The Universe is everything we can see, touch, feel, sense, measure or detect. It includes living things, planets, stars, galaxies, dust clouds, light, and even time. Before the birth of the Universe, time, space and matter did not exist.
There are billions of galaxies in the
Universe, galaxies are made of millions of stars. Perhaps, most of
these stars have planets around them, just like our Solar System. The
space between galaxies is almost empty: only few atoms of hydrogen
per cubic centimeter. Space also has radiation, like the light and
heat, magnetic fields and high energy particles,
The Universe is incredibly huge. It
would take a modern airplane more than a million years to reach the
nearest star to the Sun. Travelling at the speed of light (300,000 km
per second), it would take 100,000 years to cross our Milky Way
galaxy alone.
No one knows the exact size of the
Universe, because we cannotsee the edge – if there is one. The
Universe has not always been the same size. Scientists believe it
began in a Big Bang, which took place nearly 14 billion years ago.
Since then, the Universe has been expanding outward at very high
speed. So the area of space we now see is billions of times bigger
than it was when the Universe was very young. The galaxies are also
moving further apart as the space between them expands.
As you have read the Universe is so big that we need new units of measurement; Two of them are the light year and the astronomical unit. What is a light year? What is an astronomical unit?
(Adapted from ESA Kids.)
As you have read the Universe is so big that we need new units of measurement; Two of them are the light year and the astronomical unit. What is a light year? What is an astronomical unit?