UNIVERSITY PARK, Pa. — On Sunday, Aug. 30, the Nancy Grace Roman Space Telescope is expected to launch from NASA’s Kennedy Space Center in Florida. The observatory will join the Hubble Space Telescope, launched in 1990, and the James Webb Space Telescope, launched in 2021, in scanning the vastness of space and potentially finding answers to longstanding mysteries of the universe.
Known as Roman, the new telescope will be able to block the starlight hiding distant exoplanets and reveal the distant disks of dust and particles that eventually give rise to new planets. Roman’s goals include completing a statistical census of planetary systems in the Milky Way and a historical analysis of how dark matter and energy — particles and forces that aren’t entirely understood — influenced the formation and evolution of the normal matter making up the universe.
In this Q&A, Christopher Palma, teaching professor of astronomy and astrophysics in Penn State’s Eberly College of Science, spoke about Roman, satellites much closer to home and what’s obscuring space observation from the Earth’s surface.
Q: What is the Nancy Grace Roman Space Telescope? How does it differ from the James Webb Space Telescope and the Hubble Space Telescope?
Palma: The telescope has some similarities to both Webb and Hubble, but it is unique in many ways. Telescopes are described by what type of light they can detect. Hubble is sensitive to ultraviolet, visible and infrared; Roman to visible and infrared; and Webb only to infrared. These different types of light can provide insight into completely different cosmic phenomena and objects, because different objects stand out more or less in one type of light versus another
The size of the observatory’s mirror also determines how sensitive the telescope is to detecting faint objects. Hubble and Roman have identical sized mirrors, about eight feet in diameter, while Webb has a much larger mirror at about 21 feet in diameter.
What really makes Roman stand out is that it is designed for wide-field imaging. The cameras on telescopes can often only detect objects in a very small patch of sky. If we use the size that the full moon appears in the sky as our guide, Hubble’s field of view is often smaller than that —meaning each picture it takes is of a patch of sky smaller than the full moon. Webb’s instruments often are even smaller than Hubble’s. Each picture taken by Roman, however, will be larger than the full moon, allowing it to survey more of the sky much faster than Hubble or Webb.
Q: The Nancy Grace Roman Space Telescope will join Webb in orbiting the sun almost one million miles from Earth, but Hubble circles Earth in “low Earth orbit.” What does that mean?
Palma: To set the scale, the moon is about 250,000 miles or 400,000 kilometers from Earth. Most folks picture telescopes and satellites quite far from Earth — they often think they are about halfway between the Earth and the moon. In reality, they are in low Earth orbit, which is about 0.25% of the way to the moon.
Low Earth orbit often means something like 500 to 2,000 kilometers, or roughly 310 to 1,250 miles, above Earth. In comparison, that’s at least 44 times higher than cruising altitude for most commercial flights. So, low Earth orbit is much higher than planes fly, but it is much, much closer than the moon.
Q: What else is sent to low Earth orbit? How crowded is this area getting, and how might that impact life on Earth?
Palma: There are many satellites in low Earth orbit. These can be for research purposes, communications purposes, or military purposes, for example. Other things we launch into space, like expended rocket bodies, wind up in these orbits, too. There is debris like small pieces of destroyed satellites, and there are natural objects like meteoroids that pass through low Earth orbit.
It is already crowded, but many companies want to build and launch many thousands up to a million satellites in the next decade or so. There is a lot of concern among astronomers about how these satellites may negatively impact our ability to see beyond the Earth. Beyond satellites, there are other companies focused on using low Earth orbit for other reasons — one particular project causing significant concerns involves launching space mirrors to light up large swaths of the Earth.
While space and the ability to see the sky beyond are areas of significant worry, there is also concern that a catastrophic collision could result as satellites become more prevalent. Such a collision might create a chain reaction that destroys most of the artificial objects in orbit, cutting those on Earth off from space and from each other in terms of telecommunications. Called Kessler syndrome, the theoretical scenario has been depicted in such fiction as the movie “Gravity” but has real scientific analysis underpinning the possibility.
Q: Back on Earth, reports indicate that light pollution has caused the brightness of the night sky — which can obscure stars and planetary bodies — to more than double from 2011 to 2022. What is light pollution? Can it be mitigated?
Palma: There is increasing crowding in low Earth orbit, but light pollution on Earth’s surface is what really prevents us from seeing the night sky, and we can blame ALAN: artificial light at night.
All of our lighting that points upward is lighting up the sky, making the night sky much brighter than it would be without these lights. One way to characterize the scope of the problem in any particular place is to estimate how many stars you can see on a moonless night. Without light pollution, a good human eye can detect a few thousand stars. However, in downtown New York City, you might see a dozen. In more suburban locations like State College, we may see a few hundred stars on a good, dark night, but that’s a change from a few decades ago, when we used to be able to see the Milky Way.
There are ways to mitigate light pollution: shielding lights, using timers or motion sensors, reducing the amount of light you install, and using lights that give off more orange and red and less blue and white light. Many areas around the world, including France and parts of Australia, have shown that common sense restrictions on lights can dramatically improve the night sky. In particular, Flagstaff, Arizona — the home of Lowell Observatory, where Pluto was discovered — has been very successful in reducing their light pollution using these approaches and describes their sky as 90% darker than the similarly sized community of Cheyenne in Wyoming. They claim that you can see the Milky Way within the city limits, which is unheard of in 2026 for most communities larger than a few thousand people.