The James Webb Space Telescope: An Overview

The recently launched James Webb Space Telescope is the most advanced telescope we have built. In this article, I describe the telescope and its features.

Design and Instruments

The James Webb Space Telescope is divided into three parts: (1) the Integrated Science Instrument Module (ISIM), (2) the Optical Telescope Element (OTE), including the mirrors, backplane, and (3) the Spacecraft Element. The spacecraft element includes the Spacecraft Bus and Sunshield.

The primary goal of the Webb telescope is to make scientific measurements. The Integrated Science Instrument Module (ISIM) houses the instruments used for these measurements, a guide camera, a framework that provides electrical power, computing resources, cooling capability, and structural stability to the Webb telescope. 

NIRCam (Near InfraRed Camera) is an infrared imager that has a spectral coverage from visible light (0.6 μm) to near-infrared (5 μm). NIRSpec (Near InfraRed Spectrograph) will also perform spectroscopy over the same wavelength range. MIRI (Mid-InfraRed Instrument) will measure the mid-to-long-infrared wavelength ranging from 5 to 27 μm. It contains both a mid-infrared camera and an imaging spectrometer.FGS/NIRISS (Fine Guidance Sensor and Near-Infrared Imager and Slitless Spectrograph), is used to stabilize the line-of-sight of the observatory during science observations. The Near-Infrared Imager and Slitless Spectrograph (NIRISS) module is used for astronomical imaging and spectroscopy in the 0.8 to 5 μm wavelength range.

The OTE is the eye of the Observatory and it gathers the light coming from space and provides it to the science instruments located in the ISIM.

The James Webb Space Telescope has a 6.5-meter gold-coated beryllium primary mirror made up of 18 separate hexagonal mirrors. The gold coating helps reflect infrared wavelengths. The mirror by itself covers an area of 25.4 m2 (273 sq ft).

Webb’s sunshield keeps the heat of the Sun, Earth, and spacecraft bus electronics away from the scientific instruments which have to be maintained at a low temperature for proper operation.

Electromagnetic spectrum

Infrared wavelengths are a part of the electromagnetic spectrum covering the range from approximately 0.7 µm to 100 µm – more than 100 times as wide as the visible portion! 

Imaging in the infrared is useful because objects obscured by dust are visible in the infrared. Distant objects moving away from us at high speeds exhibit significant redshift which can be measured in the infrared portion of the spectrum.

The James Webb Space Telescope has infrared instruments to help study the origins of the universe and the formation of galaxies, stars, planets, etc. Its infrared resolution and sensitivity will allow it to view objects that are old, distant, or faint. The information from the telescope will help observe the formation of the first galaxies and stars, and detailed atmospheric characterization of potentially habitable exoplanets.

Webb can also observe nearby objects, including objects in the Solar System. This includes all planets and satellites, comets, and asteroids beyond Earth’s orbit, and known Kuiper Belt Objects. 


JWST was launched in December 2021 after nearly 20 years of design and development. It reached its final orbit and became operational in June 2022. In this article I have focused on the technical details of the telescope, its instruments.

The initial images that we have obtained since June have exceeded all expectations and have resulted in challenges to existing theories and potentially new science. Scientists have already started designing the next generation of telescopes which will likely be launched in future decades. A world of discovery lies ahead of us!