Characteristics of a Star: Color, Temperature, Age of Stars

A star is defined as an astronomical object which consists of a luminous spheroid made of plasma, which is held inside it due to its own gravity. Since sun is the nearest star to the earth which is 39.9 trillion Km or 4.2 light-years away from us but even many other stars are also visible to us at night which appear as a crowd having fixed luminous points in sky due to their huge distance from earth. Stars are not uniformly distributed in universe, but actually they are grouped into galaxies along with interstellar gas and dust. According to the research, our universe contains 1024 stars and most of them are not visible to us because they lie out of galaxy; Milky Way. Stars present in the Milky Way galaxy are made of 71% hydrogen and 27% helium. Here Characteristics of a Star are being discussed in detail.

Why do stars shine in the night?

Well the beauty of a star i.e. its shine, is due to the thermo-nuclear fusion reaction from hydrogen to helium, occurring in the core of a star which creates an immense amount of energy in form of gamma rays. These gamma rays are converted into visible light until reaching on the surface of star, as they lose energy during travelling and they require 100,000 years to reach on surface of star. Then this visible light is emitted in outer space. Mass, age, chemical composition and many other properties can be investigated by astronomers by observing their motion in space, luminosity and spectrum, respectively. The thing which keeps a star bound is the 2 forces. The force of gravity of a star pulls it towards center while fusion reaction tries to expand it. In the case, if fusion released energy wins, then a star dies.

When much amount of hydrogen is converted in to helium then a star moves towards its end. Helium blows up the core of star and as the result temperature of star rises which causes an expansion in its outer shell of hot gases. Such large stars are known as red giants. But the main factor that decides the end of a star is its mass; more mass, less life.

Why do stars twinkle?

Since sun is the nearest star to our earth so it seems to be like a disc and provides day light. While the other stars, which are far distant seems to be like shinning points in night sky. After sun, the second big star is R Doradus. Angular diameter of star R Doradus is 0.057 arc seconds. The stars in sky twinkle because of the effect of earth’s atmosphere. As light from a star travels through our atmosphere, it bounces and bumps its way through the various layers, bending the light until it reaches you. Since the hot and cold layers of air are constantly changing, the bending of light shifts as well, thus causing the star to twinkle.

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What is a neutron star?

A neutron star is defined as a celestial body with a relatively small radius (typically 30 km) and a very high mass, primarily consisting of tightly packed neutrons. Neutron stars are believed to be formed from a supernova explosion from the gravitational collapse of a giant star’s remnant, because the star is not giant enough to create a black hole.

Characteristics of a Star

Birth of a star

What is Star? Birth, Magnetic Field, Diameter, Temperature and Luminosity

A star is born when atoms of light elements are squeezed to under sufficient pressure to fuse their nuclei. All stars are the result of a balance of forces: gravity compresses atoms in interstellar gas until the reactions to the fusion start. And they exert an outward pressure once the fusion reactions begin. The star remains stable, as long as the inward force of gravity and the outward force generated by the fusion reactions are equal.

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Age of a star   

Most of the stars in universe are 1-10 billion years old. Age of star depends upon its mass. The more massive a star, the shorter its lifetime will be. The reason is that if a star is massive then definitely, it has greater pressure in its core which causes rapid burning of hydrogen. Until now, most massive star has lasted an average life of few million years. A star having minimum mass can last up to billions of years.

Magnetic field of a star

What is Star? Birth, Magnetic Field, Diameter, Temperature and Luminosity

A stellar magnetic field is a magnetic field generated within a star by the movements of conductive plasma. This motion is created through convection, which involves the physical movement of material as a form of energy transport.

Color of stars

In electromagnetic spectrum, blue color dominates the visible light which is actually the output of hot stars. However, red color is possessed by the cool stars. Color of a star doesn’t depend upon its distance from you however distance can impact its brightness.

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Temperature of star is one of the most important characteristics of a star. The maximum temperature of a star, up to present research, is 40,000 K and minimum temperature is 2000 K. Our sun has a greenish yellow color as its temperature is 6000 K, but in space sun seems to be white, mean it is shining with same amount of red and blue wavelengths at that time. When we see sun from earth, then its color is yellowish due to the scattering of the nitrogen molecules with beams of sunlight (reaching us) and hence light of longer wavelength is left behind. Similarly, sky is blue due to scattering of sunlight with atmosphere of earth. Here are some stars with their colors and approximate temperatures.

  • Spica 25,000K               blue color
  • Vega 10,000K                white
  • Sun 6,000 K                   yellow
  • Aldebaran 4,000K          orange
  • Betelgeuse 3,000K          red

What is Star? Birth, Magnetic Field, Diameter, Temperature and Luminosity

White and blue color is for immense hot stars while red color indicates cooler stars.

Luminosity of a star

Some stars on sky shine more brightly than others do, this is because of the energy which they put with them. Characteristics of a Star also include luminosity. Luminosity is the amount of light and other forms of radiant energy which are emitted by a star per unit time. It has same unit as power has. Luminosity can be determined by radius and surface temperature of a star. There are some stars which don’t radiate uniformly across entire surface. The most rapidly rotating star is Vega and its energy flux at poles is greater than along its equator.

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