Space is vast and full of wonders – let’s find out more about the endless universe
WHEN you look at the sky on a dark, cloudless night you can see countless stars and the moon. In the daytime you can see the sun rising and setting. We take a look at how the universe began and learn more about celestial bodies.
THE BIG BANG
Most astronomers believe the universe started about 14 billion years ago with a massive explosion – the Big Bang. They speculate that before the Big Bang the universe was just a tiny ball, a thousand times smaller than a needle’s point. But it was extremely hot and dense and suddenly exploded with immense force. The resulting Big Bang, scientists believe, was what created time, space and matter, and gave birth to the universe. In a split second the universe expanded, from being smaller than a single atom to becoming bigger than a galaxy – and according to science the universe continues to expand to this day at an incredible pace. Scientists base their theories in this regard on evidence such as the night glows or cosmic background microwave radiation from the Big Bang that can be observed with scientific instruments. American scientist Edwin Hubble (18891953) documented the movement of the galaxies in the 1920s. He determined that the speed of a galaxy is equal to its distance from Earth. This comparative rate is known as Hubble’s Law.
OUR PLACE IN SPACE
Centuries ago people thought Earth was at the centre of the universe and everything revolved around it – the sun, moon and stars. Today we know Earth and the other planets in our solar system move around the sun.
We also know that our solar system is part of a vast spiral-shaped galaxy known as the Milky Way.
There are scientists who think our solar system originated when large clouds of dust and gas imploded, causing a downward circular motion – like water washing down a drain. The sun and planets then emerged out of the mist (nebula).
THE MILKY WAY
Our solar system is located in one of the spirals of the Milky Way, a galaxy made up of billions of stars and their planets, as well as dust particles and gas. It resembles a giant whirlpool that turns at its centre once every 200 million years.
This galaxy is so vast that it takes light about 100 000 years to travel from one end to the other.
There are billions of other galaxies in the universe. OUR SUN The sun is massive and comprises about 98% of the matter (any substance that takes up space) in our solar system. Because of its enormous mass, the sun’s gravity is the strongest in our solar system and draws everything else towards it. But the planets also have their own gravity, which causes them to remain in set orbital paths around the sun.
The sun is the closest star to Earth and emits life-giving sunlight and heat. But sunlight also contains potentially harmful ultraviolet rays that can cause sunburn and skin cancer. The sun is actually a huge ball of super-hot gas some 1,4 million km in diameter (the size of 109 Earth-sized planets placed next to one another). Its mass is equal to 330 000 Earths, and about 1,3 million Earths could fit inside it.
Looking at it from Earth the sun might not seem that big, but remember it’s about 150 million km from us. At this distance it takes sunlight (at a speed of about 300 million m/sec) about eight minutes to reach us. THE PLANETS In addition to the sun, our solar system consists of eight main planets. The four rocky ones closest to the sun – Mercury, Venus, Earth and Mars – are relatively small.
Beyond Mars there’s an asteroid belt – a collection of rocky objects and space debris left over after the planets were formed.
Beyond this rocky belt we find the four gaseous giants – Jupiter, Saturn, Uranus and Neptune. Although much bigger than Earth, these planets are relatively light in weight because they’re made up mainly of hydrogen and helium gas.
Pluto, an icy world on the outskirts of our solar system, is regarded as a dwarf planet because it’s considerably smaller than our moon. THE MOON Earth’s natural satellite, the moon, is made of rock. The moon’s orbit around Earth takes 27 days, but the moon also takes 27 days to make a full turn on its own axis. Because Earth also turns (on its own axis as well as around the sun) it seems to us like the moon’s orbit around Earth takes 29 days. The moon’s gravity is responsible for ocean tides on Earth.
Scientists believe the moon originated 4,5 billion years ago when Earth was created. They speculate a massive rock collided with our newly formed planet, slicing off a part of it which then became the moon.
The moon doesn’t have an atmosphere (layer of gas and liquid) around it to protect it against comets and meteors, or radiation from the sun. It therefore gets extremely hot and cold.
Earth’s atmosphere causes most incoming meteors to burn out before they can hit the ground, but on the moon meteorite strikes can cause huge craters. Its surface is covered in a dust layer about 5cm thick. This dust probably comes from space or is the result of the impact of meteorites.
An artist’s impression of the WMap (Wilkinson Microwave Anisotropy Probe) spacecraft that was used to measure the night glow or cosmic microwave background radiation between 2001 and 2010 to help scientists understand more about the Big Bang.
The Milky Way galaxy has between 100-400 billion stars (including our sun), but when you look up into the night sky the most you can see is about 2 500. The heat and light from our sun come from nuclear fusion, quite a different process to that of fire...