Astronomers studying space have two big problems:
- A lot of things in space seem invisible – they do not give out light we can see.
- Scientists cannot leave the Earth to go and collect pieces of stars and galaxies to study.
Using different wavelengths of light
There are special telescopes and other instruments that can detect light we cannot see with our eyes. Look up into the sky at night. Just with your eyes, you can often see the Moon, planets, stars – even a couple of galaxies outside the Milky Way. With a telescope, you can see a lot more – fainter and more distant stars, dust clouds, galaxies.
But there is a lot you can’t see, even with a powerful telescope, because not everything in space gives out light we can detect with our eyes. Some space objects give out X-rays, ultraviolet radiationradio waves and other parts of the electromagnetic spectrum. These wavelengths of light can be detected with special instruments. Find out more about these instruments in the article Light and telescopes.
Studying stars from a distance
Stars and galaxies are too far away for us to send spacecraft to collect samples to study. Space probes have visited other planets in the Solar System and the Sun, but other stars are too far away. Even if a spacecraft travelled at 100,000 kilometres an hour, it would take over 46,000 years to reach the nearest star outside the Solar System, Proxima Centauri. It would take another 46,000 years to bring a sample back. It would take 27 billion years to reach the nearest galaxy outside the Milky Way. The article Distances in space relate some of these huge differences to smaller ones we know better.
The light of the electromagnetic spectrum is the key to finding out about space without leaving Earth. By studying the different wavelengths of light given off by objects in space, astronomers can find out such things as what the objects are made of, how hot they are, how old they are, what gravity they have, how they are changing and much more.
New Zealand astronomers
There are a number of astronomers in New Zealand, and on this website you can find out about how two of them - Associate Professor Melanie Johnston-Hollitt and Professor Denis Sullivan - use the electromagnetic spectrum to:
- find planets around other stars
- predict the story of our Sun by studying distant white dwarf stars
- investigate galaxy clusters to help understand the structure of the universe.
Astrophysics – the new astronomy
‘Astronomer’ is not the best word used to describe these scientists any more. There is so much physics and chemistry involved these days (gravity, light, chemical elements and reactions, temperature, mass, energy and so on) that these scientists are called astrophysicists rather than just astronomers. Some of them try and work out the structure of the universe as a whole – they are called cosmologists.
We can learn a lot from the way astrophysicists carry out their science. They make measurements, collect lots of data, think about what the data means and make predictions. They can’t see the actual matter that makes a star, but they can predict what it is like. They can’t see a black hole, but they can predict what it is like by the way it affects things around it. Astrophysicists often use mathematics and computer models in which they try to match their observations with what is already known about physics. So many physics experiments have been done in laboratories on Earth that they can be fairly confident that their models are accurate.
Take up the challenge
Student activites simulate some of the work carried out by astrophysicists.
In Hunt the planet, students plot graphs of light measurements from stars, searching for dimming that indicates the presence of a planet, and calculate its size.
Is anything out there? asks students to consider evidence for life and examine data to decide on the likelihood of life on certain extrasolar planets.
In Shrink the solar system, students create a scale model of the Solar System and use a range of measurements, from mm to light years.
For explanations of key concepts, see Space revealed – key terms.
Check out a timeline explaining the history of planet hunting - from the discovery of the Solar System's outermost planets to extrasolar planets.