Space Explorations – James Webb telescope

By LIONEL PALLIYAGURU

I have been a sky gazer for more than four decades, a habit which started in my school days. As an amateur astronomer, stargazing usually starts from the backyard, with or without any supporting instruments like binoculars or telescopes. Identifications of whatever celestial objects become the first task, with the help of elders who are relaxing in the backyard invariably after supper.

As one develops a keen interest in astronomy, reading and studying astronomy with advanced telescopes become a reality. I have passed many stages in life, and enjoy my retirement life devoting ample time to my hobbies of which astronomy becomes my favourite subject.

It is well known that the James Webb Space Telescope (JWST or WEBB) is in operation with full potential, and incredible photos sent by JWST of distant galaxies could be seen on the NASA website as well as on public media.In order to explore the universe, various projects have been launched by many countries, of which NASA and the European space agency have contributed, by placing complex telescopes operational in outer space.

It is well known that the JWST is the most advanced telescope in operation since July 2022. It is equipped with the most sophisticated instruments with state-of-the-art technologies, and surpasses the capabilities of the Hubble Space Telescope (HST or HUBBLE), which was launched in 1990.

JWST was launched in December 2021 on an Ariane 5 rocket and travelled 1.6 million kilometres in space, to reach its final orbit around the sun, which takes one year to complete one revolution. Whereas its predecessor, HST was launched using Space Shuttle Discovery and placed in a geocentric orbit around the Earth with, an altitude of 547 kilometres at an elevation angle of 28 degrees with the equator. HST takes about 95 minutes to go around the earth and completes 15 orbits per day.

HST is equipped with instruments to probe the composition of the atmosphere of our solar system and extrasolar planets, normally referred to as exoplanets. HUBBLE can capture ultraviolet, visible, and near-infrared wavelengths of light. Although near-infrared radiation is detectable by the human eye, mid and far-infrared regions are less susceptible to the human eye. As the Hubble Space Telescope operates above 547 kilometres above Earth, Hubble can capture visible and infrared spectra with minimum interference.

In order to obtain a high degree of accuracy, space observations should be carried out outside the earth’s atmosphere, where obstruction to visible light and infrared light is minimal. Mathematician Joseph Louis Lagrange has discovered five locations with respect to the sun and earth, where observatories could be parked for various astronomical activities. They are known as Lagrange points and are denoted as L1, L2, L3, L4 and L5. in honour of him.

In these special locations, gravitational and rotational forces cancel each other out, creating ample parking space for telescopes and observatories. Any small mass object placed at the Lagrange point, moves in sync with the Earth, although they are in two different orbits around the sun.

The L2 point is advantageous in many ways for astronomy. The JWST can communicate continuously with Earth while providing a clear view into deep space. Interference from Sun and Earth could be kept to a minimum, as Sun and Earth are behind the telescope. Sun, Earth and L2 points are on a straight line keeping L2 at 151.5 million kilometres away from the Sun and 1.5 million kilometres away from the Earth. To stay in this position minimum station-keeping manoeuvres have to be performed occasionally, which reduces the propellant requirement considerably. As a result, the lifetime of the JWST is increased proportionately.

It took about twenty years to develop the most powerful telescope, costing 10 billion US dollars, in collaboration with the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA), and the Canadian Space Agency (CSA). In addition to the main collaborators, there were about 15 other countries involved and contributed in many ways to making this mission a reality. This astronomical telescope was named as James Webb Space Telescope in honour of James Edwin Webb, who served NASA as an administrator during many critical space missions.

JWST design exceeds all the capabilities of its predecessor, and is expected to uncover the mysteries of the universe, by observing events that have taken place at a distance of 13.6 billion light-years away from Earth. In astronomy, distance is measured in light years. Light-year is the distance that light travels in a year at a speed of 300,000 kilometres per second, which is equivalent to 9.46 trillion kilometres.

Telescopes can go back in time. Looking out in space is looking back in time. Light takes time to travel vast distances in space to reach us. The light from the moon, which is about 390,000 kilometres away from us, takes 1.3 seconds to reach us meaning that we see the moon 1.3 seconds ago. Similarly, light takes about eight minutes to travel from the Sun, which is about 150 million kilometres away from the Earth. Inferring from that, what we see is the Sun about eight minutes ago. When the distances are in the order of billions, light takes years to reach the earth.

JWST is equipped with a) Mid-Infrared Instrument (MIRI), b) Near-Infrared Camera (NIRCam), c) Near-Infrared Spectrograph (NIRSpec), d) Fine Guidance Sensor (FGS), e) Near-Infrared Imager and Slitless Spectrograph(NIRISS). These equipment facilitate measurements of Redshift and Spectroscopy of various objects in the universe such as stars, galaxies, etc. As these instruments monitor the infrared region of the electromagnetic spectrum, all equipment has to be cryogenically cooled to avoid interference within equipment and from outside. The operating temperature is set to minus 266 degrees celsius, which is closer to absolute zero. Absolute zero is minus 273.15 degrees celsius, and the lowest possible temperature to reach. Extremely low operating temperature indicates the unprecedented sensitivity of its infrared equipment.

NASA claims that the sensitivity of infrared equipment onboard the WEBB could detect the heat of a bumblebee at a distance from the moon. Further, details of a small coin of one-centimetre size could be seen at a distance of 40 kilometres away.

In astronomy, redshift has been classified into three categories namely; a) Gravitational, b)Doppler, and c) Cosmological. Redshift is a phenomenon applicable to light sources moving away from an observer. In general, redshift is defined as an apparent increase in the wavelength (or decrease in frequency) of light waves, received from a moving source away from an observer. This is due to the stretching of the wavelength towards the red boundary of the spectrum.

Conversely, when the moving source of light is approaching the observer, a decrease in the wavelength (or increase in frequency) occurs. This is due to apparent compression of wavelength towards the blue boundary of the spectrum known as Blueshift.

Also, when a star rotates, one edge of the star is moving towards us relative to its centre, while the other edge is moving away. As a result, light from one edge of a star is slightly red-shifted, while light from the other edge is slightly blue-shifted. Astronomers can use these two shifts in order to calculate how fast a star is rotating. The same approach can be used to calculate how fast a galaxy is rotating. By evaluating the Redshift, the distance and velocity of any space object could be calculated. Conversely, Blueshift provides parameters of distance and velocity of an approaching object.

Astronomical spectroscopy is mainly concerned with the analysis of objects such as stars, planets, nebulas, and galaxies in space. It is done by splitting the received infrared spectrum into its various wavelength components. The spectrum patterns of a star can be compared with known spectrum patterns of hydrogen, oxygen, carbon and other elements to determine the physical and chemical composition of the star.

The media has shown magnificent and colourful photos of various stars, galaxies and nebulas released by NASA. Anybody would wonder about the process of producing such stunning photos from faraway galaxies many light years away from the Earth. These images are captured using infrared cameras and the spectrum is split into many different frequency bands using filters. Different colours are assigned to each frequency band during processing to obtain spectacular photos. A similar process is being used in digital colour cameras in processing visible light photos.

James Webb Space Telescope is expected to function at full capacity for a minimum of 10 year period. Scientists and Astronomers work tirelessly to explore discoveries of our universe, and life beyond our Earth, which is one of the key objectives of this mission.

This writer could be contacted on – lionelpg@gmail.com