The Lens Dilemma in Family Portraits
When taking family photos of dozens of people during holidays, ordinary smartphone lenses have a limited field of view, often requiring people to squeeze together or taking multiple shots. If you want to see everyone’s facial details clearly while capturing the whole room in a single shutter click, you need a high-definition ultra-wide-angle lens.
Astronomers have faced a similar dilemma over the past three decades. Although the Hubble Space Telescope has extremely high resolution, its field of view in a single observation is only about 1/5000th the area of the full moon. It’s like looking at the night sky through a telephoto lens—getting a clear picture of a specific galaxy takes days of staring, making large-scale sky surveys nearly impossible.
On the early morning of August 30, 2026, NASA’s Nancy Grace Roman Space Telescope (a survey telescope named after the agency’s first Chief Astronomer) successfully launched aboard a Falcon Heavy rocket. Although its primary mirror has the same 2.4-meter diameter and equivalent crispness as Hubble’s, a single image covers an area of the sky 100 times larger than that of Hubble and the Webb telescope.
Sweeping the 95% Invisible Universe
The stars, planets, gas, and even the atoms in our bodies that human eyes and optical instruments can see make up only 5% of the universe’s total mass and energy. The remaining 95% belongs to an invisible world that cannot be seen directly.
This hidden 95% consists of two parts: about 27% is dark matter (an invisible glue that emits and reflects no light, holding galaxies together through gravity), and about 68% is dark energy (a mysterious, intangible repulsive force accelerating the expansion of the universe). Since they emit no light, existing observational instruments cannot capture their direct images.
As astronomer Jennifer Millard noted, scientists can see the physical effects of dark matter and dark energy, but what they actually are remains a mystery. The method to find these invisible components is to deduce their existence by observing the positional changes of hundreds of millions of galaxies over a large area. If you only stare at one or two stars in the vast night sky, you simply cannot detect the expansion of space; only by taking a snapshot of hundreds of millions of galaxies at once and observing their distribution patterns over billions of years can you trace the path of dark energy pushing and pulling the universe.
A Deep-Space Outpost 1.5 Million Kilometers Away
Early on the morning of August 30, 2026, at the Kennedy Space Center in Florida, SpaceX’s Falcon Heavy rocket roared into the sky on a giant pillar of flame. Project team leader Jackie Townsend described the launch as a magnificent dawn; about 30 minutes after liftoff, the rocket precisely delivered the telescope into its planned trajectory.
Image: Falcon Heavy rocket launching into the dawn sky. Source: NASA/John Kraus via BBC
Image: Vertical composition of the rocket liftoff. Source: Reuters via BBC
This $4.3 billion flagship facility is currently on an approximately 3-month deep-space journey. Its final destination is the Sun-Earth Lagrange Point 2 (a deep-space location about 1.5 million kilometers from Earth where the gravitational forces of the Sun and Earth reach a delicate balance). A distance of 1.5 million kilometers is roughly four times the distance from the Earth to the Moon, and the famous Webb Space Telescope also operates near this region.
This location was chosen to avoid infrared thermal interference from the Earth-Moon system. The Earth and Moon emit intense heat, and observing infrared signals in low Earth orbit is like looking for fluorescence next to bright headlights. Placing the Roman Space Telescope in the deep-space shadow zone 1.5 million kilometers away maintains an extremely low ambient temperature, enabling its infrared instruments to capture faint, ancient light from billions of light-years away.
Mapping the Universe Like Peeling an Onion
Astronomers plan to use the Roman Space Telescope’s ultra-wide field of view to create a 3D map of the universe spanning billions of light-years in depth. This map is like peeling an onion layer by layer, revealing the distribution of galaxies across different historical epochs.
As the universe continuously expands over time, the repulsive effect of dark energy in different eras leaves its mark on the clustering and spacing of galaxies. By measuring the arrangement of galaxies in different depths of these onion layers, astronomers can precisely calculate whether dark energy has pushed the expansion at a constant rate over the past few billion years, or if its strength has changed.
While surveying dark energy, the Roman Space Telescope will also facilitate many other scientific discoveries. During its expected 5 to 10-year mission, NASA official Nicola Fox anticipates that, in addition to mapping the detailed distribution of billions of galaxies, it will capture tens to hundreds of thousands of exoplanets (planets orbiting stars outside our solar system) through gravitational microlensing and deeply study the evolution of black holes.
Image: The Roman Space Telescope on display at the Goddard Space Flight Center. Source: Getty Images via BBC
From the Mother of Hubble to the Era of Panoramic Surveys
The Roman Space Telescope is named after Nancy Grace Roman (1925-2018). She was NASA’s first Chief Astronomer and a key figure in driving early space telescope projects, revered by the scientific community as the “Mother of Hubble.” Before her passing, she remarked that the Hubble telescope’s most surprising discovery was proving that the universe’s expansion is accelerating.
Today, the telescope bearing her name has officially launched. By capturing a hundredfold field of view in a single shot, the Roman telescope upgrades the previously long and tedious local sampling into a massive panoramic survey.
For the first time, humanity has achieved a high-precision panoramic view to give the universe a comprehensive checkup. Facing the 95% invisible realm, this large-scale sweeping survey will provide crucial evidence for decoding the ultimate mysteries of dark energy and dark matter.
References:
- BBC: Roman Space Telescope launch begins exploration of universe’s dark energy
- Nature: NASA’s Roman telescope mission planning and scientific goals
- NASA: Roman Space Telescope official mission overview
