Webb vs Hubble

Comparison of the sizes of the mirrors of the Hubble Space Telescope, the James Webb Space Telescope, and the Spitzer Space Telescope. (Source : NASA-CSA)

Billed as the successor to the Hubble Space Telescope and the Spitzer Space Telescope, there are several key differences between Webb and Hubble, including:

The Webb telescope The Hubble telescope
Dimensions The Webb telescope will be the size of a tennis court (almost 22 metres long). Hubble's is about as long as a school bus (about 13.5 metres)
Mirror Webb mirror will be 6.5 metres. This means that Webb's collecting surface is seven times larger than Hubble's mirror. This means that Webb will collect much more light from faint objects, allowing it to look deeper into the universe than Hubble, and see farther back in time (because of the time it takes light to travel, the further away an object is, the further back in time we are looking). Essentially, if Hubble can see the equivalent of "toddler galaxies" in the early universe, the Webb Telescope will be able see "baby galaxies". Hubble's mirror is 2,4 metres
Infrared / Ultra-violet Infrared:
Webb will primarily look at the Universe in infrared light. Spitzer operates at the same wavelengths as Webb but is much smaller and has much less sharp images.
Hubble studies it at optical (visible light) and ultra-violet wavelengths.
Position Webb will be 1.5 million kilometres from our planet at a point in space known as Lagrange 2 - 2500 times farther away than Hubble. This also means that Webb will be too far from Earth to be repaired by astronauts, and will not be serviced in the same way Hubble was. However, Webb's location at Lagrange 2 means that it will be on the opposite side of Earth from the Sun. Along with Webb's enormous solar shield, this will block out light from the Sun, Earth and Moon, and allow Webb to stay cool (very important for an infrared telescope). Hubble orbits the Earth at an altitude of about 570 km.
Capacity In terms of its size and position in space, Webb will surpass other instruments (both on Earth and in space) by a factor of 10 to 100 000 depending on the type of observations carried out.