Earlier this year, the new Vera C. Rubin Observatory in Chile officially began scientific operations, becoming the world’s largest and most advanced ground-based telescope. Featuring an eight-meter primary mirror and the world’s largest camera, Rubin promises to deliver exceptional new results and astrophysical research opportunities for scientists worldwide.
Meanwhile, situated at the L2 Lagrange point is the world’s newest and most advanced space telescope — the James Webb Space Telescope. Since becoming operational in July 2022, Webb has revolutionized astronomy with its unprecedented views of the universe and its ability to see back in time using its impressive suite of infrared instruments.
Both telescopes represent different technological solutions to mapping and analyzing the cosmos, and together they are poised to reveal untold information about our universe. However, besides the differences in their locations (ground-based versus space-based), how similar are these two physics and engineering masterpieces?
A drone view of NSF–DOE Vera C. Rubin Observatory during the First Look observing campaign. (Credit: Rubin Observatory/National Science Foundation)
The Vera C. Rubin Observatory
The Rubin Observatory operates from Cerro Pachón in Chile’s Atacama Desert, capitalizing on the optimal atmospheric conditions for ground-based observations. Optimal observing conditions include minimal cloud cover, dry atmospheric conditions, and negligible light pollution, enabling the detection of faint celestial objects with reduced optical distortion. The facility conducts the Legacy Survey of Space and Time (LSST), photographing the entire visible southern sky every few nights over a planned decade-long survey period.
For observations, Rubin employs an 8.4 m primary mirror featuring an integrated primary/tertiary surface design. This monolithic structure, combined with a three-mirror optical system, enables a 3.5-degree field of view. Rubin’s 3.5-degree field captures approximately 49 times more sky area than the Earth’s Moon.
Furthermore, Rubin’s 3.2-gigapixel camera comprises 201 individual charged-coupled devices (CCDs) arranged in a mosaic configuration. Nightly operations generate approximately 20 terabytes of data, processed through automated systems that compare new observations against previous datasets.
Real-time processing capabilities can generate up to 10 million alerts per night when changes to existing objects or the introduction of new objects are detected. The “10 million alerts” figure represents the scale of astronomical activity constantly occurring across the southern sky — most are routine variable star fluctuations, but hidden among them are rare, exotic events that potentially represent entirely new classes of astronomical phenomena. The Rubin Science Platform (RSP) provides cloud-based data access, eliminating the need for researchers to download massive datasets locally.
The James Webb Space Telescope
The James Webb Space Telescope (JWST) operates from a halo orbit around the Sun-Earth L2 Lagrange point, positioned approximately 1.5 million km from Earth. L2 represents a gravitationally unstable equilibrium point, requiring JWST to execute periodic station-keeping maneuvers with onboard thrusters to prevent orbital drift. The telescope traces a complex, elliptical trajectory that oscillates around L2, alternating between positions above and below the ecliptic plane while matching Earth’s orbital period due to the combined effects of the Sun and Earth’s gravitational forces.
The L2 location also offers significant thermal advantages by maintaining distance from Earth and lunar heat sources, with JWST’s sunshield blocking solar thermal interference. The telescope often experiences temperature differentials of up to 600 degrees Fahrenheit across its structure while operating its cryogenic instruments at just a few degrees (Kelvin) above absolute zero.
James Webb’s sunshield fully deployed before launch in December 2021. (Credit: NASA/Chris Gunn)
This orbital configuration enables consistent Earth communication throughout most operational periods while preserving unobstructed views of deep space targets. After arriving at L2, the telescope underwent a complex unfolding maneuver to prepare for operations. JWST’s deployment sequence involved critical steps such as the unfurling of the sunshield and the exact positioning of the mirror segments.
JWST’s 6.5-meter segmented primary mirror consists of 18 hexagonal beryllium segments with gold coating. Each segment utilizes 132 actuators for nanometer-precision positioning, enabling optimal optical alignment in space. The light reflected by this mirror is channeled to four specialized instruments: the Near-Infrared Camera (NIRCam), the Near-Infrared Spectrograph (NIRSpec), the Mid-Infrared Instrument (MIRI), and the Fine Guidance Sensor and Near-Infrared Imager and Slitless Spectrograph (FGS/NIRISS).
These systems employ mercury-cadmium-telluride and arsenic-doped silicon detectors operating near absolute zero temperatures. Thermal management of Webb’s systems relies on a five-layer sunshield spanning dimensions similar to a tennis court, and supplemented by active cryocoolers. Daily science data production averages 57 gigabytes, transmitted to Earth via Ka-band communications. The 68-gigabyte onboard storage capacity requires daily downloads to free up space for the next day’s observations, with data processing handled through the Mikulski Archive for Space Telescopes.
Rubin vs. JWST
While both telescopes vary significantly in their locations, size, and capabilities, they are still being used daily to make astrophysical observations that scientists will regularly utilize for decades to come. How do the two observatories handle their data, and how will scientists use them in the years to come?
The Rubin Observatory’s survey approach generates approximately 7.3 petabytes of data annually—exceeding the combined data from all previous optical telescopes. The automated survey methodology represents a shift toward “big data” astronomy, necessitating new analysis techniques for the unprecedented volumes of information.
JWST, on the other hand, produces roughly 350 times less data than Rubin, but focuses on precision observations that require hours of integration time per target rather than spanning surveys. Each observation undergoes careful planning and multi-stage calibration processing before release to the scientific community.
This image shows a small section of the Rubin Observatory’s view of the Virgo Cluster, offering a vivid glimpse of the power of the observatory. (Credit: NSF–DOE Vera C. Rubin Observatory)
Thus, the facilities operate in complementary roles in modern astronomical research. Rubin functions as a wide-field reconnaissance system, systematically cataloging approximately 20 billion galaxies, 17 billion stars, and millions of asteroids across the southern sky. Meanwhile, JWST can provide observations of specific objects and phenomena in extreme detail, with the telescope’s infrared capabilities penetrating cosmic dust obscuration, enabling studies of early universe objects and regions of stellar formation
For example, when Rubin’s automated systems identify significant astronomical events such as supernovae, galaxy clusters, or potentially hazardous asteroids, JWST can provide detailed follow-up observations. Rubin’s time-domain astronomy capabilities track changes across the observable universe over the decade-long survey period. JWST’s instruments analyze the physical processes driving these temporal variations, creating a comprehensive understanding of cosmic evolution.
The telescopes also differ in their movement capabilities. Rubin’s engineering teams developed rapid slewing capabilities, achieving target-to-target movement in five seconds while maintaining optical stability for sharp imaging. JWST, though, can take upwards of an hour to perform a 90-degree slew.
A new image of the Ring Nebula from Webb’s MIRI instrument. (Credit: ESA/Webb, NASA, CSA, M. Barlow)
Both facilities address fundamental cosmological questions through different methodological approaches. The Rubin Observatory’s statistical surveys will constrain the properties of dark matter and dark energy while mapping large-scale cosmic structure. JWST’s detailed observations reveal the physics underlying cosmic phenomena at small scales. The combined capabilities enable comprehensive analysis spanning from early universe galaxy formation to potentially habitable exoplanet atmospheres.
Together, these observatories represent a powerful partnership in modern astronomy: Rubin’s wide-field surveys will systematically identify millions of transient events and catalog billions of cosmic objects. At the same time, JWST’s precision infrared capabilities will continue to provide detailed follow-up observations of the most scientifically significant targets.
(Lead image: (left) The Vera C. Rubin Observatory in Chile. Credit: NSF-DOE Vera C. Rubin Observatory. (right) Artist’s impression of the James Webb Space Telescope at L2. Credit: NASA GSFC/CIL/Adriana Manrique Gutierrez)
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