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The Brightest Stars In The Night Sky
Updated: Oct 9, 2021
~ Htoo Myat Noe
The Milky Way is home to billions of stars, those glowing little pearlescent blobs that seem to cast their glow upon us when we gaze up at the night sky to behold the tranquility that the darkness of night offers us. Depending on the location we are at, all of us on our blue marble will view the same night sky differently. In the cities, where light pollution is abundant, starlight in the night sky is unfortunately washed out by the obtrusive, excessive and artificial lighting from the city lights, and people are thus unable to view the vast expanse of glory hidden from view. This is in stark contrast to the open fields and deserts which are isolated from the city lights and are sparsely populated, therefore serving as ideal environments for stargazing. However, despite the light pollution in cities, many of us can still make out some of the brightest stars in the night sky with our naked eye. So what are you waiting for? Let’s find out more about them!
Sirius, also called Alpha Canis Majoris or the Dog Star, is the brightest star in the night sky, with an apparent visual magnitude of −1.46 and an absolute magnitude of +1.4. Sirius is a binary star in the constellation Canis Major. The bright component of the binary is a blue-white star 25.4 times as luminous as the Sun. It has a radius 1.71 times that of the Sun and a surface temperature of 9,940 kelvins (K), which is more than 4,000 K higher than that of the Sun. Its distance from the solar system is 8.6 light-years, only twice the distance of the nearest known star system beyond the Sun, the Alpha Centauri system. Its name comes from a Greek word meaning “sparkling” or “scorching.” (Sirius, n.d.) A sparkling beauty to behold, indeed.
Second to the title of “The brightest star in the night sky” is Canopus, also called Alpha Carinae, with an apparent visual magnitude of −0.73 and an absolute magnitude of -2.5. Canopus is a supergiant of spectral type F and appears essentially white to the naked eye. Lying in the southern constellation Carina, 310 light-years from Earth, Canopus is sometimes used as a guide in the attitude control of spacecraft because of its angular distance from the Sun and the contrast of its brightness among nearby celestial objects. (Canopus, n.d.)
At this point, you may be wondering, what is a star’s apparent magnitude and absolute magnitude? A star’s apparent magnitude is defined by astronomers as how bright the star appears from Earth, and absolute magnitude refers to how bright the star appears at a standard distance of 32.6 light-years, or 10 parsecs, away. (Howell, 2017) The scale for absolute magnitude is the same as that for apparent magnitude, whereby a difference of 1 magnitude = 2.512 times difference in brightness. The lower or more negative the value of magnitude, the brighter the star is. (AglsAgent et al., n.d.) Now, you might be wondering again, why does Sirius have a lower apparent magnitude, thus appearing brighter to us on Earth, but have a higher absolute magnitude than Canopus? Sirius is much closer to us than Canopus, therefore, although it is not actually as bright as Canopus (i.e. not as bright when viewed from a standard distance of 10 parsecs), Sirius appears brighter simply because it is much closer to us as compared to Canopus.
Rigel Kentaurus claims the title of being the third brightest star in the night sky, but its brightness is due to the proximity of the system, commonly known as Alpha Centauri, which is the Sun’s closest star system neighbor, about 4.3 light-years away from Earth. Rigel Kentaurus is part of a triple star system, but we only see a double star with our naked eye. Its two stars are dwarfs that spin around each other every 80 years at an average distance of 23 Earth-sun distances, or astronomical units (AU).
Now, many of you may be wondering, are the stars that I mentioned above the brightest ones in our galaxy, or are they only the brightest as we view them from Earth? The brightness of a star as we view it from our planet depends on the distance between Earth and the star, and the absolute magnitude of said star. Essentially, the distance between the earth and a star and the star’s absolute magnitude both co-affect the apparent magnitude of the star. Hence, to answer, the stars mentioned in this article are only the brightest in the night sky of Earth. There are still many stars out there in our Milky Way that have much lower absolute magnitudes than Sirius, but since they are many more light years away from Earth than Sirius, their apparent magnitudes are higher, and they appear dimmer than Sirius when viewed from Earth. An example of such a star would be Deneb, more than 1500 light years away from the Sun, which despite having a much lower absolute magnitude of -8.73 than the stars mentioned above, has a much higher apparent magnitude of 1.25 because of its huge distance away from the Earth, thus, appearing dimmer to us here on earth.
There are also a plethora of ways to classify stars based on their luminosities and temperatures, besides the absolute and apparent magnitude scales. Many astrophysicists and astronomers over the years have come up with the stellar classification scheme, which is a scheme for assigning stars to types according to their temperatures as estimated from their spectra. The generally accepted system of stellar classification is a combination of two classification schemes, the Harvard system, which is based on the star’s surface temperature, and the MK system, which is based on the star’s luminosity. The types are now arranged in a non alphabetic sequence to put them in order by surface temperature. From hot stars to cool, the order of stellar types is: O, B, A, F, G, K, M. (A traditional mnemonic for this sequence is “Oh Be A Fine Girl [or Guy], Kiss Me.”) (O-Type Star, n.d.) Extensive research is still currently being done to glean more knowledge regarding the most luminous and hottest stars in the Milky Way; a great leap towards getting to understand our universe better.
Picture of the stellar classification scheme from: https://www.britannica.com/science/O-type-star
So where exactly can one go to get the best glimpse of the vast unknown? Astro-tourism, which refers to visiting dark sky reserves that have high visibility and minimal air and light pollution to view, has been an increasingly common branch of tourism over the years. A few examples of such places are Tende, France, Death Valley National Park, California, the Sahara Desert and Banff National Park, Canada. (Gall, 2019)
The Milky Way as seen from Tende, France
Stars have no doubt been celestial masses of fascination for the young ones around the globe, curious to learn more about the world that lies beyond our skies, but as we grow up and the mundanities of life plague our natural instinct to always wonder, we tend to under-appreciate The Great Unknown. So I urge you, if you were to take away only one lesson from this piece, it is to be ever-seeking, ever-searching of the lights that shine above. As Stephen Hawking put it b
“Remember to look up at the stars and not down at your feet. Try to make sense of what you see and wonder about what makes the universe exist. Be curious.”