Category Science

What is the main sequence?

The main sequence refers to the long period when the star shines steadily and brightly. Our Sun is now at the main sequence stage.

What is stellar evolution?

Stellar evolution refers to the stages in the evolution of a star as follows:

1. The star begins as a cloud of interstellar material perhaps a light year in radius.
2. The cloud contracts and also heats up for a few million years.
3. A spherical star shape, called a proto-star, begins to emerge. The temperature is about 20000C.
4. The proto-star begins heating up and the fusion reaction begins. The star flares up in a short interval of time and stars glowing. At this stage, the luminosity of the star may increase to several hundred times the Sun’s present luminosity.
5. The star cools down to a steady equilibrium stage. The main sequence stage is reached and continuous for some ten billion years.
6. The star starts growing and the luminosity starts decreasing.
7. The star becomes a red giant and continuous in that state for a few hundred million years.
8.  The red giant starts shrinking. The luminosity increases.
9. The star becomes a white dwarf and continuous to shine for a few billion years at the expense of its internal energy.
10. The star exhausts all its internal energy and ceases to glow. The star has now become a black dwarf and reached the final stage of stellar evolution.

What happens to the radius of the star as it passes through the ten stages of evolution?

The radius of the star continuously decreases through the various stages except at the red giant stage when it temporarily increases.

How does a star form?

Over a period, particles of matter from space debris coalesce through gravitational forces to form a heavenly body which is rotating and has a spherical. As the matter continues to coalesce, the body becomes denser and the pressure at its centre increases. If the mass of the body is sufficiently large, the high pressure at the centre causes the hydrogen fusion reaction to commence. The mass is then called a proto-star. If the body is still larger the hydrogen fusion activity increases and makes the body glow brightly. The body is then called a star.

What happens when a star starts glowing?

After a star start glowing, it reaches an equilibrium state when the outward explosive force of the hydrogen fusion reaction equals the inward force caused by the star’s gravity. The star will when continue glowing at virtually a steady rate remain at a steady size for a very long period.

What is the shape of the Milky Way galaxy?

The Milky Way galaxy consists of a central core or nucleus with many stars, a disc with many stars distributed in a plane titled at 620 to the celestial equator, and a halo with relatively few stars distributed in an outer region. The Sun is situated about three fifths of the way from the centre of the galaxy.

How can proto-stars be detected?

As the interstellar cloud contracts to form a proto-star, it heats up and radiates infra-red rays which can be detected by instruments.

At what stage of the proto-star does the hydrogen fusion reaction start?

The hydrogen fusion reaction starts when the temperature at the core of the star reaches about ten million degrees Celsius.

What is the solar wind?

The solar wind is solar radiation in the form of a steady stream of electrically charged particles mostly protons and electrons which pours out of the Sun at the speed of upto 150,000 km/sec. The particles are however smaller than atoms.

What happens when the solar wind hits the Earth?

The solar wind is deflected by the Earth’s magnetic field and does not touch the Earth. The deflected solar wind streams behind the Earth similar to a cometary tail.

Does the Solar wind have any effect on the Earth?

Since the particles of the solar wind are electrically charged, they tend to move towards the Earth’s magnetic poles, making the sky in the Polar Regions glow in vivid patterns called aurorae.

What is the solar limb?

The solar limb is the edge of the Sun’s disc.

What is the solar atmosphere?

The portion of the Sun lying in the region outside the limb is called the solar atmosphere.

Is the solar atmosphere normally visible from the Earth?

No. The intense brightness of the Sun’s disc prevents us from seeing anything else in the vicinity. The solar atmosphere can however be seen during a total solar eclipse when the Sun’s disc is totally covered by the Moon.

What is the nature of radiation from the Sun?

Radiation from the Sun travels in waves of energy. There are different types of waves depending on wavelength, such as light, X-rays, gamma rays, radio waves etc.

Can all types of radiation from the Sun be detected on the Earth?

We can see light rays and feel heat rays. Ultra violet rays tan our skin.

Radio waves can be detected by instruments. But almost all the other rays from the Sun are absorbed by the earth’s atmosphere before they reach the Earth’s surface and are detectable only by instruments placed on artificial satellites outside the Earth’s atmosphere.

How much matter is converted to energy to produce the Sun’s radiation?

About four million tons of hydrogen is consumed per second to produce the Sun’s radiation which proliferates steadily in every direction.

What proportion of the Sun’s radiation reaches the Earth?

About one billionth of the Sun’s radiation reaches the Earth and the rest streams off into space in all directions.

What is the significance of the absorption of the Sun’s rays by the Earth’s atmosphere?

Some of the Sun’s radiation is harmful to life on the Earth. Hence the Earth’s atmosphere acts as a protective shield by absorbing harmful radiation of the Sun.

What happens in a hydrogen bomb explosion?

In a hydrogen bomb explosion, hydrogen atoms are subjected to collision under tremendous pressure, resulting in their being merged or fused to from element helium. In the process, also called fusion reaction, large quantities of energy area released in the form of heat, light, X-rays, microwaves, gamma rays etc.

At what rate is the hydrogen being consumed in the nuclear reactions taking place in the Sun?

About six hundred million tons of hydrogen is consumed per second.

Has the hydrogen fusion reaction started in Jupiter, the largest planet in the Solar System?

Some astronomers believe that the hydrogen fusion reaction occurs within Jupiter’s core because Jupiter radiates more heat than can be accounted for by conventional explanations. However, Jupiter does not have enough mass to glow and needs to be over a hundred times larger than it is now become a star.

How is the tremendous pressure created in the Sun for sustaining the fusion reaction continuously?

 Hydrogen will convert to helium only under tremendous pressure. Such pressures can be sustained in laboratories on the earth only for a brief instant during which a hydrogen bomb explosion takes place for as fraction of a second.

However, the Sun sustains this pressure continuously and so the explosion is continuous. Due to the enormous gravity of the Sun, the pressure inside the Sun is about 100 billion times the pressure of the earth’s atmosphere and is sufficient to sustain a continuous fusion reaction.

Why the diameter of the Sun relativity is steady and why is its mass not scattered as in a normal explosion?

The large mass of the Sun creates tremendous gravity which forces all the mass towards the centre of the Sun. The centre of the Sun is subject to tremendous heat and pressure, enough to sustain a continuous hydrogen bomb explosion. The explosion acts as an outward force throwing the mass away from the centre of the Sun while the gravity of the Sun acts as an inward force pushing back the mass towards the centre of the Sun. If the two forces are in equilibrium, the Sun would neither expand nor contract. This is what is actually happening. Hence, the Sun’s size does not change appreciably.

What is the Sun made up of?

Hydrogen, the most abundant element in the Universe, is also the main constituent of the Sun, with most of its mass concentrated towards its centre.

Is the Sun a ball of fire?

In an ordinary fire, oxygen combines with various fuels, releasing heat and light. However, the fire in the Sun is not an ordinary fire but is similar to a continuous hydrogen bomb explosion, wherein a small quantity of matter is converted into an enormous quantity of energy in a conversion process that is ten million times more effective than ordinary combustion.