The Nancy Grace Roman Space Telescope

In plain English

Imagine you are trying to map a city using a magnifying glass. You can see every brick on every building. But you can only see a tiny patch at a time. To map the whole city, you would need to move the magnifying glass thousands of times and stitch all the images together. That takes years.

Now imagine swapping the magnifying glass for a window the size of a house. You can see the entire city, maybe not every brick, but the streets, the parks, the districts, where everything is, and how it all connects. In a single glance.

That is the difference between Hubble and the Nancy Grace Roman Space Telescope.

Hubble has a tiny field of view. Its images are breathtaking because they show extraordinary detail in a narrow slice of sky. Roman will have the same image sharpness as Hubble but a field of view 100 times larger. Where Hubble needs 100 separate pointings to image a patch of sky, Roman does it in one.

The telescope is scheduled to launch in 2027. When it begins surveying, it will produce the widest, deepest maps of the universe ever assembled, and it will do so continuously, month after month, year after year.

Five things to file under "wait, what?"

• A single Roman image contains more information than a week of Hubble observations. Its detector array captures 300 megapixels per image. The deep field images it will produce will cover an area of sky 100 times larger than Hubble's famous Ultra Deep Field, which showed 10,000 galaxies in a patch of sky the size of a grain of sand held at arm's length.

• It will discover thousands of exoplanets without ever pointing directly at a star. Using a technique called microlensing, measuring the brief brightening of background stars when a planet passes between them and us, Roman will find planets that other methods cannot, including cold, distant planets similar to Neptune and Uranus orbiting far from their stars.

• It carries a coronagraph that can directly photograph planets around nearby stars. Current technology struggles to image exoplanets directly because the star they orbit is overwhelmingly bright. Roman's coronagraph blocks the starlight with extraordinary precision, opening a window onto reflected light from actual planetary surfaces.

• It is named for NASA's first Chief of Astronomy, a woman who was turned away from a physics PhD programme because of her gender. Nancy Grace Roman fought for the Hubble Space Telescope through two decades of institutional resistance. Without her persistence, Hubble would not have been built. She died in 2018 before this telescope was named in her honour.

• It will produce 20 petabytes of data over its lifetime. Processing and archiving this will require infrastructure as sophisticated as the telescope itself. All data will be made publicly available, the largest open astronomical dataset in history.

The full story

Who was Nancy Grace Roman?

Nancy Grace Roman was born in Tennessee in 1925. She knew she wanted to be an astronomer by the time she was eleven. Her high school counsellor told her that no woman had ever become a scientist and that she was wasting her time. She applied to the University of Chicago for a physics PhD. The department's response was that they preferred not to take women.

She went to the astronomy department instead and completed her PhD there. She spent years at the US Naval Observatory before joining NASA in 1959, just three months after the agency was founded. She became NASA's first Chief of Astronomy and the first woman to hold an executive position there.

Her most important contribution was pushing NASA to build a large space telescope at a time when the idea was considered expensive, ambitious to the point of absurdity, and likely to fail. What became the Hubble Space Telescope began as Roman's idea. She spent years building political and scientific support for it, navigating sceptical committees and hostile budget cycles, and she championed the development of the instruments that would eventually fly on it. She never saw it named for her. She never saw this telescope at all.

What it is designed to do

Roman has three main science programmes.

The High Latitude Wide Area Survey will map the shapes of billions of galaxies with extreme precision. Gravity distorts space; matter bends light; galaxies behind dense cosmic structures appear slightly stretched or squashed, a phenomenon called weak gravitational lensing. By measuring these distortions across billions of galaxies, Roman will map the distribution of dark matter in the universe and trace how dark energy has driven the universe's accelerating expansion over the past 10 billion years. This is the most ambitious attempt yet to understand what the universe is made of.

The High Latitude Time Domain Survey will monitor billions of stars repeatedly over time, looking for anything that changes: supernovae, variable stars, and transient events. Its primary target is Type Ia supernovae, stellar explosions that serve as precise distance markers across the cosmos. The relationship between a Type Ia supernova's brightness and its distance helped discover dark energy in 1998. Roman will measure thousands of them, refining our picture of how the universe has expanded across its lifetime.

The Galactic Bulge Time Domain Survey will stare at the dense central region of the Milky Way and watch for microlensing events, temporary brightenings caused by foreground planets passing in front of background stars. This will reveal planets at orbital distances and masses that are inaccessible to any other current method.

Why it matters beyond astronomy

The Roman Telescope represents a philosophical shift in how we survey the sky. The previous generation of great telescopes (Hubble, Chandra, Spitzer) were precision instruments aimed at specific targets. Roman is designed for survey: to map, census, and catalogue at a scale never previously attempted. The comparison to Hubble is apt but incomplete. Roman is not Hubble's successor in any direct sense. It is a different kind of tool, asking different kinds of questions.

What it will find, we do not entirely know. The history of wide-field surveys is a history of unexpected discovery: the first evidence for dark energy came from a supernova survey; the cosmic web of galaxy filaments was found by mapping large volumes of sky. Roman will map volumes that dwarf anything that came before. What is in those volumes remains, for now, unknown.

Go deeper

For the curious:

• Nancy Grace Roman Space Telescope — official site — accessible science explainers, mission timeline, and instrument descriptions from NASA.
• The Whole Shebang by Timothy Ferris — the best popular introduction to modern cosmology; contextualises what Roman is trying to measure.
• Hubble's Universe by Terence Dickinson — understanding Hubble makes the leap to Roman more vivid.

On YouTube:

• NASA Roman Telescope overview — NASA's own explainer videos cover the science goals clearly.
• Nancy Grace Roman — who she was — short documentaries on her life and her role in building Hubble.
• Dark energy explained — PBS Space Time's treatment of dark energy gives context for what Roman is trying to measure.