Our place in the universe

With a circumference of over 40,000 kilometres, the Earth feels very large. In relation to our solar system, our galaxy and beyond it is in fact tiny.

The sun and our solar system

Our solar system is made up of eight planets orbiting the sun. They are Venus, Mercury, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The planets were formed as a by-product of the birth of the sun around 4.5 billion years ago. There are over 100 billion stars like our sun in our galaxy, so could there be other planets like Earth?

There were until recently nine planets, but Pluto, a small body on the edge of the solar system has been re-classified as a dwarf planet . Our sun is a very ordinary star, known as a G2 class main sequence star. There are about 100 billion similar stars in our galaxy, the Milky Way.

An artist's impression of our home galaxy, the Milky Way © NASA

An artist's impression of our home galaxy, the Milky Way © NASA

Our galaxy

The Milky Way is like a spinning spiral disc with four arms. Our solar system is about two-thirds of the way from the centre along one of the arms, which is known as Pegasus . The galaxy's arms are where most of the dust and gases are concentrated and where most stars are born. The relatively flat arms spin at 250 kilometres a second around a bulging centre. This centre is thought to contain a supermassive black hole with a mass exceeding 50 times that of the sun that sucks in entire stars. The Milky Way is vast. It would take an object travelling at the speed of light (over 1 billion kilometres per hour), 51,000 years to travel from one side to the other.

The filament-like large scale structure of galaxies in the universe.

The filament-like large scale structure of galaxies in the universe.

Our universe

The Milky Way is the second largest galaxy within a cluster of 17 galaxies. Beyond our cluster are more clusters forming a honeycomb structure of interconnected filaments around large empty bubbles. This structure was probably set out soon after the Big Bang, which created the universe. There are thought to be about 100 billion galaxies in the universe.

Our place within the universe is very small and insignificant, but it is interesting because it supports intelligent life that can observe the universe and ask how it came to be there and why.

Cartoon image of a hatchet fish on a museum pass

Until 1938 whale carcasses were buried in the Museum grounds so that their flesh would decay leaving only the skeletons.