On July 11, the James Webb Space Telescope (JWST) made history by releasing its debut image: a jewel-filled photo touted as the deepest photograph of the Universe ever taken.
Aside from looking further out into space than any observatory before it, the James Webb Space Telescope has another trick in its mirror: it can look further back in time than any other telescope, observing distant stars and galaxies as they appeared 13.5 billion years ago, not long after the beginning of the universe as we know.
How is that possible? How can a machine look “into the past”? It’s not magic; It’s just the nature of light.
“Telescopes can be time machines. Looking into space is like looking into the past,” NASA scientists said WebbTelescope.org (opens in new tab). “It sounds magical, but it’s actually quite simple: light takes time to cross the vastness of space and reach us.”
gallery: First photos from the James Webb Space Telescope
All the light you see – from the twinkling of distant stars to the glow of your desk lamp a few feet away – takes time to reach your eyes. Luckily, light travels amazingly fast – about 670 million miles per hour (1 billion km/h) – so you’ll never notice it travel, say, from your desk lamp to your eyes.
However, when you look at objects that are millions or billions of miles away – like most objects in the night sky – you see light that has come a long, long way to reach you.
Take The sun, for example. Earth’s home star is an average of 93 million miles (150 million kilometers) away. This means that light takes about 8 minutes and 20 seconds to travel from the sun to earth. So if you’re looking at the sun (although you should Never look directly at the sun (opens in new tab)), see it as it appeared more than 8 minutes ago and not as it appears now – in other words, you are looking 8 minutes into the past.
That Speed of Light is so important to astronomy that scientists use light-years instead of miles or kilometers to measure great distances in space. A light year is the distance that light can travel in one year: approximately 5.88 trillion miles or 9.46 trillion km. For example, the north star Polaris is about 323 light-years away Earth. Whenever you see this star, you see light that is more than 300 years old.
So you don’t even need a fancy telescope to see into the past; You can do it with your own bare eyes. But to really see far into the past (e.g. back to the beginning of the universe), astronomers need telescopes like JWST. Not only can JWST zoom in on distant galaxies to observe visible light from many millions of light-years away, but it can also capture wavelengths of light invisible to the human eye, such as B. Infrared waves.
Many things, including people, emit heat as infrared energy. This energy cannot be seen with the naked eye. But when viewed with the right equipment, infrared waves can reveal some of the hardest-to-find objects in the universe. Because infrared radiation has a much longer wavelength than visible light, it can pass through dense, dusty regions of space without being scattered or absorbed NASA (opens in new tab). Many stars and galaxies that are too distant, faint, or obscured to be seen as visible light emit thermal energy that can be detected as infrared radiation.
This is one of JWST’s most handy tricks. Using its infrared-sensitive instruments, the telescope can peer past dusty regions of space to study light emitted by the universe’s oldest stars and galaxies more than 13 billion years ago.
This is how JWST captured its famous deep field image, and this is how it will try to look even further into the past, to the first few hundred million years (opens in new tab) after this Big Bang. The stars the telescope will reveal may actually be long dead today, but as their ancient light begins its long journey across the universe, JWST treats our mortal eyes to a unique time-travel display.
Originally published on Live Science.
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