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--------------------------------- 2416 - STARS - come in all shades and sizes
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- Astronomers have measured the accurate distances of 20,000 stars and still counting. Yet, it is estimated that in the Observable Universe there are over:
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--------------- 100,000,000,000,000,000,000,000 stars. (10^23).
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- Of course, the maximum distance we can “accurately” measure today is 300 lightyears. The Observable Universe in both directions has a diameter of 28,000,000,000 light years. So, we have a ways to go in distance measurements. And, the edge of the Universe is disappearing from our sight. The light will never reach us.
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- Stars come in all shades and sizes. However, the largest stars are all over 400 lightyears away, too far for today’s accurate distance measurements. These most massive stars are Blue in color.
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- The closet Blue star is Zeta Ophiuchi, which is between 417 and 509 lightyears away. Outside our accurate measurement reach. It is a Blue Supergiant that will go supernova in a few million years and end up a Black Hole.
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- You can tell the temperature of a star by its color. Zeta Ophiuchi is Blue and its surface temperature is 35,000 degrees Kelvin. Color is another word for frequency of radiation. And, frequency is another word for the wavelength of the radiation.
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------------------------ Wavelength = constant velocity of light / frequency
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- You measure the brightness, or energy of radiation, at different wavelengths. When you locate the wavelength of the maximum brightness, or maximum intensity of radiation, at that wavelength the temperature is equal to Peak Wavelength / .0029.
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- This is known as Wien’s law. Our Sun looks yellow to our eyes but measuring its maximum radiation energy occurs at 500 nanometers wavelength, which is blue-green in color. Using Wien’s law the surface temperature of the Sun is 5,800 Kelvin.
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-------------------- Below is a table of the color of a star and the maximum temperature:
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-------------------- Blue 49,000 Kelvin
-------------------- Blue-White 31,000
-------------------- White 10,000
-------------------- White-Yellow 7,400
-------------------- Yellow 6,000
-------------------- Orange 5,300
-------------------- Red 3,900
-------------------- Red-Infrared 2,200
-------------------- Infrared 1,200
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- The largest Blue stars are known as Wolf-Rayet stars. They are the class of stars that have burned all their fuel and are just about to go supernova. They are so big and have so much gravity that after burning their hydrogen fusing into helium, helium fuses into carbon, carbon fuses into neon, neon fuses into oxygen, oxygen fuses into silicon, and silicon fuses into iron.
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- All of these fusion layers are like layers on an onion in a Wolf-Rayet star with iron at the center. There is no fusion higher than iron because iron fusion absorbs energy rather than emitting energy. Without emitting radiation the star collapses due to gravity.
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- The collapse at the core bounces sending the higher level elements out into a supernova explosion. The closest Wolf-Rayet star is Gamma Velorum which is 740 to 975 lightyears away. In the Constellation Vela, it is just outside our measurement range.
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- The problem here is that until we know the distance accurately we can not accurately determine the properties of a star. We want to learn more of the properties of the massive stars because they were the first stars formed after the Big Bang, about 180,000,000 years after the Big Bang.
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- Often massive stars appear as binary stars. Two stars that are orbiting each other. Understanding how these massive stars form will help us understand how stars formed in the early Universe.
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- The closet star is 4 lightyears away. It is Alpha Centauri and it is actually a three star system. To illustrate the distance of being 4 lightyears away, if you reduced the Sun to the size of a marble, Alpha Centauri would be 2 marbles and a ball bearing 250 miles away. (See Review #388)
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- The closest Blue-White star, Regulus in the Constellation Leo, is 78 lightyears away. It is 331 times brighter than our Sun at 28,000 Kelvin. Spica and Rigel are also Blue-White stars. Spica in the Constellation Virgo is 262 lightyears away, 25,000 brighter than the Sun. Rigel in the Constellation Orion is 773 lightyears away, 180 times brighter.
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- Less than 1% of the stars within 100 lightyears rank as massive stars, greater than 10 solar mass. The biggest star we know is the Pistol Star. The Pistol is 150 to 200 solar mass and more than 25,000 lightyears away. It has more radiation in 6 seconds than our Sun has in one year.
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- The most distant supernova is pegged at 11,300,000,000 lightyears away. It was 2,000,000,000 times brighter than our Sun in 1997. Today it is no longer visible.
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- The closest supernova occurred in 1987, just 170,000 lightyears away. It was 250 times brighter than our Sun. The farthest supernova we could see with the naked eye in 1885 was M31 in Andromeda Galaxy 2,500,000 lightyears away.
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- The farthest star we can see with the naked eye is S - Carinae. It is 12,000 lightyears away. It is a variable star and currently at its brightest 5.6 Magnitude.
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- ( See #622 - Polaris for an explanation of a star’s brightness Magnitude.)
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- The hottest star has a temperature of 211,000 Kelvin and is 1,100 times brighter than our Sun. It is 7,100 lightyears away. The hottest star we can see with the naked eye is Zeta Puppis, a Blue Supergiant in the Constellation Puppis. It is 1,400 lightyears away with a surface temperature of 42,000 Kelvin. 7 times hotter than our Sun, 20 times larger, 60 times more massive, and 800,000 times brighter. Zeta Puppis is only 6,000,000 years old.
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- The coldest star is a White Dwarf just 145 lightyears away. It is 4,300 Kelvin and has a luminosity of .00002 that of our Sun; it is the coldest because it has a very small surface area with a radius 1/100 that of our Sun.
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- The coldest and the largest star we can see with the naked eye is Cassiopeiae. It is 350 lightyears away, orange red with a surface temperature of 2,000 K, 1/3 that of our Sun, but it is 1,800 times larger than our Sun. A variable star at 4.8 Magnitude at its brightest.
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- The second closest star is Barnard’s star. It is a Red Dwarf just 6 lightyears away and traveling at 87 miles per second (313,200 miles per hour). (See Review #362)
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- It is not the fastest star, Kapteyn’s Star is also a Red Dwarf at 12.8 lightyears away traveling at 175 miles per second ( 630,000 miles per hour). (See Review #616)
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- Here is a table of the sizes of stars relative to our Sun and their color:
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-------------------- Blue 25 solar mass Luminous Supergiant
-------------------- Blue-White 15 Supergiant
-------------------- White 3 Bright Giant
-------------------- White-Yellow 1.5 Giant
-------------------- Yellow 1 Sun size
-------------------- Orange .75 Dwarf
-------------------- Red .5 Red Dwarf
-------------------- Red-Infrared - White Dwarf
-------------------- Infrared - Brown Dwarf
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- (See #617 and See #626 for more reviews about Brown Dwarfs)
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- Our Milky Way Galaxy is in constant rotation and some stars will be closer to us in the future. In 1,360,000 years from now the star Gliese 710 which is now 63 light years away will come within 1 light year away.
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- The gravity it brings will seriously dislodge comets from the Oort Cloud and rain comets on Earth much like occurred during Earth’s early formation. You can see the evidence of that rain with a close look at the Moon.
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- In just 27,000 years Alpha Centauri will be within 3 lightyears away. The Oort Cloud of comets extends out about 2 lightyears from us, but Alpha Centauri could still have some dislodging affects.
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- If a supergiant gets that close it would shine with the light of 20 full moons. Not only do stars come in all shades and sizes they are all changing as well.
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- Wish upon a star, you have many choices.
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- Other Reviews available upon request:
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- 2272 - Names of stars.
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- 2273 - The diversity of stars.
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- 2238 - The age of stars.
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- 2038 - Hyper - velocity stars.
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- 1822 - The the largest stars and the oldest stars. This review lists 12 more reviews about stars.
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- July 11, 2019 623
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--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
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--------------------- Friday, July 12, 2019--------------------
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