What is a black hole?

A black hole is a compressed dense mass with an intense gravitational field. The gravitational force of the black hole is so strong that nothing in its surroundings can escape from it, not even light. As a result, the space around a black hole gets distorted. It is similar to a gigantic funnel, which becomes flatter and flatter towards the upper margin. 

Everything near this funnel then slips down and makes the funnel deeper due to its own weight. The
black hole nearest to our solar system is about 8200 light
years away; so there is no real danger of being swallowed
by it.

 What is 'El Niño'?

'El Niño, which means 'the Christ Child' in Spanish, refers to a  disturbance in the Ocean current, which runs off the coast of Peru and which occurs every 3-8 years around Christmas. When distributed, the cold Humboldt current, which flows along the western coast of South America towards the north, is pushed back by warm water masses from southeast Asia. 

No one knows why this happens. The winds blowing over the Pacific also change dramatically during this disturbance; as a result, heavy rainfall and flooding Occurs in places that were earlier dry, while the hot and moist
regions experience such completely dry spells that fertile land dries up, crops wither, and people starve.

 How does a tsunami occur?

The Japanese word 'tsunami' means 'harbour wave'. It is a series of water waves caused by the displacement of a large volume of a body of water, usually an ocean,
though it can occur in large lakes. Tsunamis are caused by undersea landslides or by 'seaquakes', that is an earthquake whose epicentre lies below the ocean. 

If the seabed is displaced up to several metres, the water layer of several kilometres in thickness above it also moves with it. The wave caused by this movement has a lot of energy-much more than a wave of the same height whipped up by the wind. This becomes apparent when the wave moves towards the coast.

 How do we save ourselves from earthquakes?

Living in an earthquake-prone zone is often unavoidable. For instance, almost entire Japan lies in an earthquake-prone zone. For this reason, buildings here are primarily made 'earthquake resistant' so that the loss can be minimized. Buildings are built on foundations made of steel balls or from elastic materials such as bamboo. 

In skyscrapers, a pendulum weighing several tons is installed in the upper floors, which minimizes the vibrations that start in the upper storeys when an earthquake occurs. If an earthquake occurs, we should take refuge, at best, in the open or seek protection under a table.

 How are new seas formed?

Seas arise at places where the Earth's crust cracks open due to expansion. Around 200 million years ago the Atlantic was formed in this way. Today in East Africa, a crack from Malawi to Ethiopia has formed as a result of the eruption of a volcano. If the soil sinks further, water from the oceans will enter the region to give rise to a water body. 

This has already happened in the case
of Red Sea, the continuation of the East African rift system. If the plate continues to
expand, then at some point of time it breaks completely giving rise to a long mid-
ocean volcanic ridge.

 How are volcanoes formed?

Volcanoes are natural phenomenon that occur everywhere, but some places are more prone than the others. The molten rock and gas in the mantle called magma pushes its way upwards and pours to the surface through cracks in the crust. This is a volcano. There are different types of volcanoes; some are explosive others are not, and all erupt as spectacularly as we see on the television. Some eruptions take place unexpectedly, but others can be predicted, which is very important for the people living near a volcano.

 How were mountains formed?

Mountains are formed in two ways. When the tectonic plates move, they collide against each other. When the heavy oceanic part of the plate collides with the continental part, it submerges below it. The Andes, for instance, were formed in this way. The other way is when two continents collide with each other, the plates bend at the point of contact and fold up steeply. The Himalayas or the Alps were formed in this way around 35 million years ago and are counted among the 'young' mountains of the world. Old mountains, such as Black Forest or the Harz mountains, lower ranges because peaks have been wo down by rain, ice, and wind over time.

 What is the atmosphere made up of?

The word 'atmosphere' means a gaseous cover enveloping a planet. Without atmosphere life would not have been possible on the Earth: One-fifth of the atmosphere is oxygen and four-fifths is nitrogen. Like the Earth's interior, the atmosphere too is made up of several layers. All animals and plants live in the lowermost layer of the atmosphere called the 'troposphere'. 

All weather phenomena take place in the troposphere. Even aeroplanes fly in the outer edge of the troposphere. The stratosphere, the mesosphere, the ionosphere, and the exosphere lie above the troposphere.

 

How did we discover that the Earth is round?

About 30oo years ago people believed that the Earth was flat. But people wondered why ships disappeared at the horizon. Sailors too returned from journeys and were proof that ships did not fall off the edge of the Earth. 

The simplest explanation was: the Earth must be round. The final proof came in the year 1522 after the expedition of Ferdinand Magellan, who was the first to sail around the Earth.

What is the internal structure of the Earth?

 What is the internal structure of the Earth?

Like an onion, the Earth has several layers. The outermost layer, the Earth's crust, has an average depth of about 40 km. As compared with the diameter of the Earth, which is around 12,700 km, the Earth's crust is very small. It is primarily made up of solid rocks. 

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Below the crust is the mantle, reaching to a depth of about 2900 km. Due to the heat inside the Earth, the mantle consists of solid and molten rocks. Below the mantle is the core, made up of iron and nickel. The deeper one travels inside the Earth, the hotter it is. The temperature in the core is between 4000 and 5000°C.