The James Webb Space Telescope (JWST) and Hubble Space Telescope are complementary observatories rather than direct replacements, differing primarily in their wavelength focus and locations. Hubble operates mainly in visible and ultraviolet light, while Webb is optimized for infrared light, allowing it to peer through cosmic dust and see the earliest, most distant galaxies.

Why Hubble is still vital:

• Ultraviolet Vision: Hubble can detect ultraviolet light, which is crucial for studying the atmospheres of planets and the hottest, youngest stars. Because Earth's atmosphere blocks UV light, a space-based telescope is required to see it.
• Visible Light: It sees in the same wavelengths as the human eye, providing the iconic, crisp, true-color images of the cosmos we are most familiar with.

Why James Webb is more advanced:

• Infrared Capabilities: Because the universe is expanding, light from the most distant objects gets stretched (redshifted) from visible light into the infrared spectrum. Webb's infrared instruments are designed to detect these ancient, faint light sources.
• Dust Penetration: Infrared light can pass through thick clouds of cosmic gas and dust. This enables Webb to look inside stellar nurseries and see infant stars that are completely hidden from Hubble's view.
• Larger Light-Gathering Area: Webb's gold-coated honeycomb mirror is much larger than Hubble's, giving it roughly six times the light-collecting power. This allows Webb to see objects up to 100 times fainter than Hubble.

Location and Maintenance: Hubble orbits just above Earth's atmosphere, allowing astronauts to physically visit and service the telescope (which they have done several times since its 1990 launch). Webb, on the other hand, is positioned a million miles away at the second Lagrange point (L2). This deep-space orbit keeps the telescope cool and shields it from the heat and light radiating from Earth, which is essential for its sensitive infrared instruments.

For a side-by-side visual comparison of images taken by both Hubble and Webb, showing exactly how much deeper JWST can see:

See also this comparative image and also this comparative image

NASA Site = https://science.nasa.gov/mission/hubble/observatory/hubble-vs-webb/

The Hubble Space Telescope
Launched in 1990, the NASA/ESA Hubble Space Telescope orbits 332 miles above Earth. By peering above the atmospheric distortion, this bus-sized observatory delivers ultra-sharp optical, ultraviolet, and near-infrared images that have revolutionized humanity's understanding of the universe, including the discovery of dark energy.

Quick Facts

• Launch: April 24, 1990 (via Space Shuttle Discovery)
• Orbit: Low-Earth orbit at ~569 km (~332 miles)
• Size: 13.2 meters (43 feet) long with a 2.4-meter (94-inch) primary mirror
• Wavelengths: Ultraviolet, visible, and near-infrared

Scientific Legacy
Hubble has performed over 1.7 million observations and has been central to some of the most significant astronomical breakthroughs of the modern era:

• Dark Energy: Discovered in 1998 that the expansion of the universe is accelerating.
• Exoplanet Atmospheres: Pioneered the field of studying the atmospheric composition of planets beyond our solar system.
• Deep Fields: Created breathtaking "deep field" images—like the Hubble Ultra Deep Field—revealing thousands of previously unseen, distant galaxies.
• Age of the Universe: Helped determine the expansion rate of the universe and pinpointed its age to approximately 13.8 billion years.

How It Works
Unlike ground-based telescopes, which must peer through the shifting, hazy layers of Earth’s atmosphere, Hubble has a direct window to the cosmos. Starlight enters the telescope and hits the primary mirror, which reflects the light onto specialized instruments. These include cameras to capture its iconic imagery and spectrographs used to analyze the chemical composition of stars, planets, and galaxies.

Maintenance and Future
Unlike most space probes, Hubble was specifically designed to be serviced by astronauts. Between 1993 and 2009, space shuttle crews completed five complex repair and upgrade missions. Today, while it is nearing the end of its operational lifecycle and grappling with aging gyroscopes, it continues to operate in tandem with the James Webb Space Telescope to map the cosmos.

NASA Site = https://science.nasa.gov/mission/hubble/

The James Webb Space Telescope
The James Webb Space Telescope (JWST) is NASA's most powerful space observatory. Designed to succeed the Hubble Space Telescope, its primary mission is to look back 13.5 billion years to observe the first galaxies born after the Big Bang and to study the atmospheres of distant alien worlds.

How It Works

• Infrared Vision: Unlike Hubble, which primarily sees visible light, Webb focuses on infrared astronomy. Because the universe is expanding, light from the earliest stars and galaxies stretches into the red and infrared spectrum—a phenomenon called redshift.
• Gold-Plated Mirrors: Its iconic 21.3-foot primary mirror is composed of 18 hexagonal segments made of beryllium and coated in a microscopically thin layer of pure gold to optimize the reflection of infrared light.
• Tennis-Court Sunshield: Because the telescope operates via heat-sensitive infrared detectors, it utilizes a five-layer, tennis-court-sized sunshield that blocks the heat and light of the Sun, Earth, and Moon.

Where It Lives
Webb does not orbit Earth. It is parked in a "halo orbit" around the second Lagrange point (L2), which is located about 1 million miles (1.5 million kilometers) away from Earth. This position keeps the Earth and Sun in a straight line behind the telescope's sunshield, allowing it to stay extremely cold and undisturbed.

Key Scientific Goals

• The Early Universe: It acts as a time machine to study the "Cosmic Dawn," observing how the very first galaxies and stars formed and evolved.
• Exoplanet Atmospheres: By analyzing starlight passing through the atmospheres of planets outside our solar system, Webb can detect chemical fingerprints—such as water vapor, methane, and carbon dioxide—assessing if an exoplanet might be habitable.
• Star Lifecycles: Webb's infrared instruments can peer directly through thick, opaque clouds of cosmic dust where baby stars and planetary systems are actively being born.

NASA Site = https://science.nasa.gov/mission/webb/