The Brightest Stars In the Universe Insane Curiosity
There are countless stars that we can see in our night sky, and all of them are unique.
Some are dim such that they are barely visible without a telescope.
Others are bright and can be seen even in the most light-polluted areas.
The brightness of a star depends on its composition and its location relative to our planet.
Astronomers define star brightness in terms of apparent magnitude which is how bright
the star appears from Earth and absolute magnitude which is how the star appears at a standard
distance of 32.6 light years, that is equivalent to 10 parsecs.
In addition to this, astronomers measure a star's luminosity which is the amount of energy
that a star emits from its surface.
Measuring a star’s brightness is an ancient procedure, However, today’s astronomers
use more precise tools and equipment to obtain their measurements.
Curious to know the brightest stars in the sky?
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Passage 1
The brightness of stars is measured using the magnitude scale, which seems a little
backwards.
Since the lower the number, the brighter the object is and the higher the number, the dimmer
it is.
This scale is logarithmic and set so that every 5 steps equals a 100 times decrease
in brightness.
So magnitude 10 is 100 times dimmer than magnitude 5, which in turn is 100 times dimmer than
magnitude 0.
More than 2000 years ago, the greek astronomer Hipparchus was the first to categorize the
stars according to their brightness.
Basically, he looked at the stars in the sky and classified them by how bright they appear.
The brightest stars were of magnitude 1, the next brightest were of magnitude 2 and so
on down to magnitude 6 which were the faintest stars he could observe.
Human eyes, however, are not very discerning since large differences in brightness actually
appear much smaller using this scale.
Therefore, light-sensitive charged coupled devices inside digital cameras measure the
amount of light coming from stars, and can provide a more precise definition of brightness.
Using the scale magnitude, astronomers now define five magnitudes’ difference as having
a brightness ratio of 100.
Vega was used as the reference star for the scale.
Initially, it had a magnitude of 0 but more precise measurements changed that to “0.3
“.
When taking Earth as a reference point, the scale magnitude fails to account for the true
differences in brightness, or apparent magnitude, depending on the location of the observer.
Different observers will come up with a different measurement, depending on their locations
and distance from the star.
Stars that are closer to Earth, but fainter, could appear brighter than far more luminous
ones that are far away.
Therefore, it is useful to establish a convention whereby we can compare two stars on the same
footing, without variations in brightness due to different distances complicating the
issue.
A solution to these variations, was to implement an absolute magnitude scale to provide a reference
between stars.
To do so, astronomers calculate the brightness of stars as they would appear 32.6 light years
or 10 parsecs from Earth.
Another of brightness is luminosity which is defined in the introduction.
It’s usually expressed in watts and measured in terms of the luminosity of the Sun or the
Solar Luminosity which is approximately 3.827 times ten to the power 26 watts -( 3.827*10^26)
watts- and one of the closest stars to Earth, Alpha Centauri A, is about 1.3 times the solar
luminosity.
To figure out luminosity from absolute magnitude, one must calculate that a difference of five
on the absolute magnitude scale is equivalent to a factor of 100 on the luminosity scale
— for instance, a star with an absolute magnitude of 1 is 100 times as luminous as
a star with an absolute magnitude of 6.
While the absolute magnitude scale is astronomers' best effort to compare the brightness of stars,
there are a couple of main limitations that have to do with the instruments that are used
to measure it.
First, astronomers must define which wavelength of light they are using to make the measurement.
Stars can emit radiation in forms ranging from high-energy X-rays to low-energy infrared
radiation.
Depending on the type of star, they could be bright in some of these wavelengths and
dimmer in others.
To address this, scientists must specify which wavelength they are using to make the absolute
magnitude measurements.
Another key limitation is the sensitivity of the instrument used to make the measurement.
In general, as computers have advanced and telescope mirror technology has improved over
the years, measurements that are made in recent years have more weight among scientists than
those that are made long ago.
Paradoxically, the brightest stars are among the least studied by astronomers, but there
is at least one recent effort to catalog their luminosity.
A constellation of satellites called BRITE “BRight Target Explorer” will measure
the variability of brightness between stars.
Participants in the six-satellite project include Austria, Canada and Poland.
The first two satellites launched successfully in 2013.
Passage 2
While many stars have a consistent brightness, there are more than 100,000 known and cataloged
variable stars.
Even our own sun is variable, varying its energy output by about 0.1 percent, or one-thousandth
of its magnitude, during its 11-year solar cycle.
Variable stars are either intrinsic, meaning their luminosity changes due to features such
as expansion, contraction, eruption or pulsation. or extrinsic, meaning that a star or planet
passes in front of the star and blocks the light, or that the change is due to stellar
rotation.
Stars can also change in luminosity over time.
The North Star or Polaris, for example, could have been as much as 4.6 times brighter in
ancient times than it was today.
A 2014 study noted that the star dimmed for the past few decades, but then drastically
brightened again.
Polaris is part of the class of Cepheid variables, which are extremely luminous stars that have
short pulsation periods.
The variations in the luminosity allow astronomers to calculate how far away these Cepheids are,
making them useful "measuring sticks" if the stars are embedded in galaxies or nebulae.
Other types of intrinsic variable stars include cataclysmic variables which brighten due to
outbursts, such as during supernovae explosions or eruptive variables whose brightness varies
during eruptions on the surface, or combinations with interstellar matter.
Extrinsic variables include eclipsing binary stars and rotating stars such as pulsars,
the cores of supernovae whose electromagnetic radiation is only visible when the beam is
directed at Earth.
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Passage 3
From our corner of the galaxy, these stars are the most brilliant signposts in the heavens
and can be enjoyed even from the light-polluted hearts of major cities.
1- Sirius, All stars shine but none do it like Sirius, the brightest star in the night
sky.
Aptly named, Sirius comes from the Greek word Seirius, meaning, "searing" or "scorching."
Blazing at a magnitude of minus 1.42, it's twice as bright as any star in our sky besides
the Sun.
Sirius resides in the constellation Canis Major, the Big Dog, and is commonly called
the Dog Star.
In ancient Greece the dawn rising of Sirius marked the hottest part of summer—the season's
"dog days."
Sirius no longer marks the hottest part of summer, because it now rises later in the
year.
This happens because the Earth has been wobbling slowly around its axis in a 25,800-year cycle.
This wobble—called precession—is caused by the gravitational attraction of the Moon
on Earth's equatorial bulge, and it gradually changes the locations of stars on the celestial
sphere.
The best time to see Sirius is probably in winter (for northern-hemisphere observers),
because it rises fairly early in the evening.
In 1844, the German astronomer Friedrich Bessel observed that Sirius had a wobble, as if it
were being tugged by a companion star.
And in 1862, Alvan Clark solved this mystery (while testing his new 18.5-inch lens, the
largest refracting telescope in the world at that time).
Clark discovered that Sirius was not one star but two.
This proved to be the first discovery in what became a whole class of stars: the compact
stellar remnant or white dwarf.
These are stars that, once depleting all their hydrogen, collapse to a very dense core.
Astronomers have calculated that Sirius's companion—dubbed Sirius B—contains the
mass of the Sun in a package as small as the Earth.
Sixteen milliliters of matter from Sirius B (that is, about one cubic inch of the stuff)
would weigh 2000 kilograms on Earth.
At magnitude 8.5, it is one four-hundredth as luminous as the Sun.
The brighter and larger companion is now known as Sirius A.
2- Canopus, Canopus resides in the constellation Carina, the Keel.
Carina is one of three modern-day constellations that once formed the ancient constellation
of Argo Navis, named for the ship Jason and the Argonauts sailed in to search for the
Golden Fleece.
Two other constellations form the sail (Vela) and the stern (Puppis).
In modern odysseys, spacecraft like Voyager 2 used the light from Canopus to orient themselves
in the sea of space.
Canopus is a true powerhouse.
Its brilliance is due more to its great luminosity than its proximity.
This number two on our list of stars has 14,800 times the intrinsic luminosity of the Sun!
But at 316 light-years away, it's more than 37 times as far from us as the number one
star, Sirius.
With a magnitude of minus 0.72, Canopus is easy to find in the night sky, though it is
only visible at latitudes south of 37 degrees north.
3- Alpha Centauri, Alpha Centauri (or Rigel Kentaurus, as it is also known) is actually
a system of three stars gravitationally bound together.
The two main stars are Alpha Centauri A and Alpha Centauri B. The tiniest star in the
system is Alpha Centauri C, a red dwarf.
The Alpha Centauri system is a special one.
At an average distance from us of 4.3 light-years, these stars are our nearest known stellar
neighbors.
Centauri A and B are remarkably Sun-like, with Centauri A a near twin of the Sun (both
are yellow G stars).
In comparison to the Sun, Alpha Centauri A is 1.5 times as luminous and shines at a magnitude
of minus 0.01 while Alpha Centauri B is half as luminous and shines at magnitude of 1.3.
Alpha Centauri C is one seven-thousandth as bright and shines at eleventh magnitude.
Of the three stars, the smallest is the closest to the Sun, 4.22 light-years away.
Because of its proximity, it is known as Proxima Centauri.
When night falls and the skies are clear in summer, the Alpha Centauri system shines at
a magnitude of minus 0.27, low in the southern sky.
You can find it at the foot of the Centaur in the constellation Centaurus.
4- Arcturus, Arcturus is the brightest star in the northern celestial hemisphere.
(The first three stars on this list are actually in the southern celestial sphere, though seasonally
they are visible from the northern hemisphere of Earth).
Known as the Bear Watcher, Arcturus follows Ursa Major, the Great Bear, around the north
celestial pole.
The name itself derives from the Greek word arktos, meaning bear.
Arcturus is an orange giant, twice as massive and 215 times as bright as the Sun.
It takes 37 years for the light of Arcturus to reach us, so when we gaze upon it, we are
seeing the star as it looked 37 years ago.
It glows at a magnitude of minus 0.04 in our night sky.
A variable star, Arcturus is in the last stages of life.
During its internal struggle between gravity and pressure, Arcturus has swelled to 25 times
the Sun's diameter.
5- Vega, The name Vega comes from the Arabic word for "swooping eagle" or "vulture."
Vega is the luminary of Lyra, the Harp, a small but prominent constellation that is
home to the Ring Nebula (M57) and the star Epsilon Lyrae.
The ring is a luminous shell of gas resembling a smoke ring or a doughnut that was ejected
from an old star.
Epsilon Lyrae appears to the naked eye as a double star, but through a small telescope
you can see that each of the two individual stars is itself a double!
Epsilon Lyrae is popularly known as the "double double."
Vega is a hydrogen-burning dwarf star, 54 times as luminous and 1.5 times as massive
as the Sun.
At 25 light-years away, it is relatively close to us, shining with a magnitude of 0.03 in
the night sky.
6- Capella, Capella is the primary star in the constellation Auriga (the Charioteer),
and the brightest star near to the north celestial pole.
Capella is actually a fascinating star system of four stars: two similar class-G yellow-giant
stars and a pair of much fainter red-dwarf stars.
The brighter yellow giant, known as Aa, is 80 times as luminous and nearly three times
as massive as the Sun.
The fainter yellow giant, known as Ab, is 50 times as luminous as the Sun and two-and-a-half
times as massive.
The combined luminosity of the two stars is the equivalent of about 130 Suns.
The Capella system is 42 light-years away, its light reaching us with a magnitude of
0.08.
7- Rigel, On the western heel of Orion, the Hunter, rests brilliant Rigel.
In myth, Rigel marks the spot where Scorpio, the Scorpion, stung Orion after a brief but
fierce battle.
Its Arabic name means the Foot.
Rigel is a multiple-star system.
The brighter component, Rigel A, is a blue supergiant that shines a remarkable 40,000
times stronger than the Sun!
Although it's 775 light-years distant, its light shines bright in our evening skies,
at magnitude 0.12.
8- Procyon, Procyon resides in the small constellation of Canis Minor, the Little Dog.
The constellation symbolizes the smaller of Orion's two hunting dogs (the other is, of
course, Canis Major).
The word procyon is Greek for "before the dog," for in the northern hemisphere, Procyon
announces the rise of Sirius, the Dog Star.
Procyon is a yellow-white, main-sequence star, twice the size and seven times as luminous
as the Sun.
Like Alpha Centauri, it appears so bright because at 11.4 light-years, it is relatively
close.
9- Achernar, Achernar is derived from the Arabic phrase meaning "the end of the river,"
an appropriate name for a star that marks the southernmost flow of the constellation
Eridanus, the River.
Achernar is the hottest star on this list.
Its temperature has been measured to be between 13,000 and 19,000 degrees Celsius.
Its luminosity ranges from 2,900 to 5,400 times that of the Sun.
Shining at magnitude 0.45, its light takes 144 years to reach your eye.
10- Betelgeuse, Don't let Betelgeuse's ranking as the tenth-brightest star in the sky fool
you.
Its distance—430 light-years—hides the true scale of this supergiant.
With a whopping luminosity of 55,000 suns, Betelgeuse still shines bright in our skies
at a magnitude of 0.5.
Thanks For Watching Everyone!!
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