How big is the Universe?

If you look at the sky at night, you will see an incredible amount of stars out there. It seems almost unfathomable how many there are. But what you can see is only the tip of the iceberg: it's not even that many in the great scheme of things. All of the stars that are visible to the naked eye belong to our own galaxy, the Milky Way.

A galaxy is hundreds or thousands of millions of stars, all collected together, and all gravitationally interacting and orbiting around a common point. Since the beginning of the 19th century, astronomers have identified more and more new galaxies. Early discoveries were through photographic evidence: galaxies at enormous distances from Earth appeared so tiny that they could hardly be distinguished from stars, but nevertheless they were galaxies. The largest galaxy we have discovered is thought to have around 13 times as many stars as the Milky Way!

Galaxies usually cluster together in groups, which then form large clusters of galaxies. Our galaxy is part of a small cluster of about 40 others that astronomers have now called the Local Group. The Milky Way and the Andromeda Galaxy are thought to be the 2 largest, each having about 100-200 billion stars.

Astronomers estimate there are 50 billion galaxies in our universe; we can only see 400 million galaxies with a telescope. Each of those galaxies, if they were similar to ours, would have 400 billion stars in them. That means potentially 160,000,000,000,000,000,000 stars!

Did You Know ... ?

So, with all those stars, and all those galaxies, just exactly how big is the universe? Perhaps we can only truly find out by leaving the Milky Way and exploring what lies beyond.

Can we travel 'beyond'?

We have made many attempts at going into space since the start of the space age in 1957 with the Russian launch of Sputnik 1, and the American Explorer 1 in 1958. The National Aeronautics and Space Administration (NASA) was created in the USA in 1958, and since this time there have been over 3,000 launches of space vessels of all kinds. Most of these have been launched into the Earth's orbit, but 12 men have walked on the moon, and there are several thousand objects circling the Earth as a result of launched vessels – mostly parts of space-launch vehicles.

But going beyond the Earth's atmosphere is a challenge. Spacecraft must orbit in order to remain in space so they must use rockets for propulsion and movement. There is also no air or oxygen: it is a hostile environment to human beings. The vacuum of space would destroy a human body in a matter of seconds by decompression! Temperatures in the shadow of a planet would be very cold, whilst exposure to the Sun's radiation would be fatal. Weightlessness is another factor and there are many studies into the long-term effects this has on a human. All of this must be taken into account when travelling in space.

Launch it ... What would happen to the environment of a planet if you changed its gravity and temperature? Have a look at planet x...

One way of enhancing our knowledge, and increasing the potential for manned missions to space is to launch unmanned vessels, called space probes. Space probes have provided a vast source of information on the nature of the Solar System and the origin of the Universe by radio-transmitting information back to Earth. The early artificial probe, Sputnik 1, was destroyed by friction heat when it re-entered the Earth's atmosphere, but there have been many more since. There have been many unmanned lunar missions, for example, the American missions, Surveyor and Lunar Orbiter in the 1960s, and the Russian Luna missions in the 1970s.

There have been many planet studies as a result of space probes too. Spacecraft have landed on Mars, Venus, and have flown by every planet in our Solar System except for Pluto and we have even made comet studies using them.

Did You Know ... ?

Russia made history in 1961 by launching the first man into space; Yuri Gagarin made history when he orbited the earth in Vostok 1. The first man to walk on the moon was Neil Armstrong, who made “one small step for man, one giant leap for mankind” in 1969 as part of the Apollo 11 mission. The Apollo programme has continued to send men to the moon with successful missions on Apollo 12, Apollo 15, Apollo 16 and Apollo 17.

In the early 1980s, a space shuttle was launched by the American Space Transportation System called Challenger. This was a manned space-plane designed to carry new satellites out into space and to repair old satellites. At the same time, the European Space Agency was launching satellites through its unmanned Ariane programme. Challenger met with disaster in 1986, when the craft exploded minutes after launch. Plans resumed with Discovery, which launched in 1988, which placed a satellite, TDRS-3 into orbit. In 1990, the Hubble Space Telescope was deployed, but because of a defect, it was fully functional in 1993.

So what does the future hold for space exploration? There are plans for a manned space station, and the construction of the X-30 – a spacecraft designed to take off on a usual runway, but using a ramjet engine to boost itself into orbit. Plans are already afoot to create a permanent lunar base, and the exploration of other planets, such as a mission to Mars, are in progress.

Did You Know ... ?
Discuss it ... Do you think we will ever travel beyond our Solar System?
Teachers' Notes ... For Teachers' Notes on this subject, click here.