My Science School

Occasionally we see ‘wanderers’ in our Solar System. A comet is a ball made of rock and ice. This nucleus is surrounded by a cloud of gas called the ‘coma’. When comets move close enough to the Sun. they reflect the Sun’s light and form a tail of gas and dust.

Comets leave bits of dust from their tails behind in space. Some of this dust enters the Earth’s atmosphere where it burns up. We may then see a shower of bright ‘shooting stars’. The scientific name for a shooting star is a ‘meteor’.

Sometimes lumps of rock or metal from space crash to the Earth. These are ‘meteorites’. A large meteorite may make a crater where it lands. Meteorites probably caused the craters on the surface of the Moon, Mercury and Mars – as well as this one in Arizona.

 

 

 

This meteor crater in Arizona is over 1 kilometre wide and 175 metres deep.

 

 

 

 

 

 

 

Halley’s Comet

Halley’s Comet is a regular visitor to our part of the Solar System. It returns about every 76 years and has been seen throughout the ages. The diagram shows the strange shape of the comet’s orbit – a long oval. The comet is invisible beyond Saturn’s orbit. You can see how the comet’s tail always points away from the Sun.

The planets and stars are far too far away to see clearly, however good your eyesight is. The telescope was invented to help people look at faint, distant objects and see them in more detail. Telescopes collect more light than the human eye. They can also make things look bigger. Stars looked at through a telescope seem to be brighter and closer.

Telescopes use either a lens or a mirror to collect light and focus it. Another lens is used to produce a magnified image. Modern telescopes are housed in giant buildings called ‘observatories’. These are often built at the top of a mountain where there is a clear view of the sky.

 

 

 

 

 

The telescope

This telescope uses one convex lens to collect and focus light, and another to magnify the image. Sliding the outer tube changes the distance between the two lenses. This is important as it allows you to see objects that are near and far away.

 

 

 

 

 

Looking down on a telescope in the observatory at Kitt Peak, Arizona, USA

Watching the Solar System from the Earth is one way of finding out about it. To learn more, people have used rockets to travel into space. There they have been able to look at parts of the Solar System more clearly. But although the first men landed on the Moon in 1969, no one has visited any of the planets. They are too far away and conditions are dangerous for humans.

However, as you have seen space probes – robot controlled unmanned spacecraft – have been sent far into the Solar System. The space probe Voyager 2 has travelled through the Solar System and is now well beyond the orbit of Pluto. As it travels it takes pictures and sends them back to Earth.

 

 

 

Voyager 2

This space probe gas already travelled across millions of kilometres of space, and has collected information on Jupiter, Saturn, Uranus and Neptune. The craft’s onboard computers are reprogrammed during its flight by electronic signals from Earth. The entire vehicle weighs only 815 kilograms. It carries equipment for 11 scientific experiments which are powered by a nuclear generator.

 

 

 

 

 

This is a photograph of the surface of Mars. The surface of Mars – you can see the solar panels of the lander at the bottom of the photo.

 

Life and death of a star

When a star like our Sun first forms it is different from the way we see it today. At first the Sun was a very hot, blue star. As it grew bigger it cooled down and looked white. The Sun will shine as it is for about 10,000 million years. Eventually it will swell and form a ‘Red Giant’. Some of the stars we see are Red Giants. They are cooler than the Sun. But as they are many times bigger, they appear brighter. A Red Giant slowly cools and shrinks. Its outer layers of gas drift away and a small hot star called a ‘White Dwarf’ is left. This slowly cools and becomes a ‘Black Dwarf’.

 

 

 

 

 

Very large stars

Stars much bigger than our Sun also become Red Giants, but they blow up in a huge explosion called a ‘supernova’. They shrink into themselves and form a ‘Black Hole’. Anything nearby gets sucked into a black hole. Even its own light cannot escape!

                We know that the sun is much bigger than the earth but appears very small because it is very far from our planet. The sun is about 150 million kilometres from the earth. When the sun is overhead its distance is 6000 kilometres less than the rising and the setting sun, which is equal to the diameter of the earth. The distance of 6000 kilometres is negligible as compared to 150 million kilometres and would not make any difference in the size of the solar disc. In case of any difference, the sun at noon would have been looked a bit bigger than that of the size of rising and setting sun. Do you know why do we observe exactly the opposite effect? 

 

 

               The bigger solar disc seen in the morning or in the evening is an optical illusion. If you take a photograph of the morning, noon and evening sun, then you will see that the solar image is of the same size. The optical illusion works for the lunar disc also, and because of this, the rising moon appears quite big.

               The reason for this optical illusion is probably because we tend to compare the size of the rising or the setting sun with earthly objects. When we see a tree, or a building or a ship near the solar disc then the size of the sun appears to be big. At noon, when the sun is overhead, we are not able to compare it with any close by object near the sun. In short, we can say that the bigger appearance of the rising and the setting sun is nothing but just an illusion. In fact, the sun’s size always remains the same.

               We know that there are nine planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. In terms of distance from the Sun, Mars is the fourth planet. It is the outermost of the terrestrial planets and is often called the Red Planet. Do you know why?

               We know that Mercury is the planet closest to the Sun. It rises and sets almost with the Sun. Therefore, we can see it either before sunrise or after sunset. Similarly, we see Venus either sometime before sunrise or sometime after sunset (dusk). But Mars can be seen clearly only for a month or two every other year. Among all the planets Mars is next only to Venus in brightness. Also it is very striking not because of its brightness but for its reddish-yellow colour. To study Mars, man has sent many space probes. These spaceships have provided us with many valuable facts about it. In 1976, the American space probes Viking I and II landed on the Martian surface. They gave valuable information about the atmosphere of Mars. It has been found that the atmosphere of Mars contains 1 to 2 percent argon, 2 to 3 percent nitrogen, 95 percent carbon-dioxide and 0.3 percent oxygen.

               The surface of Mars appears to be made up of bright and dark areas. About 70 percent of the Martian surface is found reddish and yellowish which gives the planet its characteristic colour. These areas constantly change shape. It has many rocks containing rusty iron and is covered with reddish-brown deserts. The winds blow at very high speeds of about 400 km/hr over Mars and create heavy storms in Martian deserts. The storms raise a lot of red dust in the atmosphere. Since Mars has a weak gravitational pull, these dust particles remain in the atmosphere for weeks together. And so Mars, because of its red dusty surface and the dust particles in the atmosphere, appears reddish orange to us.

What is galactic evolution?

There appears to be some evidence of a possible evolutionary progression among the types of galaxies such as normal galaxy radio galaxies, Seyfert galaxies and even some other bodies such as quasars. However, galactic evolution has not been conclusively proved and is still undergoing investigation.

 

 

 

What happens when two galaxies collide?

In spite of the colossal mass of stars and space debris contained in galaxies the mass is very highly dispersed. Though several colliding galaxies have been studied, there does not seem to be any evidence of catastrophic impact.

However, due to the tidal forces, the total masses of both galaxies are redistributed between them, though the two nuclei are comparatively less affected.

 

 

 

What is the Messier List?

The Messier List or Messier Catalogue represents the first attempt to publish a catalogue of heavenly bodies difficult to identify, and contains particular of 109 such objects including remote nebulae and galaxies. The list was prepared to forewarn astronomers who were constantly mistaking these for comets and stars.

What is the Messier Number?

The Messier Number is the identification code of a heavenly body in the Messier Catalogue. An example is the Andromeda galaxy designated as M31.

What are radio galaxies?

They are galaxies emitting a significantly large amount of radiation at radio wave frequencies though not necessarily emitting a large amount of visible light. A strong radio galaxy may be emitting radio power of up to a hundred times that of an ordinary galaxy like the Milky Way.

 

 

 

 

 

 

 

 

 

 

Continue reading "The Universe"

 

 

What is a “Nebula”?

A Nebula is a cloud of gas and dust floating in space. It is visible either as a luminous region or a dark patch against the back ground of stars.

 

 

 

 

 

What is a Planetary Nebula?

A planetary nebula is a spherical or ellipsoidal shell of gas around a white dwarf, and is formed when a red giant leaves behind an outer shell of matter while contracting.

 

 

 

 

 

 

What are the Magellanic Clouds?

In 1519, Ferdinand Magellan the navigator observed two small star clouds in the heavens, similar to the Milky Way, visible to the naked eye. These have been named after him, and are visible only from the southern hemisphere. These clouds have since been identified as satellite galaxies of our own system.

 

What is the nature of the path traced by the Earth across the Universe?

The path of the Earth across the Universe is in an elaborate series of loops and whirling spirals. A person on the Earth’s surface would move in a path governed by:

1. Rotation of the Earth about its axis at 460 meters/sec at Equator.


2. Earth’s rotation about the barycentre of the Earth-Moon System.


3. Earth’s rotation about the Sun at 30 km/sec.


4. The sun’s rotation about the Milky Way Galaxy at 220 km/sec.


5. The Milky Way Galaxy’s rotation about the Local Group of Galaxies (LGOG) towards the constellation Hercules.


6. The rotation of the LGOG about the Virgo Super Cluster of Galaxies (VSCG) towards the constellation Southern Cross.


7. The rotation of VSCG about the Universe.

 

Of the above, only items 1 to 4 are clearly known. Items 5 and 6 are still speculative while item 7 is still unknown.

 

What are open star clusters?

They are clusters of stars. In galaxies, the stars are densely packed together, whereas in open star clusters the stars are not densely packed together but only loosely associated.

 

 

 

What are globular star clusters?

They are a spherically shaped cluster of stars. Typically, it contains about ten thousand to ten million stars apparently concentrated towards the centre.

Are globular star clusters visible to the naked eye?

Only two clusters are visible to the naked eye, through more than 120 can be observed with instruments.

 

 

 

 

 

 

To what cluster of galaxies does the Milky Way Galaxy belong?

It belongs to the Local Group of Galaxies which contains about 20 galaxies including the Milky Way Galaxy, the Andromeda galaxy and the two Magellanic Clouds.

How many galaxies are there in a cluster of galaxies?

Galaxies tend to form clusters containing up to a few thousand galaxies. The Local Groups of Galaxies is a relatively small cluster of galaxies.

 

 

 

Are galactic clusters visible to the naked eye?

Yes. The Pleiades and the Hyades are examples of galactic clusters visible to the naked eye.

 

 

 

 

 

 

 

How did galactic clusters originate?

Galactic clusters are thought to have originated from the fragmentation of large gas into smaller gas clouds which in turn have formed stars. All galaxies in a galactic cluster may therefore be assumed to be of the same age. Most galactic clusters are relatively young, perhaps a few tens or hundreds of millions of years pls.

 

 

 

 

 

 

 

 

 

To what super cluster of galaxies does the Local Group of Galaxies belong?

The Local Group of Galaxies belongs to the Virgo Super Cluster of Galaxies containing thousands of galaxies.

 

What portion of the universe is influenced by gravitational force?

Gravitational force is a form of force of attraction in the Universe. Every particle of matter exerts a gravitational pull on every other particle in the Universe.

Is gravitational force variable?

In 1687, the famous British scientist Isaac Newton proved that bodies having more mass exert greater gravitational pulls and as one moves farther from the centre of a massive body, the effect of such pull decreases. For example, a person standing on the surface of the Moon would weigh less than what weighed on Earth since the gravity on the Moon’s surface is less than that on the Earth’s surface. Also if he goes away from the Earth in a rocket, his weight will go on increasing.

 

 

 

 

What is the relationship between gravity, mass, weight and density?

Mass is the amount of matter that an object contains. All objects have mass. When gravity acts on a body, the body appears to have weight. As gravity increases, weight of the body also increases but the mass of the body remains unchanged. A stone weighing 1 kg and a pillow weighing 1 kg both have the same mass and therefore the same weight, but the stone has less volume than the pillow, because the material in the stone is more density than the pillow.

 

 

 

Continue reading "The Universe"

 

 

What is cosmology?

Cosmology refers to the study of the Universe as a whole, its origin, evolution and future development.

 

 

 

 

 

 

 

 

 

 

 

What is the “Cosmic Egg”?

The concentration of matter and energy prior to the Big Bang has been nicknamed as the ‘Cosmic Egg’ – an analogy with an egg which gives birth to life.

Will the Universe continue to expand?

If the mean density of the Universe is less than a certain critical value, the rate expansion should tend to remain steady and the Universe would expand forever.

If the density is greater than the critical value, the expansion will eventually slow down and cease, followed by a contraction phase. According to the Oscillating Universe Theory, the Universe expands and contracts in a cyclic manner repeatedly.

 Is the volume of matter so far detected in the Universe likely to exceed the critical value required to substantiate the Oscillating Universe Theory?

The volume of matter detected so far is below the critical value. However, there are various types of matter in the Universe about which we have incomplete knowledge e.g., inter-galactic matter and “invisible” matter.

 

 

 

What is meant by inter-galactic matter?

Inter-galactic matter refers to the rarefied matter that exists in the space between the galaxies. Its existence has not been proved by direct observation but indirectly by interfaces.

What are the basic constituents of the “matter” in the Universe?

Matter refers to material objects. The smallest unit of matter that can exist independently as a chemical element is the atom. Groups of atoms combined together are known as molecules. The atom itself consists of a core called the “nucleus” surrounded by an outer shell containing particles called electrons.

How large is the Universe?

The Universe apparently stretches out to an infinite distance. There is however a limit as to how far we can observe the distant objects with our naked eyes or even with instruments.

How did the Universe originate?

It is believed by most astronomers that all the matter and energy was once concentrated at one point and there was then a cataclysmic explosion in which matter and energy were scattered in all directions. The matter later coalesced into galaxies and other celestial objects to from the Universe as existing now.

 

 

What is the Big Bang?

The cataclysmic explosion at the time of the birth of the Universe has been nicknamed as the “Big Bang”. The analogy is to a bomb which bursts with a bang and scatters fragments at random.

Is there any observational evidence in support of the Big Bang theory of the origin of the Universe?

According to the Big Bang theory, there must be some very weak background microwave radiation across the Universe as are result of the Big Bang. In 1965, the manifestation of such microwave radiation approaching is from all directions was discovered thereby providing evidence in support of the Big Bang theory.

Is the Universe now expanding, shrinking or steady in volume?

Astronomical observations have inferred that the matter scattered by the Big Bang continuous to fly off in all directions confirming the continuing expansion of the Universe.