Technology

The first telescopes were developed by a Dutch spectacle maker called Hans Lippershey around 1608. The idea was seized upon by Galileo Galilei, who built his own telescope to watch the skies and make his ground-breaking observations.

The earliest telescopes used refraction or the bending of light to magnify images. Two convex lenses – bulging pieces of glass – are placed inside a tube. Light enters the telescope in parallel lines. As it passes through the first lens – known as the objective lens – it bends.

The rays start converging together, to a focal point, where the rays cross each other and start to move apart again. After the rays diverge, a second lens is put in their path to straighten them out again.

This second lens is known as an eyepiece lens, and creates an image on your retina. Your eye is tricked into thinking that you’re looking at something much closer than it really is.

While the earliest telescopes used a pair of lenses to gather light, most modern telescopes use mirrors. This is because it's much easier to produce a large mirror than a large lens – and size is important, as it allows a greater level of magnification.

Astronomers refer to lens-based telescopes as refractor telescopes, and mirror-based ones as reflector telescopes.

Reflector telescopes can be colossal. The Extremely Large Telescope, currently under construction in Chile, will include a mirror with a diameter of 39.3 meters. Making a lens of that size would not really be feasible.

One of the biggest challenges for modern telescopes is light pollution. Sky glow – the brightening of the night sky – reduces the contrast between the sky and objects such as stars or galaxies.

Telescopes also need to contend with the blurring effects of the atmosphere. Turbulence and particles in the atmosphere can distort the picture of the sky we get from Earth. You can see this effect with the naked eye while looking up at the night sky. It's what makes the stars appear to twinkle.

But there's a solution to all this. Instead of using our telescopes down on Earth, we can send them up into space.

NASA launched the first successful space telescope in 1968 – the Orbiting Astronomical Observatory (OAO-2). It was used to detect ultraviolet radiation and, among other things, confirmed that massive clouds of hydrogen surround comets.

Since then, there have been more than ninety telescopes successfully sent into space.

Space telescopes do have their drawbacks. They’re expensive to build and launch, and once they’re up into space, they're hard to maintain and repair. But this trade off is often worth it. Space telescopes give us much better data than anything we could get from a ground-based telescope on Earth.

Telescopes aren't only used to gather visible light. They're also used for other parts of the electromagnetic spectrum.

When a telescope is used for visible light, we call it an optical telescope. It's very different to something like a radio telescope, which uses large metal discs to collect radio waves. Microwave telescopes, infrared telescopes, ultraviolet telescopes, X-ray telescopes, and gamma ray telescopes have also been developed, each using different techniques.

They also offer another reason to use space telescopes rather than ground-based telescopes. The Earth's atmosphere blocks a large chunk of the electromagnetic spectrum, including most ultraviolet light, and all X-rays and gamma rays. To measure these, the only option is to send telescopes up into space.

Between 1990 and 2003, NASA launched four ambitious space telescopes, each one designed to detect radiation from different parts of the electromagnetic spectrum. Together, these telescopes became known as the Great Observatories.

The four telescopes were the Hubble Space Telescope, the Compton Gamma-ray Telescope, the Chandra X-ray Observatory, and the Spitzer Space Telescope.

The Compton Gamma-ray Telescope operated from 1991 to 2000 and detected x-rays and gamma-rays. The Spitzer Space Telescope operated from 2003 to 2020 and detected infrared radiation.

The Hubble Space Telescope, and the Chandra X-ray Observatory, are still in operation.

The Hubble Space Telescope, launched in 1990, is probably the most famous of the Great Observatories. It observes a range of electromagnetic radiation from near-infrared, through visible light, and into ultraviolet.

It has made more than 1.5 million observations, and, among other things, helped to detect the universe's accelerating expansion.

As for the Chandra X-ray Observatory, it's used to detect x-rays from sources billions of light years away. In particular, it examines very hot, turbulent regions of space to answer fundamental questions about the universe's origin.

Since the Great Observatories, more and more telescopes have been put into space.

The Kepler Space Telescope was launched in 2009, and used to search our galaxy for habitable planets. It retired in 2018, but not before it had discovered more than 2600 planets.

The Wilkinson Microwave Anisotropy probe (WMAP) mapped irregularities in the background microwave radiation of the universe. It operated between 2001–2010, and was succeeded by the Planck Observatory of the ESA, which ran between 2009–2013.

More recently, in 2021, the James Webb Space Telescope (JWST) was put into space. It's one hundred times more powerful than the Hubble Space Telescope, and designed to detect infrared radiation more precisely than ever before. To do this, the telescope uses a huge mirror – 6.5 meters in diameter."

The JWST is used to study the formation of the very first galaxies and stars in the universe.

One of the first images released is the deepest and clearest image we have ever had of the distant universe. Packed with thousands of distant galaxies, this deep-field image by the telescope covers a tiny patch of sky – about the size of a grain of sand held at arm’s length. It’s a breathtaking reminder of the scale of the universe.

As the JWST continues to operate, we will receive more data and images that reveal the extraordinary secrets of the universe.

Telescopes aren't the only way for astronomers to study the universe. Over the last few decades, they've also sent a number of spacecraft into space.

During launch, spacecraft take rocket-powered flights that reach extremely high speeds. They need to fly through the Earth's atmosphere and reach escape velocity. Escape velocity is the minimum velocity that an object needs to reach in order to escape the gravity of a larger object, like a planet.

The heavier an object, the harder it is to get it up into space. Because of this, unmanned spacecraft are generally more viable than manned spacecraft. The technology needed to support a human adds a lot of extra weight.

In 1997, the Cassini probe was sent to investigate Saturn and its moons. It was the result of a collaboration between NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI).

The Cassini mission gave us valuable information. For example, we learned that Enceladus, an icy moon of Saturn, has oceans of salty liquid water hiding beneath its surface. Jets from these oceans spray into space, and Cassini was able to directly sample one of these plumes. This sample revealed a cocktail of organic materials, water vapor, carbon dioxide, carbon monoxide, and volatile gases.

At the end of its mission, Cassini crashed into Saturn in a ‘grand finale’. During its final dive, it sent data back to Earth for as long as it could. It burned up in Saturn’s atmosphere shortly after it stopped transmitting data.

Hayabusa was a robotic spacecraft developed by the Japan Aerospace Exploration Agency (JAXA) and launched in 2003. It traveled to the 25143 Itokawa Near-Earth asteroid, where it retrieved samples of materials to return to Earth.

Hayabusa was the first spacecraft designed to land on an asteroid and take off again afterward. Originally, the plan was to briefly touch the asteroid, but it ended up lingering for around 30 minutes instead.

The mission delivered the first sample of an asteroid that we’ve ever seen on Earth. It's the kind of triumph that would only be possible with the help of an unmanned craft.

Another important example of unmanned craft are the Mars rovers. These robotic vehicles are designed to explore Mars' surface.

The first successful Mars rover was Sojourner, launched in 1996 and designed to demonstrate that scientific equipment could be sent to Mars at a relatively low cost.

Opportunity and Spirit were both launched in 2003. Evidence from both suggested that there used to be water on Mars – possibly enough to sustain life.

Today, three more rovers – Curiosity, Perseverance, and Zhurong – are all active on Mars. Curiosity was launched in 2011, Perseverance was launched in 2020, and Zhurong was launched by the Chinese National Space Administration in 2020. Zhurong is being used to collect some general environmental data, including information on the magnetic field of the planet.

Manned missions into space are harder and more expensive than unmanned missions. But that doesn't mean they can't happen.

In the 20th century, space exploration was changed forever by the politics of the Cold War, and the space race between the United States and the Soviet Union.

In 1961, Yuri Gagarin became the first man to orbit the Earth. And in 1969, the Apollo 11 mission put the first ever humans on the moon. Both of these were incredible accomplishments. Just a few decades earlier, the thought of putting humans into space was almost unimaginable.

Perhaps the greatest example of a manned spacecraft is the International Space Station (ISS). Five space agencies are involved: NASA, ESA, JAXA, the Canadian Space Agency (CSA), and Russia’s space agency (Roscosmos).

The ISS is used as a space research laboratory, where experiments can take place under microgravity and in the environment of space. At 109 meters from end to end, the structure is absolutely huge. It’s been continuously occupied for over 20 years, ever since 2000.

A huge range of fields are represented in the experiments carried out aboard the ISS – from materials science to space medicine. For example, the Alpha Magnetic Spectrometer-02 docked on the ISS looks for evidence that could help us identify dark matter, and understand the formation of the universe.

Government-funded organizations have driven the history of manned spacecraft. But private companies such as SpaceX are now starting to make an impact.

Already, SpaceX is working with NASA to fly people to the ISS. And they also have some bold ambitions to send humans to Mars, and establish some kind of research colony.

Maybe, one day, humans will be able to travel even further, leaving the solar system behind and visiting other stars. What else could we discover about the wider universe if we were able to strike out and explore it?

Astronomy is one of humanity's oldest sciences. But one thing is certain: there's still so much to learn.