Category Astronomy

What is Galaxy?

GALAXIES

           Galaxies are gigantic collections of stars. The galaxy in which the Sun is situated, the Milky Way Galaxy, is a vast spiral of about 200 billion stars measuring about 100,000 light years across. There are billions more galaxies in the Universe, most of which are elliptical (oval) in shape. There are also others that have irregular shapes.

            The Milky Way has a bulge at its centre, the nucleus, where older red stars are concentrated. Four giant arms radiate out from the nucleus. These contain younger blue stars as well as areas of gas and dust – the raw material for the creation of new stars. The whole spiral spins at a speed of about 250 kilometres per second.

            The Milky Way Galaxy closely resembles the Andromeda Galaxy, which lies 2.25 million light years away. The Sun is situated on one of the spiral arms about halfway out from the nucleus. Here are mostly yellow and orange young-to-middle aged stars.

            The Horsehead Nebula is really a gigantic cloud of dust and gas that has taken on a familiar shape. It is one of many clouds in our Galaxy where stars start to form.

Picture Credit : Google

What is Big Bang Theory?

BIG BANG

Many astronomers believe that the Universe began life in a single momentous event. This was an incredibly hot, dense explosion called the Big Bang, which took place about 15 billion years ago. During this explosion, all matter, energy, space – and time itself – were created.

In the first few millionths of a second, the particles that make up atoms, the building blocks of all matter, were formed. It took about 100,000 years for the first atoms, those of the gases hydrogen and helium, to come together. By this time, the searing heat of the Big Bang had cooled, space had expanded and the gases began to spread out. Gradually, however, gravity drew the gases together, leaving vast regions of empty space in between.

About a billion years after the Big Bang, the clouds of gas started to form into galaxies. Matter inside the galaxies went on clumping together until stars were created. Our own Sun was born in this way about 5 billion years ago. Its family of planets, including our Earth, was formed from the debris spinning round the infant Sun. With billions and billions of stars and planets forming in the same way across the Universe, it seems almost certain that life will have also evolved elsewhere. Will we on Earth one day make contact with these alien life-forms?

The expansion of the Universe is slowing down. Some astronomers think that gravity may eventually bring the expansion to a halt, then collapse all matter once more to a single point in a “Big Crunch”. Others believe that there is not enough material in the Universe to do this and that the Universe will carry on expanding forever.

Many scientists think that all matter in the Universe will eventually collide: the “Big Crunch”. Vast amounts of invisible “dark matter” in the Universe may exert sufficient gravity to halt its expansion and cause the galaxies to compress together.

Picture Credit : Google

What is Universe?

UNIVERSE

Everything that we can think of and everything else that exists – all belong to the Universe. From grains of sand to tall buildings, from particles of dust to giant stars and planets, from microscopic bacteria to people – all are part of the Universe. It even includes empty space.

The Universe is unimaginably vast: billions upon billions of kilometres wide. Distances in the Universe are so great that we have to use a special measure to record them. This is a light year, or the distance that light, which moves at a speed of about 300,000 kilometres per second, travels in one year: about 9,460,528,405,000 kilometres. The nearest star to Earth (after the Sun), Proxima Centauri, is 4.2 light years away. The most distant objects we know in the Universe are more than 13 billion light years away from Earth.

Nearly all the matter in the Universe is contained in galaxies, enormous masses of stars, has and dust. There may be about 100 billion galaxies, each containing hundreds of billions of stars. Galaxies are grouped into giant “clouds” of galaxies, called superclusters. These are spread round the Universe like a net, made up of strings and knots. In between there are gigantic empty spaces.

The superclusters are, themselves, made up of smaller clusters of galaxies. One of these, a cluster of 30 galaxies or so, is called the Local Group. It contains the Milky Way Galaxy, the vast spiral of stars to which our own local star, the Sun, belongs.

Astronomers have discovered that all galaxies are rushing away from one another. This means that, a long time ago, they were once all close together. So the Universe had a definite beginning – and may have an end.

The Universe is composed of many galaxy superclusters, themselves made up of clusters of galaxies. One of these contains the Milky Way Galaxy, a spiral-shaped mass of about 200 billion stars, one of which is our own Sun, parent to a family of nine planets.

The third planet from the Sun is Earth, orbited by the Moon. Earth is the only world in the Universe where life is known to exist, but we may discover others one day.

It is possible that the Universe will carry on expanding forever. In this sequence, the Universe is created in an immense explosion called the Big Bang. It expands rapidly, with all the galaxies moving away from one another as the Universe inflates like a balloon.

Picture Credit : Google

Why does moon has thousands of craters?

A crater is formed when a small space body such as an asteroid or a meteor collides with the surface of a planet or a moon. The Earth and the Moon both have many craters but the chances of Earth being hit by a space body is far more than the Moon due to its large size. However, despite its size, the moon has thousands of craters while we know of only 180 on Earth. Why?

Both Earth and Moon have been hit many, many times by small space bodies throughout their existence. However, the Earth has processes that can erase almost all evidence of a crater, unlike the Moon. The three processes are:

Erosion

The Earth has water (rain, floods), plants (break up earthen materials) and weather (wind, etc.) which can act together and erode over a period of time erosion can break a crater down to almost nothing.

The Moon on the other hand has no erosion because it has no atmosphere. This means it has no wind, no water and definitely no plants that can erode its surface and remove marks off its surface.

Tectonics

Tectonics are processes that cause Earth’s surface to form new rocks and get rid of old ones due to their shifting around over millions of years. Because of this, Earth’s surface is recycled many times throughout its existence, leaving it with very few rocks that are as old as those on the Moon. Since the Moon has not had tectonics for billions of years, it has a lot of time to stay put.

Volcanism

Volcanic flows on Earth can cover up impact craters. This is also the way may impact craters get covered in other parts of the solar system. While the Moon had large volcanic flows in the past that covered up most of its craters, it hasn’t had volcanism in nearly three billion years!

 

Picture Credit : Google

Which are the two famous impact craters on earth?

Apart from planets, stars and moons, there are several small solar system bodies such as asteroids and comets in space. These are usually speeding through space. Sometimes, a larger body such as a planet or a moon can come in their way. When this happens, these extremely fast spacebodies crash into the surface of the larger space body and create a depression called impact crater.

For an object to be able to create an impact crater, it needs to be travelling at a speed of many thousand kilometres per hour. No matter how hard or tough the surface of a planet or the moon is, when a superfast object collides with it, it will definitely leave an impact by vaporizing the area and creating enormous shockwaves through the ground, which can melt and recrystallise rock.

The size and shape of a crater depends on factors such as mass, density and velocity of the impacting object, and the geology and velocity of the impacting object, and the geology of the surface it strikes. Many planets and moons in our solar system have impact craters.

Two of the famous impact craters on Earth are:

Meteor Crater

Also known as the Barringer Crater in Arizona, the U.S., this is the first crater formed by an extraterrestrial impact to be identified. It formed nearly 50,000 years ago from a meteorite that may have been up to about 150 feet wide travelling at more than 45,000 kmph.

Vredefort crater

Situated in South Africa, this is the largest-known impact crater on Earth. It is nearly 300 km in diameter and over two billion years old. However, due to erosion over time, it is difficult to see the crater. What remains today are geological structures at its centre known as the Vredefort Dome or Vredefort impact structure.

 

Picture Credit : Google

How astronauts live in space station?

The International Space Station (ISS) is the biggest object ever flown in space. It orbits at around 400 km (250 miles) above Earth and a team of astronauts have lived and worked here since the year 2000. It is our first step towards exploring deeper into the Solar System.

Experiments

Astronauts do lots of scientific experiments on the space station to help us understand more about the effects of living in space. This will be useful knowledge for future deep-space exploration.

Canadam2 is a robotic arm that moves equipment around the ISS. Science experiments are carried out in the Columbus laboratory. The Japanese Kibo laboratory has a mini airlock, so astronauts can put experiments outside. Oxygen is generated in the Tranquility module. The Soyuz capsule carries people and supplies to and from the ISS.

Keeping fit

There is no gravity in space, so astronauts exercise every day. It keeps them healthy and stops their muscles from getting weak.

Spacewalk

Sometimes astronauts have to go outside on spacewalks to repair the ISS. They wear special suits to protect them from the harsh environment of space.

Nice view

From the space station you can see entire countries, storms from above, and 16 sunsets and sunrises every day!

Robonaut

Robonaut 2 is a NASA (US space agency) robot astronaut that lives in the space station and helps the crew with simple tasks, such as changing air filters. Its head has cameras, which work like eyes, and its hands can operate simple tools.

 

Picture Credit : Google