Engage – Story of a Star
Stars!!
When you look at the night sky you can see many beautiful stars, there are several different kinds of stars in the sky. All of the stars might appear to be similar, but they are quite different. Like people, they vary in age and size, but stars also vary in temperature and brightness.
Properties of STAR!!
Stars are giant balls of hot glowing gas. They have different properties like below
Size: Sun has a diameter of 1.392 million km, which is approximately 109 times earth. Few stars have been found that are 500 to 800 times larger than the sun. Some very old stars are smaller than the Earth.
Age: Stars live billions of years. Our sun is 4.6 billion years old.
Distance from the earth: The distance between the stars is measured by a unit called “Light year”, it’s the distance travelled by light in one year which is equal to 9.5 trillion kilometres. The nearest star Rigil Kentaurus is 4.3 Light years from earth. (Check the table below for details)
Brightness: When you look at constellations, you’ll notice that some stars are brighter than others. For example, Sirius looks much brighter than Rigel. Is Sirius a brighter star, or is it just closer to Earth, making it appear to be brighter? As it turns out, Sirius is 100 times closer to Earth than Rigel is. If Sirius and Rigel were the same distance from Earth, Rigel would appear much brighter in the night sky than Sirius would.
When you refer to the brightness of a star, you can refer to its absolute magnitude or its apparent magnitude. The absolute magnitude of a star is a measure of the amount of light it gives off. A measure of the amount of light received on Earth is the apparent magnitude. Lower the magnitude brighter the star is!! (Check the table below for details)
Composition: Astronomers study the composition of stars by observing their spectra.
When fitted into a telescope, a spectroscope acts like a prism. It spreads the light out in the rainbow band called a spectrum. When light from a star passes through a spectroscope, it breaks into its component colors.
Color: The color of a star indicates its temperature. For example, hot stars are a blue-white color. A relatively cool star looks orange or red. Stars that have the same temperature as the Sun have a yellow color. (Find the color of the stars in the chart)
Properties Brightest stars in the sky!!
| Common Name | Distance (light years) |
Apparent Magnitude |
Absolute Magnitude |
Temperature (kelvin) |
Constellation |
| Sun | 93 million miles | -26.72 | 4.8 | 5800 | – |
| Sirius | 8.6 | -1.46 | 1.4 | 9600 | Canis Major |
| Canopus | 74 | -0.72 | -2.5 | 7600 | Carina |
| Rigil Kentaurus (Alpha centauri A, B and proxima century) | 4.3 | -0.27 | 4.4 | 5800 | Centaurus |
| Arcturus | 34 | -0.04 | 0.2 | 4700 | Boötes |
| Vega | 25 | 0.03 | 0.6 | 9900 | Lyra |
| Capella | 41 | 0.08 | 0.4 | 5700 | Auriga |
| Rigel | ~1400 | 0.12 | -8.1 | 11,000 | Orion |
| Procyon | 11.4 | 0.38 | 2.6 | 6600 | Canis Minor |
| Achernar | 69 | 0.46 | -1.3 | 22,000 | Eridanus |
| Betelgeuse | ~1400 | 0.45 | -7.2 | 3300 | Orion |
| Hadar | 320 | 0.61 | -4.4 | 25,000 | Centaurus |
| Acrux | 510 | 0.76 | -4.6 | 26,000 | Crux |
| Altair | 16 | 0.77 | 2.3 | 8,100 | Aquila |
| Aldebaran | 60 | 0.85 | -0.3 | 4,100 | Taurus |
| Antares | ~520 | 0.96 | -5.2 | 3,300 | Scorpius |
| Spica | 220 | 0.98 | -3.2 | 2,600 | Virgo |
| Pollux | 40 | 1.14 | 0.7 | 4,900 | Gemini |
Fusion: What makes Stars shine!!
For centuries, people were puzzled by the questions of what stars were made of and how they produced light. Many people had estimated that Earth was only a few thousand years old. The Sun could have been made of coal and shined for that long. However, when people realized that Earth was much older, they wondered what material possibly could burn for so many years.
In the 1930s, scientists discovered reactions between the nuclei of atoms. They hypothesized that temperatures in the center of the Sun must be high enough to cause hydrogen to fuse to make helium. This reaction releases tremendous amounts of energy. Much of this energy is emitted as different wavelengths of light, including visible, infrared, and ultraviolet light. Only a tiny fraction of this light comes to Earth. During the fusion reaction, hydrogen nuclei combine to create one helium nucleus. The mass of one helium nucleus is less than the mass of four hydrogen nuclei, so some mass is lost in the reaction.
Years earlier, in 1905, Albert Einstein had proposed a theory stating that mass can be converted into energy. This was stated as the famous equation E =mc^2 produced, m is the mass, and c is the speed of light. The small amount of mass “lost” when hydrogen atoms fuse to form a helium atom is converted to a large amount of energy. In this equation, E is the energy
Evolution of the star!!
Nebula Stars begin as a large cloud of gas and dust called a nebula. As the particles of gas and dust exert a gravitational force on each other, the nebula begins to contract. Gravitational forces cause instability within the nebula. The nebula can break apart into smaller and smaller pieces. Each piece eventually might collapse to form a star. See what happens next in the picture below
