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©2018 Reaching Space Science. 

Hubble Vs. James Webb: Differentiating the two most Famous Space Telescopes

July 2, 2018

Although many telescopes exist around the world to look deep into space, there are also special space telescopes that explore our cosmos from beyond the Earth's atmosphere. 


Telescopes collect light from far away and deliver it to a detector. Some use lenses to concentrate and focus the light, while others make use of mirrors. One of the most famous and successful of such spacecraft is the Hubble Space Telescope, which has delivered inspiring photographs and knowledge of our cosmos. Launched in 1990, this project remains in operation today and is comparable to the size of a school bus. Its observations have helped us better estimate the age of the universe, once thought to between 10 and 20 billion years, to around 13.8 billion years. The universe’s age is also related to the rate of how quickly the universe is expanding, which was also determined by the telescope’s observations. In fact, the telescope found that this rate is accelerating. Images have helped prove the existence of black holes in the centres of large galaxies (including our own Milky Way), the detection of four new moons orbiting Pluto, the detection of planets in other star systems, and has visualized galaxies in the early universe. The Hubble Space Telescope has taken most of the clearest and awe-inspiring photographs of space.


This 2014 image from the Hubble Space Telescope is called the Ultra Deep Field.  Each of the bright blobs in this image is an entire galaxy, roughly 10,000 of them that each contain millions or billions of stars.


Hubble will soon be joined another telescope, the James Webb Space Telescope (JWST). This space-based observatory is (currently) scheduled for launch in 2021 and is a joint collaboration between the American, European and Canadian space agencies. Compared to Hubble, JWST will make more precise observations and will look further back in time to observe things that have never-before been captured. JWST will detect infrared light over four hundred times fainter than currently possible and will offer valuable insights into the early formations of our universe. To do this, the telescope will mainly be observing the cosmos in the infrared portion of the electromagnetic spectrum with a large telescope of 6.8 metres in diameter (roughly as tall as a giraffe). This is the biggest telescope mirror to ever operate in space, with an area six times greater than that of Hubble. Eighteen hexagon-shaped pieces made of gold-plated beryllium form the mirror, which is helped by a second mirror that reflects the light captured from the larger mirror to the different science instruments.


Although it can make some observations in infrared, the Hubble Space Telescope mainly studies the universe in the optical and ultraviolet wavelengths. Because it will observe longer wavelengths than Hubble, the JWST hopes to observe the first galaxies that formed in the early universe. This means that the telescope will observe how the universe appeared a quarter of a billion years, possibly back to 100 million years, after the Big Bang. Infrared observations can also see through dust clouds where new planets and stars are forming today. To see the first galaxies that formed after the Big Bang, we must observe the universe back in time because of the time it takes for light to travel to us. Because our universe is expanding, the further we look back in time, the faster objects will be moving away from us. This causes the light that the telescope captures to be “redshifted”. This means that the light that is shining from the early universe in ultraviolet or even visible light is "shifted" to wavelengths that are increasingly red. To account for this, the JWST is equipped with instruments that are designed for infrared light.


In order to see this form of light from distant stars and galaxies, the JWST must be kept cold, so a large sunshield will protect the telescope from both sunlight and radiation coming from Earth. The shield will cover the size of a tennis court and provide the equivalent of over one million SPF protection against the Sun’s rays. This will keep the observatory to a cold -225 degrees Celsius. For this protective sunshield to work, the JWST will need to be an orbit where the sun and Earth are approximately in the same direction.


Instead of orbiting around the Earth like Hubble, the JWST will actually be orbiting around an empty point in space that is located beyond the orbit of the moon. Hubble is positioned in an orbit around the Earth at a height of around 570 kilometres but the JWST will be roughly 1.5 million kilometres away from us. This special point is located in just the right spot to allow the gravitational forces of the Sun, Earth and the telescope to keep the JWST in its orbit. This “Lagrange” point was chosen because it is far enough away from Earth to keep the telescope at its needed cold operating temperature and so that it can see into deep space without being obstructed by our atmosphere. This point is also useful because to us, it will always appear in the same place in the sky. This means communications to and from the JWST will be easy for us. It will take the JWST around one month to get to this location on board the ESA's Ariane 5 rocket. Hubble was delivered to Earth's orbit by NASA's Space Shuttle and it could be fixed and serviced from space (which it was several times). Although the JWST is not planned to be serviced, it has been equipped with a docking ring in case servicing is someday needed (and if humans ever reach this far in to space - which so far they haven't).


The JWST project has unfortunately seen several delays and added expenses since its conception. The most recent delayed launch date is set for March 2021 and the total mission cost, including operations, may near close to $10 billion USD.





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