When you look into the blackness of the night sky, you are peering into the fathomless depths of the Universe. Stars, Planets, and Galaxies stretch into space not just further than you can see, but further than you can imagine.
The Universe is the whole of existence – all of space, matter, energy and time. The Universe is so vast as to be unimaginable, but we do know that it is steadily expanding following it’s beginning 13.8 billion years ago in an explosive event called the Big Bang.
Understanding The Universe
People used to think of the Universe as a giant sphere, but we know that things are not so simple. The Universe probably has no center or outer edge. Only a fraction of it – the observable Universe – is visible to us. The whole Universe may be vastly bigger than this, perhaps infinitely so.
The Shape of space
The three dimensions of space are “bent” by the force of gravity from matter in the Universe into a fourth dimension that we can’t see. This is hard to visualize, so scientist use the metaphor of a two – dimensional rubber sheet to explain the idea. The mass of the Universe could bend this rubber sheet in one of three ways, depending on how densely packed with matter the Universe is. Most scientist now think the shape of the Universe s “flat”.
FLAT : Just the right amount of matter would give the Universe a flat shape. This would also be infinite in size with no outer edge.
OPEN : If the Universe isn’t dense enough, it might stretch into an “open” shape, making it infinite in size with no outer edge.
CLOSED : A dense Universe would bend itself into a closed shape. Travelling in a straight line would bring you back to your starting point.
THE SCALE OF SPACE
The Universe is so vast that we cannot appreciate its size without making leaps of scale. In this series of pictures, each stage represents a microscopic speck of the image to its right. When dealing with the vast distances in space, kilometers aren’t big enough. Instead, astronomers use the speed of light as a yardstick. Light is so fast it can travel around Earth 7.5 times in a second. One light year is the distance light travels in a year: nearly 10 trillion km(6 trillion miles).
Earth and Moon
Earth is 12,756 km (7,926 miles) wide. Our nearest neighbor in space – the Moon – orbits Earth at a distance of 384,400 km (238,855 miles). If Earth were the size of a football, the Moon would be the size of a melon about 21 meters (69 ft) away.
The Sun’s family of eight plants occupy a region of space 9 billion km (5.6 billion miles) wide. If Earth were a football, it would take five days to walk across this part of the Solar System. The nearest star would be a 58 – year walk away.
The nearest star to the Sun is Proxima Centauri, which is just over four light years away. There are around 2.000 start within 50 light years of the Sun. These make up our stellar neighborhood , which is a tiny fraction of the Milky Way Galaxy.
Milky Way Galaxy
The Milky Way is a vast cloud of 200 billion stars. Its shape resembles a pair of fried eggs held back to back, with a central bulge surrounded by a flat disk. It measures 100,000 light years across the disk and 2,000 light years deep through the bulge.
Local Group of Galaxies
The Milky Way is just one of perhaps seven trillion galaxies in the observable Universe. Galaxies exist in groups called clusters, held together by gravity. The Milky Way is part of a cluster known as the Local Group, which is about 10 million light years wide.
Clusters of galaxies exist in even larger groupings called super clusters. We live in the Virgo Super cluster, which is one of millions of super clusters in the known Universe. Between these are immense empty areas called cosmic voids.
Super clusters are thought to form a vast web of filaments riddled with enormous voids containing no galaxies. The true size of the Universe is a mystery, and only a fraction of it is visible to us. The Universe may even be infinite in size.