640 light-years away and easy to spot because on the eastern shoulder of Orion the Hunter. It is also noticeable due to its deep reddish color, as shown in the image below from SkySafari 6.
There was speculation in late 2019 that the star was about to go supernova because of the red giant’s age and the sudden dimming it experienced. Now, however, astronomers think the dimming was caused by a release of gas that hid some of the light from Betelgeuse from our line of sight.
- Absolute Magnitude: -5.85
- Apparent Magnitude: +0.56
- Size Compared to the Sun: Over 800 times larger than the Sun
- Age: 8 to 8.5 million years
- Life Expectancy: 0-10 million years
- Constellation: Orion the Hunter
- Coordinates: R.A. 05h 55m 10s, Dec +07° 24’ 26”
Hadar is the second brightest star in Centaurus constellation and the 10th brightest in the night sky. It is a triple-star system, but at 390 light-years away, the individual stars are indistinguishable without proper equipment.
Hadar is also called Beta Centauri, more commonly known as Agena (derived from the Latin word ‘genua’, meaning ‘knees’). Beta Centauri forms the left knee of the Centaur. A line drawn from Beta Centauri and Alpha Centauri directs a viewer to the south celestial pole, which is why the two systems are called ‘southern pointers’.
Because Beta Centauri is primarily seen in the southern hemisphere (it is circumpolar here), it is below the horizon for viewers north of 30° N.
- Absolute Magnitude: -4.53
- Apparent Magnitude: 0.63
- Size Compared to the Sun: 13 times the Sun’s radius
- Age: 14.1 million years
- Life Expectancy: Unknown, but suspected to be short
- Constellation: Centaurus
- Coordinates: R.A. 14h 03m 49s, Dec -60° 22’ 23”
The stars in our universe are immensely diverse in their sizes, colors, and brightness. The way we rank the brightest stars, using apparent magnitude, shows which appear brightest from Earth, not the actual brightest stars in the sky.
All of the star systems on our list are visible with the naked eye, and many of them have companion stars which viewed with a small telescope.
Would you like to look up in the night sky to try and see if you can find them?