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By NASA
4 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
A NASA researcher and innovation architect from the Convergent Aeronautics Solutions project Discovery team collaborating at a whiteboard during a visit to Chapel Hill, N.C. on Aug. 13, 2024.NASA / Ariella Knight Convergent Aeronautics Solutions (CAS) Discovery identifies problems worth solving for the benefit of all.
We formulate “convergent” problems—across multiple disciplines and sectors—and build footholds toward potentially transformative opportunities in aeronautics. As aeronautics rapidly advances, it is increasingly intersecting with other sectors like energy, healthcare, emergency response, economic resilience, the space economy, and more.
CAS Discovery builds new innovation tools and methods, a workforce adept at innovation methods, and transdisciplinary teams of researchers within and beyond NASA that conduct regular “Discovery sprints”—expeditions into cross-sector topic areas that could beneficially transform aeronautics and humanity.
WHAT is Discovery?
Participatory
It is difficult to understand and effectively address stakeholders’ needs & capabilities without engaging them. Discovery, in consultation with key NASA offices and other government agencies, has honed mechanisms to lawfully and respectfully engage and invite participation from stakeholders, communities, industry, NGOs and government to collaboratively formulate complex societal challenges tied to aviation.
Convergent
Typical organizational structures limit convergence across knowledge boundaries. CAS Discovery is intentionally cross-sector and transdisciplinary because the most impactful ideas often lie at the intersection of boundaries, the borderlands where multiple disciplines and communities come together. We work to emerge multi-sector, system-of-systems challenges that integrate political, economic, social, technological, environmental, legal and ethical trends, needs, and capabilities.
Future-Focused
Organizations have a tendency of being driven by short-term thinking and relatively short time horizons. CAS Discovery uses strategic foresight methods to examine 20 to 50-year time horizons, systematically ingesting and synthesizing signals and trends from aero and non-aero sources to envision a variety of scenarios to uncover opportunities for the future of aeronautics.
Ecosystemic
We study the ecosystems that are part of aeronautics and aerospace. This helps in broadening consideration of impacts while practicing foresight. It enhances our awareness of the environment and gives stakeholders the ability to see ripple effects across technologies, economies, communities, etc. We seek to benefit the wellness of the entire ecosystem while also benefiting the constituents.
A group of NASA researchers and leaders from the Convergent Aeronautics Solutions project Discovery team at the agency’s Glenn Research Center in Cleveland, on April 30, 2024.NASA / Ricaurte Chock WHO is Discovery?
NASA Researchers
They are the engine that propels CAS Discovery. Our cross-center Discovery sprint and foresight teams are composed of researchers from NASA’s Ames Research Center and Armstrong Flight Research Center in California, Glenn Research Center in Cleveland, and Langley Research Center in Virginia.
Researchers from Outside of NASA
They collaborate with us as subject matter experts or Discovery sprint team members to contribute their backgrounds in fields less common within NASA, such as energy, economics, anthropology, and other areas. This collaboration happens through many mechanisms, such as freelancing, crowdsourcing, interviews, webinars, and podcasts.
Stakeholders
They are engaged in various ways and to different degrees, often co-envisioning potential futures, co-formulating problems, and co-designing solutions.
Innovation Architects
They are the glue that holds CAS Discovery together and the anti-glue that keeps our teams from getting stuck. They come from a wide range of experience, each bringing deep expertise in leading transdisciplinary teams and stakeholders through processes and methods from strategic foresight, complex systems design, human-centered design, and more.
CAS Center Integration Leads (CILs)
They work with NASA line management at each Aeronautics center to bring NASA researchers and potential new PIs into CAS. CILs also host annual Wicked Wild idea pitch events to bring new problem areas and solution ideas into CAS Discovery and early Execution phases.
Ames Research Center CIL: Ty Huang Armstrong Flight Research Center CIL: Matt Kearns Glenn Research Center CIL: Jeffrey Chin Langley Research Center CIL: Devin Pugh-Thomas CAS Discovery Leads
They oversee Discovery sprint and strategic foresight teams, topics, and processes; new tools and continuous improvement experiments; and the overall health of the CAS innovation front-end pipeline and related strategic outputs.
Discovery Lead: Eric Reynolds Brubaker, Langley Research Center Foresight Lead: Vikram Shyam, Glenn Research Center Sample Discovery Publications
COMING SOON: Links to Technical Memorandums and conference papers.
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Last Updated Mar 21, 2025 EditorJim BankeContactDiana Fitzgeralddiana.r.fitzgerald@nasa.gov Related Terms
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By NASA
Artist’s rendering of a potentially habitable super-Earth orbiting a star called HD 20794. Illustration credit: Gabriel Pérez Díaz, SMM (IAC) The Discovery
A possible “super-Earth” orbits a relatively close, Sun-like star, and could be a habitable world – but one of extreme temperature swings, from scorching heat to deep freeze.
Key Facts
The newly confirmed planet is the outermost of three detected so far around a star called HD 20794, just 20 light-years from Earth. Its 647-day orbit is comparable to Mars in our solar system. But this planet’s orbit is highly eccentric, stretched into an oval shape. That brings the planet close enough to the star to experience runaway heating for part of its year, then carries it far enough away to freeze any potential water on its surface. The planet has been bouncing between these extremes roughly every 300 days – perhaps for billions of years.
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The planet spends a good chunk of its year in the “habitable zone” around its star, the orbital distance that would allow liquid water to form on the surface under the right atmospheric conditions. But because of its eccentric orbit, it moves to a distance interior to the inner edge of the habitable zone when closest to the star, and outside the outer edge when farthest away. At its closest, the planet’s distance from the star is comparable to Venus’s distance from the Sun; at its farthest point, it is nearly twice the distance from Earth to the Sun. The planet is possibly rocky, like Earth, but could be a heftier version – about six times as massive as our home planet.
Star HD 20794 and its posse of possible planets have been extensively studied, but the international team of astronomers that confirmed the outer planet, led by Nicola Nari of Light Bridges S.L. and the Instituto de Astrofisica de Canarias, examined more than 20 years worth of data to pin down all three planets’ orbits and likely masses.
The scientists relied on data from two ground-based, precision instruments: HARPS, the High Accuracy Radial velocity Planet Searcher in La Silla, Chile, and ESPRESSO, the Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations in Paranal, Chile. Both instruments, connected to powerful telescopes, measure tiny shifts in the light spectrum of stars, caused by the gravity of planets tugging the star back and forth as they orbit.
But such tiny shifts in the star’s spectrum also can be caused by imposters – spots, flares, or other activity on the star’s surface, carried along as the star rotates and masquerading as orbiting planets. The science team spent years painstakingly analyzing the spectrum shifts, or “radial velocity” data, for any sign of background noise or even jitters from the instruments themselves. They confirmed the reputation of HD 20794 as a fairly quiet star, not prone to outbursts that might be confused for signs of orbiting planets.
Fun Facts
The elliptically orbiting super-Earth appears to be an ideal target for future space-based telescopes designed to search for habitable worlds, seeking possible signs of life. High on the list is NASA’s Habitable Worlds Observatory, which will someday examine the atmospheres of Earth-sized planets around Sun-like stars. When launched in the decades ahead, the observatory would spread the light from such planets into a spectrum to determine which gases are present – including those that might reveal some form of life. The relative closeness of HD 20974, only 20 light-years away, its brightness, and its low level of surface activity – not to mention the third planet’s wild temperature swings – could make this system a prime candidate for scrutiny by HWO.
The Discoverers
The international science team that confirmed the eccentric super-Earth was led by researcher Nicola Nari of the Light Bridges S.L. and the Instituto de Astrofisica de Canarias, and included Dr. Michael Cretignier of the University of Oxford, who first picked up the potential planet’s signal in 2022. Their paper, “Revisiting the multi-planet system of the nearby star HD 20794,” was published online by the journal, Astronomy and Astrophysics, in January 2025.
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By NASA
X-ray: NASA/CXC/SAO/Univ Mexico/S. Estrada-Dorado et al.; Ultraviolet: NASA/JPL; Optical: NASA/ESA/STScI (M. Meixner)/NRAO (T.A. Rector); Infrared: ESO/VISTA/J. Emerson; Image Processing: NASA/CXC/SAO/K. Arcand; A planet may have been destroyed by a white dwarf at the center of a planetary nebula — the first time this has been seen. As described in our latest press release, this would explain a mysterious X-ray signal that astronomers have detected from the Helix Nebula for over 40 years. The Helix is a planetary nebula, a late-stage star like our Sun that has shed its outer layers leaving a small dim star at its center called a white dwarf.
This composite image contains X-rays from Chandra (magenta), optical light data from Hubble (orange, light blue), infrared data from ESO (gold, dark blue), and ultraviolet data from GALEX (purple) of the Helix Nebula. Data from Chandra indicates that this white dwarf has destroyed a very closely orbiting planet.
This artist’s impression shows a planet (left) that has approached too close to a white dwarf (right) and been torn apart by tidal forces from the star. The white dwarf is in the center of a planetary nebula depicted by the blue gas in the background. The planet is part of a planetary system, which includes one planet in the upper left and another in the lower right. The besieged planet could have initially been a considerable distance from the white dwarf but then migrated inwards by interacting with the gravity of other planets in the system.CXC/SAO/M.Weiss An artist’s concept shows a planet (left) that has approached too close to a white dwarf (right) and is being torn apart by tidal forces from the star. The white dwarf is in the center of a planetary nebula depicted by the blue gas in the background. The planet is part of a planetary system, which includes one planet in the upper left and another in the lower right. The besieged planet could have initially been a considerable distance from the white dwarf but then migrated inwards by interacting with the gravity of the other planets in the system.
Eventually debris from the planet will form a disk around the white dwarf and fall onto the star’s surface, creating the mysterious signal in X-rays that astronomers have detected for decades.
Dating back to 1980, X-ray missions, such as the Einstein Observatory and ROSAT telescope, have picked up an unusual reading from the center of the Helix Nebula. They detected highly energetic X-rays coming from the white dwarf at the center of the Helix Nebula named WD 2226-210, located only 650 light-years from Earth. White dwarfs like WD 2226-210 do not typically give off strong X-rays.
In about 5 billion years, our Sun will run out of fuel and expand, possibly engulfing Earth. These end stages of a star’s life can be utterly beautiful as is the case with this planetary nebula called the Helix Nebula.X-ray: NASA/CXC/SAO/Univ Mexico/S. Estrada-Dorado et al.; Ultraviolet: NASA/JPL; Optical: NASA/ESA/STScI (M. Meixner)/NRAO (T.A. Rector); Infrared: ESO/VISTA/J. Emerson; Image Processing: NASA/CXC/SAO/K. Arcand; A new study featuring the data from Chandra and XMM-Newton may finally have settled the question of what is causing these X-rays from WD 2226-210: this X-ray signal could be the debris from a destroyed planet being pulled onto the white dwarf. If confirmed, this would be the first case of a planet seen to be destroyed by the central star in a planetary nebula.
Observations by ROSAT, Chandra, and XMM-Newton between 1992 and 2002 show that the X-ray signal from the white dwarf has remained approximately constant in brightness during that time. The data, however, suggest there may be a subtle, regular change in the X-ray signal every 2.9 hours, providing evidence for the remains of a planet exceptionally close to the white dwarf.
Previously scientists determined that a Neptune-sized planet is in a very close orbit around the white dwarf — completing one revolution in less than three days. The researchers in this latest study conclude that there could have been a planet like Jupiter even closer to the star. The besieged planet could have initially been a considerable distance from the white dwarf but then migrated inwards by interacting with the gravity of other planets in the system. Once it approached close enough to the white dwarf the gravity of the star would have partially or completely torn the planet apart.
WD 2226-210 has some similarities in X-ray behavior to two other white dwarfs that are not inside planetary nebulas. One is possibly pulling material away from a planet companion, but in a more sedate fashion without the planet being quickly destroyed. The other white dwarf is likely dragging material from the vestiges of a planet onto its surface. These three white dwarfs may constitute a new class of variable, or changing, object.
A paper describing these results appears in The Monthly Notices of the Royal Astronomical Society and is available online. The authors of the paper are Sandino Estrada-Dorado (National Autonomous University of Mexico), Martin Guerrero (The Institute of Astrophysics of Andalusia in Spain), Jesús Toala (National Autonomous University of Mexico), Ricardo Maldonado (National Autonomous University of Mexico), Veronica Lora (National Autonomous University of Mexico), Diego Alejandro Vasquez-Torres (National Autonomous University of Mexico), and You-Hua Chu (Academia Sinica in Taiwan).
NASA’s Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.
Read more from NASA’s Chandra X-ray Observatory.
Learn more about the Chandra X-ray Observatory and its mission here:
https://www.nasa.gov/chandra
https://chandra.si.edu
Visual Description
This release features two images; a composite image of the Helix Nebula, and an artist’s rendering of a planet’s destruction, which may be occurring in the nebula’s core.
The Helix Nebula is a cloud of gas ejected by a dying star, known as a white dwarf. In the composite image, the cloud of gas strongly resembles a creature’s eye. Here, a hazy blue cloud is surrounded by misty, concentric rings of pale yellow, rose pink, and blood orange. Each ring appears dusted with flecks of gold, particularly the outer edges of the eye-shape.
The entire image is speckled with glowing dots in blues, whites, yellows, and purples. At the center of the hazy blue gas cloud, a box has been drawn around some of these dots including a bright white dot with a pink outer ring, and a smaller white dot. The scene which may be unfolding inside this box has been magnified in the artist’s rendering.
The artist’s digital rendering shows a possible cause of the large white dot with the pink outer ring. A brilliant white circle near our upper right shows a white dwarf, the ember of a dying star. At our lower left, in the relative foreground of the rendering, is what remains of a planet. Here, the planet resembles a giant boulder shedding thousands of smaller rocks. These rocks flow off the planet’s surface, pulled back toward the white dwarf in a long, swooping tail. Glowing orange fault lines mar the surface of the crumbling planet. In our upper left and lower right, inside the hazy blue clouds which blanket the rendering, are two other, more distant planets. After the rocks from the planet start striking the surface of the white dwarf, X-rays should be produced.
News Media Contact
Megan Watzke
Chandra X-ray Center
Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu
Lane Figueroa
Marshall Space Flight Center, Huntsville, Alabama
256-544-0034
lane.e.figueroa@nasa.gov
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By NASA
5 Min Read Planetary Alignments and Planet Parades
A sky chart showing Mars, Jupiter, Saturn, and Venus in a “planet parade.” Credits:
NASA/JPL-Caltech On most nights, weather permitting, you can spot at least one bright planet in the night sky. While two or three planets are commonly visible in the hours around sunset, occasionally four or five bright planets can be seen simultaneously with the naked eye. These events, often called “planet parades” or “planetary alignments,” can generate significant public interest. Though not exceedingly rare, they’re worth observing since they don’t happen every year.
Why Planets Appear Along a Line in The Sky
“Planet parade” isn’t a technical term in astronomy, and “planetary alignment” can refer to several different phenomena. As the planets of our solar system orbit the Sun, they occasionally line up in space in events called oppositions and conjunctions. A planetary alignment can also refer to apparent lineups in our sky with other planets, the Moon, or bright stars.
The planets of our solar system always appear along a line on the sky. This line, referred to as the ecliptic, represents the plane in which the planets orbit, seen from our position within the plane itself. NASA/Preston Dyches When it comes to this second type of planetary alignment, it’s important to understand that planets always appear along a line or arc across the sky. This occurs because the planets orbit our Sun in a relatively flat, disc-shaped plane. From Earth, we’re looking into that solar system plane from within. We see the racetrack of the planets from the perspective of one of the racers ourselves. When viewed edge-on, this disc appears as a line, which we call the ecliptic or ecliptic plane.
So, while planet alignment itself isn’t unusual, what makes these events special is the opportunity to observe multiple planets simultaneously with the naked eye.
Will the Planets Actually be Visible?
Before preparing to observe a planet parade, we have to consider how high the planets will appear above the horizon. For most observers to see a planet with the naked eye, it needs to be at least a few degrees above the horizon, and10 degrees or higher is best. This is crucial because Earth’s atmosphere near the ground dims celestial objects as they rise or set. Even bright planets become difficult or impossible to spot when they’re too low, as their light gets scattered and absorbed on its path to your eye. Buildings, trees, and other obstructions often block the view near the horizon as well.
This visibility challenge is particularly notable after sunset or before sunrise, where the sky is still glowing. If a planet appears very low within the sunset glow, it is very difficult to observe.
The Planets You Can See, and Those You Can’t
Five planets are visible without optical aid: Mercury, Venus, Mars, Jupiter, and Saturn. Ancient civilizations recognized these worlds as bright lights that wandered across the starscape, while the background stars remained fixed in place. In fact, the word “planet” comes to us from the Greek word for “wanderer.”
The solar system includes two additional major planets, Uranus and Neptune, plus numerous dwarf planets like Pluto and Ceres. Uranus and Neptune orbit in the dim, cold depths of the outer solar system. Neptune absolutely requires a telescope to observe. While Uranus is technically bright enough to detect with good eyesight, it’s quite faint and requires dark skies and precise knowledge of its location among similarly faint stars, so a telescope is recommended. As we’ll discuss in the next section, planet parades necessarily must be observed in twilight before dawn or after sunset, and this is not a good time to try observing extremely faint objects like Uranus and Neptune.
Thus, claims about rare six- or seven-planet alignments which include Uranus and Neptune should be viewed with the understanding that these two distant planets will not be visible to the unaided eye.
What Makes Multi-Planet Lineups Special
Lineups of four or five planet naked-eye planets with optimal visibility typically occur every few years. Mars, Jupiter, and Saturn are frequently seen in the night sky, but the addition of Venus and Mercury make four- and five-planet lineups particularly noteworthy. Both orbit closer to the Sun than Earth, with smaller, faster orbits than the other planets. Venus is visible for only a couple of months at a time when it reaches its greatest separation from the Sun (called elongation), appearing just after sunset or before sunrise. Mercury, completing its orbit in just 88 days, is visible for only a couple of weeks (or even a few days) at a time just after sunset or just before sunrise.
Planet parades aren’t single-day events, as the planets move too slowly for that. Generally, multi-planet viewing opportunities last for weeks to a month or more. Even five-planet events last for several days as Mercury briefly emerges from and returns to the Sun’s glare.
In summary, while they aren’t once-in-a-lifetime events, planetary parades afford an uncommon opportunity to look up and appreciate our place in our solar system, with diverse worlds arrayed across the sky before our very eyes.
Other Planet Lineups
Other recent and near-future multi-planet viewing opportunities:
January 2016 – Four planets visible at once before sunrise Late April to Late August 2022 – Four planets visible at once before sunrise Mid-June to Early July 2022 – Five planets visible at once before sunrise January to mid-February 2025 – Four planets visible at once after sunset Late August 2025 – Four planets visible at once before sunrise Late October 2028 – Five planets visible at once before sunrise Late February 2034 – Five planets visible at once after sunset (Venus and Mercury challenging to observe) About the January/February 2025 Planet Parade
The current four-planet lineup concludes by mid-February, as Saturn sinks increasingly lower in the sky each night after sunset. By mid-to-late February, Saturn appears less than 10 degrees above the horizon as sunset fades, making it difficult to observe for most people. While Mercury briefly joins Saturn in the post-sunset glow at the end of February, both planets will be too low and faint for most observers to spot.
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By NASA
Hubble Space TelescopeHubble Home OverviewAbout Hubble The History of Hubble Hubble Timeline Why Have a Telescope in Space? Hubble by the Numbers At the Museum FAQs Impact & BenefitsHubble’s Impact & Benefits Science Impacts Cultural Impact Technology Benefits Impact on Human Spaceflight Astro Community Impacts ScienceHubble Science Science Themes Science Highlights Science Behind Discoveries Hubble’s Partners in Science Universe Uncovered Explore the Night Sky ObservatoryHubble Observatory Hubble Design Mission Operations Missions to Hubble Hubble vs Webb TeamHubble Team Career Aspirations Hubble Astronauts NewsHubble News Hubble News Archive Social Media Media Resources MultimediaMultimedia Images Videos Sonifications Podcasts e-Books Online Activities Lithographs Fact Sheets Glossary Posters Hubble on the NASA App More35th Anniversary 7 Min Read NASA Celebrates Edwin Hubble’s Discovery of a New Universe
The Cepheid variable star, called V1, in the neighboring Andromeda galaxy. Credits: NASA, ESA, Hubble Heritage Team (STScI/AURA); Acknowledgement: R. Gendler For humans, the most important star in the universe is our Sun. The second-most important star is nestled inside the Andromeda galaxy. Don’t go looking for it — the flickering star is 2.2 million light-years away, and is 1/100,000th the brightness of the faintest star visible to the human eye.
Yet, a century ago, its discovery by Edwin Hubble, then an astronomer at Carnegie Observatories, opened humanity’s eyes as to how large the universe really is, and revealed that our Milky Way galaxy is just one of hundreds of billions of galaxies in the universe ushered in the coming-of-age for humans as a curious species that could scientifically ponder our own creation through the message of starlight. Carnegie Science and NASA are celebrating this centennial at the 245th meeting of the American Astronomical Society in Washington, D.C.
The seemingly inauspicious star, simply named V1, flung open a Pandora’s box full of mysteries about time and space that are still challenging astronomers today. Using the largest telescope in the world at that time, the Carnegie-funded 100-inch Hooker Telescope at Mount Wilson Observatory in California, Hubble discovered the demure star in 1923. This rare type of pulsating star, called a Cepheid variable, is used as milepost markers for distant celestial objects. There are no tape-measures in space, but by the early 20th century Henrietta Swan Leavitt had discovered that the pulsation period of Cepheid variables is directly tied to their luminosity.
Many astronomers long believed that the edge of the Milky Way marked the edge of the entire universe. But Hubble determined that V1, located inside the Andromeda “nebula,” was at a distance that far exceeded anything in our own Milky Way galaxy. This led Hubble to the jaw-dropping realization that the universe extends far beyond our own galaxy.
In fact Hubble had suspected there was a larger universe out there, but here was the proof in the pudding. He was so amazed he scribbled an exclamation mark on the photographic plate of Andromeda that pinpointed the variable star.
In commemoration of Edwin Hubble’s discovery of a Cepheid variable class star, called V1, in the neighboring Andromeda galaxy 100 years ago, astronomers partnered with the American Association of Variable Star Observers (AAVSO) to study the star. AAVSO observers followed V1 for six months, producing a plot, or light curve, of the rhythmic rise and fall of the star’s light. Based on this data, the Hubble Space Telescope was scheduled to capture the star at its dimmest and brightest light. Edwin Hubble’s observations of V1 became the critical first step in uncovering a larger, grander universe than some astronomers imagined at the time. Once dismissed as a nearby “spiral nebula” measurements of Andromeda with its embedded Cepheid star served as a stellar milepost marker. It definitively showed that Andromeda was far outside of our Milky Way. Edwin Hubble went on to measure the distances to many galaxies beyond the Milky Way by finding Cepheid variables within those levels. The velocities of those galaxies, in turn, allowed him to determine that the universe is expanding.NASA, ESA, Hubble Heritage Team (STScI/AURA); Acknowledgment: R. Gendler As a result, the science of cosmology exploded almost overnight. Hubble’s contemporary, the distinguished Harvard astronomer Harlow Shapley, upon Hubble notifying him of the discovery, was devastated. “Here is the letter that destroyed my universe,” he lamented to fellow astronomer Cecilia Payne-Gaposchkin, who was in his office when he opened Hubble’s message.
Just three years earlier, Shapley had presented his observational interpretation of a much smaller universe in a debate one evening at the Smithsonian Museum of Natural History in Washington. He maintained that the Milky Way galaxy was so huge, it must encompass the entirety of the universe. Shapley insisted that the mysteriously fuzzy “spiral nebulae,” such as Andromeda, were simply stars forming on the periphery of our Milky Way, and inconsequential.
Little could Hubble have imagined that 70 years later, an extraordinary telescope named after him, lofted hundreds of miles above the Earth, would continue his legacy. The marvelous telescope made “Hubble” a household word, synonymous with wonderous astronomy.
Today, NASA’s Hubble Space Telescope pushes the frontiers of knowledge over 10 times farther than Edwin Hubble could ever see. The space telescope has lifted the curtain on a compulsive universe full of active stars, colliding galaxies, and runaway black holes, among the celestial fireworks of the interplay between matter and energy.
Edwin Hubble was the first astronomer to take the initial steps that would ultimately lead to the Hubble Space Telescope, revealing a seemingly infinite ocean of galaxies. He thought that, despite their abundance, galaxies came in just a few specific shapes: pinwheel spirals, football-shaped ellipticals, and oddball irregular galaxies. He thought these might be clues to galaxy evolution – but the answer had to wait for the Hubble Space Telescope’s legendary Hubble Deep Field in 1994.
The most impactful finding that Edwin Hubble’s analysis showed was that the farther the galaxy is, the faster it appears to be receding from Earth. The universe looked like it was expanding like a balloon. This was based on Hubble tying galaxy distances to the reddening of light — the redshift – that proportionally increased the father away the galaxies are.
The redshift data were first collected by Lowell Observatory astronomer Vesto Slipher, who spectroscopically studied the “spiral nebulae” a decade before Hubble. Slipher did not know they were extragalactic, but Hubble made the connection. Slipher first interpreted his redshift data an example of the Doppler effect. This phenomenon is caused by light being stretched to longer, redder wavelengths if a source is moving away from us. To Slipher, it was curious that all the spiral nebulae appeared to be moving away from Earth.
Two years prior to Hubble publishing his findings, the Belgian physicist and Jesuit priest Georges Lemaître analyzed the Hubble and Slifer observations and first came to the conclusion of an expanding universe. This proportionality between galaxies’ distances and redshifts is today termed Hubble–Lemaître’s law.
Because the universe appeared to be uniformly expanding, Lemaître further realized that the expansion rate could be run back into time – like rewinding a movie – until the universe was unimaginably small, hot, and dense. It wasn’t until 1949 that the term “big bang” came into fashion.
This was a relief to Edwin Hubble’s contemporary, Albert Einstein, who deduced the universe could not remain stationary without imploding under gravity’s pull. The rate of cosmic expansion is now known as the Hubble Constant.
Ironically, Hubble himself never fully accepted the runaway universe as an interpretation of the redshift data. He suspected that some unknown physics phenomenon was giving the illusion that the galaxies were flying away from each other. He was partly right in that Einstein’s theory of special relativity explained redshift as an effect of time-dilation that is proportional to the stretching of expanding space. The galaxies only appear to be zooming through the universe. Space is expanding instead.
Compass and scale image titled “Cepheid Variable Star V1 in M31 HST WFC3/UVIS.” Four boxes each showing a bright white star in the center surrounded by other stars. Each box has a correlating date at the bottom: Dec. 17, 2020, Dec. 21, 2010, Dec. 30, 2019, and Jan. 26, 2011. The center star in the boxes appears brighter with each passing date.NASA, ESA, Hubble Heritage Project (STScI, AURA) After decades of precise measurements, the Hubble telescope came along to nail down the expansion rate precisely, giving the universe an age of 13.8 billion years. This required establishing the first rung of what astronomers call the “cosmic distance ladder” needed to build a yardstick to far-flung galaxies. They are cousins to V1, Cepheid variable stars that the Hubble telescope can detect out to over 100 times farther from Earth than the star Edwin Hubble first found.
Astrophysics was turned on its head again in 1998 when the Hubble telescope and other observatories discovered that the universe was expanding at an ever-faster rate, through a phenomenon dubbed “dark energy.” Einstein first toyed with this idea of a repulsive form of gravity in space, calling it the cosmological constant.
Even more mysteriously, the current expansion rate appears to be different than what modern cosmological models of the developing universe would predict, further confounding theoreticians. Today astronomers are wrestling with the idea that whatever is accelerating the universe may be changing over time. NASA’s Roman Space Telescope, with the ability to do large cosmic surveys, should lead to new insights into the behavior of dark matter and dark energy. Roman will likely measure the Hubble constant via lensed supernovae.
This grand century-long adventure, plumbing depths of the unknown, began with Hubble photographing a large smudge of light, the Andromeda galaxy, at the Mount Wilson Observatory high above Los Angeles.
In short, Edwin Hubble is the man who wiped away the ancient universe and discovered a new universe that would shrink humanity’s self-perception into being an insignificant speck in the cosmos.
The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
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Edwin Hubble Hubble Views the Star That Changed the Universe The History of Hubble Facebook logo @NASAHubble @NASAHubble Instagram logo @NASAHubble Media Contact:
Claire Andreoli (claire.andreoli@nasa.gov)
NASA’s Goddard Space Flight Center, Greenbelt, MD
Ray Villard
Space Telescope Science Institute, Baltimore, MD
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Last Updated Jan 15, 2025 EditorAndrea GianopoulosLocationNASA Goddard Space Flight Center Related Terms
Andromeda Galaxy Astrophysics Astrophysics Division Goddard Space Flight Center Hubble Space Telescope Stars The Universe Keep Exploring Discover More Topics From Hubble
Hubble Space Telescope
Since its 1990 launch, the Hubble Space Telescope has changed our fundamental understanding of the universe.
Discovering a Runaway Universe
Our cosmos is growing, and that expansion rate is accelerating.
The History of Hubble
Hubble’s Night Sky Challenge
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