My Science School

 

 

What are Cataclysmic Variables?

Two types of variable stars, called Novae and Supernovae, are classified as Cataclysmic Variables since their increase in brightness is accompanied by a spectacular flare up or explosion.

 

 

 

What are Quasars?

A quasar is the abbreviation for Quasi-stellar object (QSO). Quasars are star-like in appearance but have certain special characteristics that differentiate them from ordinary stars.

When was the first Quasar discovered?

The first Quasar was discovered in 1963 by the Mount Wilson and Palomar Observatories in USA.

How far away are Quasars?

Quasars exist at Cosmological distances, typically over fifteen billion light years away.

What are the special characteristics of Quasars?

Quasars seem to be moving at speeds faster than of any known galaxy, and at more than 90% of the speed of light. The energy emitted by a Quasar is about a hundred times more than the energy emitted by an entire galaxy. However, the diameter of Quasar is unbelievably compact. Quasars emit light which is extremely blue in colour and varying rapidly in brightness.

What is the explanation for the special characteristics of quasars?

As yet no one has given a satisfactory explanation and Quasars remain among the most enigmatic objects in the universe. They are thought to be at the centre of galaxies, their brilliance emanating from the stars and gas falling towards and immense black hole at their nucleus.

Which star other than Sun is the nearest to the Earth?

The star Proxima Centauri in the Constellation Centaurus which is at a distance of nearly 40 trillion km from Earth. It is a faint red Dwarf visible only with a telescope.

 

 

 

 

 

What are Variables?

Variables or ariables stars are stars whose brightness increases and decreases periodically.

 

 

 

What are Cepheid Variables?

An Cepheid Variable is a type of variable star. Cepheid variables vary in magnitude over a period from one to sixty days. Also, the longer the period the more luminous the star.

Why are Cepheid Variables important to astronomers?

Since the period and luminosity of a Cepheid Variable are closely related, one can obtain the absolute magnitude of the star by observing its period. Cepheid variables are therefore used by astronomers as “Standard candles” for comparing with other stars.

What is a white dwarf?

A red giant starts shrinking when its stock of hydrogen is nearing exhaustion. At a certain stage, the star becomes so dense that ever its gravity cannot matter in which shrink it any more. White dwarfs consist of degenerate matter in which gravity has packed the protons and electrons together as tightly as is physically possible so that a spoonful of it, weighs several tonnes. At this stage, the star becomes stable again though it is much smaller in size than it was at the red giant stage. The star is now called a white dwarf.

How does a white dwarf shine?

A white dwarf shines mainly by radiating away its stored internal energy, besides the fusion of any residual helium into other heavier elements. It slowly cools and darkness over millions of years.

 

 

 

What is a black dwarf?

A white dwarf shines by radiating its internal energy. When the internal energy is completely exhausted the star ceases to shine and becomes a cold, dark body called a black dwarf. 

What happens when the hydrogen in the star is completely converted to helium?

As the hydrogen gets depleted the outward force of the fusion reaction starts diminishing and the inward force caused by the star’s gravity gains the upper hand. Consequently, the star begins to shrink in size as well as increase in brightness. Its colour also changes from red to white.

How much energy is produced by the helium fusion reaction?

Almost 95% of the total energy that a star can generate through fusion reactions is generated through hydrogen fusion. The fusion of helium and heavier elements will account for just over 5% of the total energy that a star can generate.

 

How long is the fusion reaction in a star likely to go on?

Once the hydrogen and the helium fusions stop due to the exhaustion of their supply, the fusion reactions may continue to produce heavier elements but energy generated by these reactions is rather negligible. The fusion reaction will continue until all the matter in the star is completely converted to the element iron. The star will then radiate energy only by depleting its stock of accumulated internal energy.

Does the fusion reaction in a star always priced to the iron stage?

Generally, the fusion reaction in all stars will proceed to the helium fusion stage. However, the extent to which it proceeds beyond this stage depends on the amount of pressure and temperatures developed at the core of the star. The larger the star the larger will be the number of fusion stages it will go through before the fusion reaction stops.

How massive must a star be to completely convert into iron?

Foe a star to completely convert into iron, it must be at least 30 times as massive as the Sun.

Why does the fusion reaction stop when all the matter is converted into iron?

The pressure created in the cores of ordinary stars is insufficient to continue the fusion reaction beyond the element iron.

 

 

What is a red giant?

In the transition of the star to the red giant stage, its inner part or core shrinks, while its outer part or envelope expands. A red giant is a star with a relatively low effective temperature and a large radius. The low temperature makes the star glow red and the larger size makes it a giant compared to its original size.

What are the other characteristics of red giants?

Red giants are highly luminous and may have luminosities ranging from about 100 to even 10,000 times that of the Sun. They are very bright because they are so large although their surface temperature is lower than that of the Sun. The density of red giants is also extremely low ranging from 10-4 to 10-7 times the Sun’s mean density. In other words, the mean density of a typical red giant is less than that of air at sea level.

Will the Sun become a red giant?

The Sun will a red giant almost the size of Betelgeuse in about five to six billion years.

Why does a star become a red giant?

As the hydrogen fusion in the star progresses, its mass moves towards the centre of the helium increases at the star’s core, the pressure also increases.

At a certain stage, the pressure is sufficient to start the helium fusion reaction when helium fuses to from carbon and other heavier elements. Now, the outward force of the combined hydrogen and helium fusion reactions as well as the outward pressure is greater than the inward force. The star therefore starts expanding into a red giant and regains equilibrium at a larger size.

 

 

What are super giants?

Super giants are red giants having extremely large size and luminosity compared to a typical red giant. A typical red super giant would be about 100times as luminous as a typical red giant.

How big is a super giant?

If the super giant Betelgeuse occupied the position of the Sun, all the planets up to and including Mars would be contained within it. Thirty million replicas of Sun could fit inside the super giant Antares.

 

 

 

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.

 

How long does the Sun take to complete one revolution around the centre of the Milky Way galaxy?

About 225 million years. This is also called the cosmic year or cosmological year.

What was the stage of evolution of the Earth one cosmic year ago?

One cosmic year ago ‘Coal Forests’ still existed on the Earth, which was later transformed into coal deposits. Human beings had not yet appeared on the Earth.

 

 

 

 

How large is the Sun compared to the earth?

The Sun’s mass is 333,000 times that of the Earth. However, average density of solar matter is only one fourth that of Earth. Hence more than a million Earths would fit inside the Sun. Also, 1098 Earths would have to be placed side by side to equal the diameter of the Sun which is 1,392,000 km.

 

 

 

 

 

 

What is the period of spinning of the Sun about its axis?

Since the Earth’s surface is solid, all parts on its surface rotate in unison. However, since the Sun is appreciably gaseous, it rotates faster in its equatorial region than in its polar regions.

Is the Sun’s axis titled to the plane of the Earth’s orbit?

Yes, by about 70.

Does the Sun have a magnetic field?

Yes.

What is the temperature of the Sun?

The temperature of the Sun is about 60000C near the surface and about 14 million degrees Celsius at the core.

What is the distance between the Earth and the Sun?

The distance between the Earth and Sun varies from a maximum of 152*106  km at aphelion to a minimum of 147*106 km at perihelion. The average or mean distance is therefore about 149.6*106 km.

If we could ‘fly’, in our imagination, how long would it take to reach the Sun?

At the speed of the Concorde, the fastest passenger plane, it would take less than three hours to fly from New York to London, but to fly a distance equal to that between the earth and the Sun, it would take nearly eight years.

What percentage of the total mass of the Solar System is contributed by the Mass of the Sun?

Over ninety-nine per cent.

Can the Sun ever be seen steadily with the naked eye?

Seeing the Sun steadily with the naked eye will cause permanent damage to the eye except during a total solar eclipse. It can, however, be viewed through special filters which make the Sun appear darker.

At what speed is the Sun moving as it orbits the Milky Way galaxy?

About 275 km/sec.

How long it take the light from the Sun to reach the Earth?

Just under eight and half minutes.

 

What is albedo?

Albedo refers to the proportion of incident light reflected back in all directions from the surface of a body. A perfect reflector has an albedo of 1, and a perfect non-reflector has an albedo of 0. The term usually applied to celestial objects within the solar system. A planet with clouds and atmosphere will have a higher albedo. The Moon has an albedo of 0.07 as it absorbs 93% of the sunlight falling on it and reflects the Balance 7%. The albedo of atmosphere less Mercury is 0.06, while Earth and Venus have albedos of 0.39 and 0.76 respectively.

 

 

What is the effect of albedo on the reflecting body?

The body heats up on absorbing the incident radiation. Hence a planet with a low albedo would warm up more, when sunlight falls on it.

What are the objects near zero albedos?

Some of the asteroids have up more, when sunlight falls on it.

 

What is the empty focus?

An ellipse has not focus but two foci, one at each end. Kepler’s laws specify the Sun focus of the planet’s elliptical orbit.

The other focus of the elliptical orbit is referred to as the empty focus. The distance between the empty focus and the aphelion point is equal to the distance between the sun and the perihelion point.

 

 

 

 

Which planet has a red spot?

Jupiter has a large red spot which keeps shifting and changing. The spot is believed to be an area of permanent turbulence.