Today is the 30th anniversary of the most influential telescope in history! Over the years, the Hubble Space Telescope has given us bucketloads of astronomical discoveries and countless images from up there in space. So, today’s the perfect day to learn all about what makes Hubble so special.
What is the Hubble Space Telescope?
First things first, a little bit about what Hubble is. In 1990, the Hubble Space Telescope was the very first telescope to be launched into space. It orbits the Earth, able to ‘see’ 5 times sharper than ground-based telescopes. It contains a 2.4m primary mirror, and 5 different science instruments, which allow it to observe across the entire optical spectrum. Hubble was able to see further and in more detail than any telescope before it, providing scientists with a whole new outlook on the universe.
A telescope in space was a huge step forward for observational astronomy for one very big reason: our atmosphere. When light from distant stars travels through space, the vacuum means that there isn’t anything getting in its way. The light can travel unimpeded towards us. Then, at the last minute, it suddenly has to contend with the millions of molecules in our atmosphere. Any images we take come out slightly blurry because the light bounces off the molecules and gets scattered all over the place. In other words, there is a limit to the detail we can see from the Earth. Therefore the logical solution is to observe from space!
Hubble is what’s known as a Cassegrain reflector telescope. Generally telescopes come in two different types: reflectors and refractors. Reflectors use mirrors to reflect and focus the light into the eyepiece, whereas refractors use lenses to refract or ‘bend’ the light towards the eyepiece. A Cassegrain reflector has two mirrors. A large, primary mirror reflects light towards a smaller, secondary mirror. This mirror then reflects the light back through a small hole in the primary mirror, where it is then ‘seen’ by the instruments.
The History of the Hubble Space Telescope
Any spacecraft that’s been operational as long as Hubble has is sure to have some stories to tell! This story is about how the Hubble Space Telescope became the most successful scientific instrument of all time. It had a particularly rocky beginning though!
Funding was first approved by the American congress in 1977, and from there it took 8 years to complete the construction. It was known as the Large Space Telescope, but in 1983 it was renamed after renowned astronomer Edwin Hubble. Then, in 1986, diaster struck at NASA. On it’s 10th launch, the Challenger space shuttle exploded 73 seconds after lift-off, killing all 7 of its crewmembers. NASA were forced to seriously reconsider future space missions, and shuttle launches were put on hold. The launch of the Hubble Space Telescope was postponed. But in 1990, a new shuttle called Discovery carried it into orbit.
On the 24th April, Hubble was launched into space, and the space shuttle crew deployed it into orbit the very next day. But almost immediately, another diaster became apparent. The first images to come back to Earth from the telescope revealed that the primary mirror had an imperfection known as ‘spherical aberration’. Mirrors and lenses in telescopes need to be made with incredible precision, and the bigger they are the more important it is. This miniscule error in construction meant that the images came back blurry – counteracting the reason for a space telescope in the first place!
Servicing Missions
Luckily, Hubble had something no space telescope has had since – astronauts trained and ready to service it! The First Servicing Mission was now far more important then planned. Scientists began working hard to build COSTAR – a device full of mirrors that would correct the aberration. In 1993, astronauts aboard the space shuttle Endeavour installed COSTAR, amoung other things, and Hubble could finally begin its exploration of the universe.
Between 1997 and 2009, there were four more servicing missions, allowing Hubble to continue making observations far longer than it would do alone. It’s now on borrowed time – there are no plans for further services or repairs, so once Hubble stops working, that’s it. Already, it has surpassed expectations on its lifespan, and it will soon be joined in orbit by the James Webb Space Telescope, due to launch in 2021.
What discoveries has it made?
The Hubble Space Telescope is the most successful scientific instrument in history. As of 2018, more than 15,500 scientific papers have been published using Hubble data. In its 30 years, Hubble has observed comet Shoemaker-Levy 9 collide with Jupiter, measured the elements in the atmospheres of exoplanets, discovered moons around Pluto, helped map the distribution of dark matter in the universe and more. But it is best known for the famous Hubble Deep Field (HDF).
The Hubble Deep Field
In 1995, scientists pointed Hubble towards a seemingly empty patch of sky. They were rewarded with an image rich in galaxies; Hubble’s superior, unobscured gaze revealed that the apparent nothingness was actually full of things we can’t see. These galaxies are really far away, hence their faintness. And this got scientists super excited; now they could see back in time and study the origin of the universe.
That last sentence might have confused you a little! Don’t worry, there’s a good reason. When we see something, it’s because light is bouncing off the object (or in the case of stars and galaxies, emitted from them) and travelling into our eyes. Telescopes work in the same way. But, like anything, light has a maximum speed, so takes time to reach anything. We don’t notice it in day-to-day life, as it travels so fast the time it takes to reach our eyes is miniscule. But when something is really far away, that light takes a noticeable amount of time to reach us.
Light from the Sun takes 8 minutes to reach us here on Earth. In contrast, the light from some of the galaxies in the HDF takes 13 billion years to reach us, meaning they appear in our observations as they were just half a billion years after the Big Bang. The results from the HDF were so important, that in 2004, a new image was created called the Hubble Ultra Deep Field, which used a newly installed camera to take the deepest image of the universe ever taken. And in 2012, the Hubble eXtreme Deep Field was published; a combination of over 2000 previous exposures.
Happy Birthday!
There’s no denying that the Hubble Space Telescope is a true marvel of humankind. Find out more about the birthday celebrations on the Hubble website, and you can join in a livestream with experts from around the world at 15:30 BST. Happy birthday, Hubble!
Sources: ESA/ Hubble, NASA Hubblesite, Space.com, James Webb Space Telescope