The Universe
The Universe is everything that exists – all of space, matter, energy, and time. It is a huge wide-open space with billions of galaxies, each containing billions of stars, and yet it is at least 99.99 per cent empty space. It has been expanding constantly since its beginning 13.8 billion years ago, when it exploded into life with the “Big Bang”.
GALAXIES
Galaxies are huge groups of stars, and they can be seen in the night sky using a telescope. They come in lots of different shapes, and most of them are thought to have a massive black hole at their centre.
STARS
Stars are classified into different types depending on their temperature and brightness. Scientists use the Hertzsprung-Russell graph (shown below) to compare the size, temperature, and brightness of individual stars.
PLANETS
Planets are large, spherical objects that orbit a star. In our Solar System, there are eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Planets that occur outside our Solar System are known as exoplanets.
The Universe is everything that exists – all of space, matter, energy, and time. It is a huge wide-open space with billions of galaxies, each containing billions of stars, and yet it is at least 99.99 per cent empty space. It has been expanding constantly since its beginning 13.8 billion years ago, when it exploded into life with the “Big Bang”.
GALAXIES
Galaxies are huge groups of stars, and they can be seen in the night sky using a telescope. They come in lots of different shapes, and most of them are thought to have a massive black hole at their centre.
NEBULAE
Nebulae are the “nurseries” of the Universe – they are huge clouds of gas and dust in which stars form. They may be trillions of kilometres wide and many have amazing shapes and colours.
Stars are classified into different types depending on their temperature and brightness. Scientists use the Hertzsprung-Russell graph (shown below) to compare the size, temperature, and brightness of individual stars.
STAR TYPES
Most of the stars, including our Sun, are found along a part of the
graph called the Main Sequence. As they age, these become giants
or supergiants, and then dwarfs or supernovas.
BLACK HOLE
A black hole is a region of space where matter has collapsed in on itself. This means there is nothing to be seen, but astronomers know black holes exist because they have such a strong gravitational pull that nothing can escape them – not even light.
MOONS
A moon is a rocky body that orbits a planet. Some planets have many moons but Earth has only one. Moons are also known as natural satellites.
DWARF PLANETS
Large planets have enough self-gravity to make them form into a round shape as they move through space. Smaller planets that cannot do this, but do orbit the Sun, are called “dwarf planets”. Pluto is one of the largest dwarf planets in our solar system.
PLANETS
Planets are large, spherical objects that orbit a star. In our Solar System, there are eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Planets that occur outside our Solar System are known as exoplanets.
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