Today we will discuss about a recent exciting topic: the James Webb Space Telescope along with its predecessor Hubble Telescope. It will be four-part series, which will cover the various aspect of such telescopes stationed outside the Earth. Today we will start with a comparison of the two telescopes on technical and physical parameters.
NASA launched James Webb Space Telescope (JWST) on December 24. JWST will succeed the Hubble Space Telescope, NASA’s flagship telescope that has been in service for more than three decades. NASA says Webb is not Hubble’s replacement — rather, its successor whose science goals were motivated by the results from Hubble.
JWST four instruments to capture images and spectra of astronomical objects will provide wavelength coverage in the infrared part of the electromagnetic spectrum. Whereas, the instruments on Hubble can observe mainly in the ultraviolet and visible parts of the spectrum.
Infrared observations are important because light at this wavelength can penetrate the dust that shrouds newly formed stars and planets, and make them visible.
JWST’s primary mirror is approximately 6.5 meters in diameter, giving it a significantly larger collecting area than the mirrors of the current generation of space telescopes. Hubble’s mirror has a diameter of 2.4 meters, which means JWST’s collecting area is around 6.25 times that of Hubble’s. JWST will cover more than nearly 15 times the field of view covered by Hubble’s camera.
JWST’s sun shield is about 22 m by 12 m, a little less than the size of a tennis court.
Hubble orbits the Earth at an altitude of about 570 km. JWST will not orbit the Earth, instead, it will sit at the Earth-Sun L2 Lagrange point, 1.5 million km away. This means that JWST will orbit the Sun along with the Earth, but will stay fixed at the same spot in relation to the Earth and the Sun.
At the L2 point, Webb’s solar shield will block the light from the Sun, Earth, and Moon, which will help it stay cool — important for an infrared telescope.
Because light takes time to travel, the farther away an object is, the farther back in time we are looking. Thus, while Hubble can see the equivalent of “toddler galaxies”, JWST will be able to see “baby galaxies”. This is also because JWST is an infrared telescope, and can see distant objects which are very dim at visible wavelengths of light.