What is the James Webb Telescope?
The James Webb Space Telescope (JWST) is a space telescope primarily designed for infrared astronomy. As the largest optical telescope in space, its high infrared resolution and sensitivity allow it to see objects that the Hubble Space Telescope cannot see because they are too early, distant, or faint. This is expected to enable a wide range of astronomical and cosmological investigations, such as the observation of the first stars and the formation of the first galaxies, as well as detailed atmospheric characterization of potentially habitable exoplanets.
James Webb Telescope Power
Astronomers at NASA, the European Space Agency, and the Canadian Space Agency recently released an unprecedented view of the Tarantula Nebula, a massive region of swirling gas and dust. This nebula, which is 161,000 light-years away (relatively close in cosmic terms), is also "home to the hottest, most massive stars known." The James Webb Space Telescope, which captures unprecedented amounts of light from deep space and views wavelengths that our eyes cannot see (infrared light), revealed thousands of massive, previously unseen stars in that central cluster.
James Webb Telescope Mission
The James Webb Space Telescope has four primary objectives:
To look for light from the universe's first stars and galaxies after the Big Bang
To investigate the formation and evolution of galaxies
To comprehend the formation of stars and planets
To investigate the origins of life and planetary systems
These objectives can be accomplished more effectively by observing in near-infrared light rather than visible light. As a result, unlike the Hubble Telescope, the JWST's instruments will not measure visible or ultraviolet light, but will have a much greater capacity for infrared astronomy. JWST will be sensitive to wavelengths ranging from 0.6 to 28 m (corresponding to orange light and deep infrared radiation at around 100 K or 173 °C).
JWST could be used to gather data on the dimming light of KIC 8462852, a star discovered in 2015 with some unusual light-curve properties. It will also be able to detect methane in an exoplanet's atmosphere, allowing astronomers to determine whether or not the methane is a biosignature.
Telescope Structure
The James Webb Space Telescope is the biggest space telescope ever constructed. It is nearly double the size of the Hubble Telescope (13m long) and roughly half the Hubble’s weight (6,500kg). Its humongous sun shield stand measures 22m by 12m, almost the same dimension as a tennis court.
James Telescope’s gold-coated mirrors have a cumulative diametre of 605cm, more than twice the diameter of Hubble (240cm). In short, JWST will roughly have a fifteen times broader view than the Hubble Space Telescope.
The optical telescope components of the primary mirror have eighteen six-sided mirror segments, which are made of gold-coated beryllium. This grants the JWST a light-gathering area about 5.5 times as big as Hubble’s area.
Hubble captures images from the range of visible, ultraviolet and near-infrared spectra. On the other hand, the James Webb Space Telescope will detect objects in the range of long-wavelength normal red light and mid-infrared spectrum. This will allow the detection of high-redshift celestial bodies that are too faint, distant, and old.
The ideal working temperature of the Webb telescope is below -223 °C. By maintaining such a low temperature, it will be able to detect faint signals in the infrared spectrum without the intrusion of warmer signals of objects.
It is orbiting near the Sun-Earth L2 Lagrange area, around 1.5 million kilometres away from the Earth. A five-layered windshield guards it against the Sun’s direct heat waves.
James Webb Space Telescope
Important Questions
1. How does the James Webb Space Telescope expand our understanding of galaxies?
Ans: Galaxies show us how matter is organised on a large scale in the universe. Understanding galaxies is critical if we are to comprehend the origins of the universe and its evolution over time. By analysing some of the earliest galaxies and comparing them to modern galaxies, we may be able to understand the development and evolution of galaxies. Observations from events that occurred during the universe's formation will allow scientists to solve unsolved mysteries.
2. Briefly describe the technology used in JWST.
Ans: The JWST is envisioned as an integrated telescope that incorporates features from predecessors, such as the Hubble and Spitzer telescopes. JWST's major technological innovations include:
Cryogenic mirrors that are lightweight
The process of aligning the JWST mirror segments is known as wavefront sensing and control.
Infrared detectors that are extremely sensitive.
Integrated Circuit for Cryogenic Data Acquisition.
To see faint infrared emissions from astronomical objects, the JWST telescope and instruments must be cooled below 50 degrees Celsius. This is done by the sunshield.
Microshutters
Solved Examples
1. In an astronomical telescope, the focal length of the objective lens is 100cm and the focal length of the eyepiece lens is 8cm. What is the magnifying power of the telescope?
Ans:
The magnifying power of the telescope is given by:
M= -focal length of the objective lens/focal length of eyepiece lens
M= -100cm/8cm
M= -12.5
Here, the minus sign indicates that the image is inverted.
2. A simple telescope consists of two convex lenses, the objective and the eyepiece, which have a common focal point P, as shown in the figure above. If the focal length of the objective is 1.0 metre and the angular magnification of the telescope is 10, what is the optical path length between objective and eyepiece?
Ans:
Magnification(M)= focal length of the objective/focal length of the eyepiece
Since M=10, focal length of the objective= 1
Focal length of eyepiece= focal length of objective/Magnification= 1/10 = 0.1
d= focal length of objective+focal length of eyepiece = 1+0.1 = 1.1 m
Conclusion
The JWST is the most advanced telescope in existence. It will use cutting-edge technology to offer profound insights into a vast, undiscovered universe. The observations by this telescope are likely to expand our understanding of galaxies and the formation of planets including earth. The James Webb Space Telescope (JWST) is a space telescope designed primarily to conduct infrared astronomy. As the largest optical telescope in space, its high infrared resolution and sensitivity allow it to view objects too early, distant, or faint for the Hubble Space Telescope.
FAQs on James Webb Space Telescope
1. What is the primary purpose of the James Webb Space Telescope (JWST)?
The James Webb Space Telescope is designed to conduct advanced infrared astronomy to uncover the history of the universe. Its four main scientific objectives are:
- To search for the first light from stars and galaxies that formed just after the Big Bang.
- To study the formation and evolution of galaxies over cosmic time.
- To understand the birth of stars and the formation of planetary systems.
- To investigate planetary systems and the origins of life by studying the atmospheres of exoplanets.
2. How is the James Webb Space Telescope different from the Hubble Space Telescope?
The JWST differs significantly from the Hubble Telescope in its capabilities and design, making it a successor, not a replacement. Key differences include:
- Wavelength: JWST is optimised for the infrared spectrum, allowing it to see through cosmic dust and observe highly redshifted early galaxies. Hubble primarily observes in the ultraviolet and visible light spectra.
- Size: JWST's primary mirror is 6.5 metres in diameter, giving it a much larger light-collecting area than Hubble's 2.4-metre mirror. Its sunshield is the size of a tennis court.
- Orbit: JWST orbits the Sun at the second Lagrange point (L2), 1.5 million km from Earth. Hubble orbits the Earth at an altitude of about 570 km.
- Observation Range: Due to its infrared sensitivity, JWST can observe the universe's 'infancy,' capturing light from the very first stars and galaxies, which are too distant and old for Hubble to see.
3. Where is the James Webb Telescope located and why was that location chosen?
The James Webb Space Telescope is located at the second Lagrange point (L2), which is approximately 1.5 million kilometres away from Earth in the direction opposite the Sun. This specific location was chosen because it allows the telescope's massive sunshield to block heat and light from the Sun, Earth, and Moon simultaneously, keeping the telescope's sensitive instruments at the extremely cold temperatures required for detecting faint infrared signals.
4. Which international space agencies collaborated to build the James Webb Space Telescope?
The James Webb Space Telescope is the result of a major international partnership. The lead agency is NASA (National Aeronautics and Space Administration) of the United States. Its primary partners are the European Space Agency (ESA) and the Canadian Space Agency (CSA), who contributed key instruments and operational support.
5. Why is observing in the infrared spectrum so important for achieving the JWST's goals?
Observing in infrared light is critical for several reasons. Firstly, as the universe expands, light from the earliest stars and galaxies is stretched to longer wavelengths, a phenomenon known as redshift. This shifts their light into the infrared range. Secondly, infrared radiation can penetrate the dense clouds of cosmic gas and dust where new stars and planetary systems form, allowing us to see processes that are hidden in visible light. Lastly, cooler objects like exoplanets and brown dwarfs emit most of their energy as infrared radiation.
6. What makes the gold-coated beryllium mirrors of the JWST so special for its mission?
The mirrors are an engineering marvel designed for extreme conditions. Beryllium was chosen because it is both lightweight and strong, and it maintains its shape at the cryogenic temperatures required for the telescope. A microscopic layer of gold is used to coat the mirrors because it is highly effective at reflecting infrared light, which is crucial for capturing faint signals from the distant universe. This combination ensures maximum sensitivity and image clarity for its scientific instruments.
7. How does the JWST's multi-layered sunshield protect its sensitive instruments?
The JWST's sunshield consists of five layers of a special material called Kapton, each as thin as a human hair. It works by separating and radiating heat into space. The vacuum between each layer acts as an excellent insulator. The first layer blocks most of the Sun's heat, and the residual heat is radiated out from between the layers. This design brings the temperature from a sun-facing high of about 85°C down to a frigid -233°C on the side where the telescope's optics and instruments are located.
