Light echoes are expanding shells of reflected starlight

Spikes of light around stars are artifacts of light bending around the mirror supports

Through diffraction, electromagnetic waves can bend around obstacles, as observed in the silver linings at the edges of clouds, where light should be blocked. Within reflecting telescopes, starlight diffracts around struts—beams holding a secondary mirror in place—and spreads perpendicular to them, creating pairs of spikes.

Stars appear to twinkle because turbulence in the motion of molecules in Earth's atmosphere causes light to bend and wiggle rapidly on its way to the surface—a phenomenon called scintillation.

View a gallery of Einstein rings

As light from a distant galaxy spreads in all directions, rays that pass around a massive object, such as another galaxy, may be bent around it. If the massive object is positioned between the distant galaxy and our telescopes, we may observe this deflected light forming a ring around it.

Concentrated sound waves can collapse microscopic bubbles, creating light

The phenomenon, known as sonoluminescence, can generate extremely short, high-intensity flashes from the sudden focusing of sound energy, which can drive the temperature within the bubbles to values over twice that of the sun's surface.

What are pulsars?

Pulsars are neutron stars created as part of stellar evolution and emit radiation beams visible from Earth. These beams pulse like a lighthouse's light due to the star's rotation, creating periodic high-energy emissions. Pulsars were first discovered as radio sources; it was also discovered they emit gamma rays. NASA uses its Fermi Gamma-ray Space Telescope to retrieve and analyze data from pulsars.

Oscillating matter in the early universe left behind patterns detailing cosmic expansion

As gravity tried to bring matter closer together in the early universe, its high temperature produced an outward pressure that caused it to expand. These competing forces caused matter to vibrate and produce the equivalent of sound waves, which spread outward as the universe expanded and cooled, serving as relics of dark energy's history.

Through gravitational redshift, light loses energy as it leaves a massive object

Just as one becomes exhausted as they walk up a flight of stairs against gravity, light is predicted to lose energy as it travels out of a gravitational well created by an object warping spacetime. This is observable through a decrease in the frequency of light toward longer, redder wavelengths.

Photons emitted via stimulated emission have identical characteristics

When confined to a pair of mirrors, a single photon passing a region of population-inverted atoms can produce a chain reaction of monochromatic light. This chain reaction amplifies the initial photon, from which lasers get their name: light amplification by stimulated emission of radiation.

Explaining the galaxy-sized gas bubbles hovering around the Milky Way

Depth perception is hard to achieve when looking out into space. For decades, two camps of astrophysicists have disagreed over the nature of the North Polar Spur, a radio-wave emitting arc above the Milky Way galaxy's plane. Was it close and relatively small? Or was it faraway and much more massive? New research utilizing X-ray mapping of the galaxy has helped clarify the existence of both so-called smaller Fermi bubbles and larger X-ray ones.

Light waves can interfere and cancel each other out

When light waves travel past one another, their peaks and valleys combine, just as overlapping ripples in water can combine to form a larger ripple. When the peak of a light wave meets the valley of another of the same wavelength and brightness, the waves combine to produce no light.

The finite speed of light means we can only perceive the world's past

When objects emit or reflect light, it takes time for the light to reach an observer and be detected. During the travel time, the object may have changed, limiting detections to describing the conditions of the object when the light was first emitted or reflected, before it was detected.

Fireworks make a loud booming sound after exploding due to air expanding faster than the speed of sound.

Dark stars are hypothetical stars that would have existed in the early universe

Primarily composed of visible matter, this celestial object would also contain a significant amount of dark matter that would annihilate with itself, converting its mass into energy. This energy would prevent the star from collapsing under its own gravity and from triggering nuclear fusion until its dark matter fuel was exhausted.

Voids in the northern and southern lights are known as black auroras

Appearing as dark rings or blobs against the illuminated sky, black auroras occur when there are holes in Earth's ionosphere—the upper atmospheric layer of charged particles created by solar ultraviolet rays. In these gaps—also known as anti-auroras—electrons ascend up into space, rather than spiraling into the atmosphere to collide with atmospheric gases and produce light.

Rayleigh scattering of light gives the atmosphere its blue skies and red sunsets

Light is deflected from its original path by atmospheric particles, where bluer light is scattered more than other colors. When the sun is at its highest point in the sky, it travels through the thinnest part of the atmosphere, scattering some blue light across the sky. A greater atmospheric path length at sunset scatters more colors, leaving only red, yellow, and orange.

Type Ia supernovae are 'standard candles' used to accurately measure cosmic distances

These explosions are caused by white dwarfs—remnants of low-mass stars—that reignite and explode, with every explosion brightening and dimming in the same way. By comparing them, astronomers have mapped the locations of galaxies alongside velocity data to determine the universe's expansion rate across time and the existence of dark energy.

Solar sails use light as a means of propulsion

Photons possess momentum and can transfer it to objects they strike or bounce off, imparting radiative pressure, or a light-based force over a small surface area. Lasers fired at observational equipment with specially designed sails can theoretically use this mechanism to accelerate up to 20% the speed of light.

Planeterrellas create artificial auroras that mimic the atmospheric displays of light by setting up an electric field between two metal balls in a jar filled with a small amount of air.

Cloud chambers use alcohol vapor to create trails behind passing cosmic rays

As cosmic rays travel through the air, they collide with molecules to form charged fragments called ions. Vapors in the chamber condense around these ions, creating streaks of tiny droplets that mark the paths where cosmic rays or their secondary particles traveled.

Observations of Jupiter's moons first demonstrated that light was not instantaneous

In 1676, Danish astronomer Ole Rømer noticed that eclipses of the moons occurred several minutes later when Earth and Jupiter were farther apart, reasoning that light needed more time to travel the greater distance. Lacking knowledge of Earth's orbital diameter, he was unable to calculate the speed of light.

Photons are both particles of light and messengers of the electromagnetic force

Einstein's model of light as a wave and a massless particle of energy revolutionized physics, and scientists' application of the model led to groundbreaking technologies, including medical imaging and treatments, telecommunication signals, and probes of the quantum and cosmological realms.

Shooting stars, or meteors, are fragments of asteroids and comets that burn up as they enter Earth's atmosphere, creating streaks in the sky called meteor showers.

Massive blooms of microscopic plankton called dinoflagellates produce the neon blue light seen in glowing tides.

Holograms are produced by shining light through recordings of interference patterns

When one half of a split laser beam that was reflected off the surface of an object recombines with its other, unreflected half, the two produce an interference pattern that becomes etched onto holographic film. When light shines through the back of the film, it reacts with the pattern to create the reflected light, projecting the original object.

The reflection of light within a material is the basis for fiber optics

As light travels from one material to another, it can be absorbed, reflected, or transmitted through, depending on the properties of the two materials. Fiber optic cables are designed to reflect light internally, minimizing data loss as information is sent at high speeds through flashes that represent zeros and ones.

The movement of seismic waves reveals the structure of Earth’s interior

Changes in temperature, density, and composition alter the path of primary and secondary waves, impacting where they are detected along Earth’s surface. These deflections create shadow zones 104 degrees to 140 degrees away from the epicenter, where no waves are directly detected.

What the stars once meant to ordinary people

The stars were a crucial aid for ordinary human beings in premodern societies, acting as regular timekeeping phenomena and celestial navigators. Today, light pollution and modern technology have rendered the stars a mere aesthetic delight for most of us, but their significance in history remains. Watch this brief video to learn how premodern humans used the stars for navigation, mathematics, and more.

Most of the observable universe's volume consists of voids and supervoids—enormous regions of space with little to no galaxies, stars, or light.

The Oort cloud, our solar system's theoretical icy shell

Recurring comets lead astronomers to believe they originate from an extremely distant, icy shell encapsulating the solar system. They call it the "Oort cloud," and this giant swarm of icy objects is as fascinating as it is is massive. Home of comets and a tremendous number of planetesimals, this NASA site introduces you to the Oort.

All rainbows are 'raincircles' caused by water droplets separating white sunlight into a spectrum of colors, but Earth's surface blocks the bottom half of the circle from our line of sight.

How scientists determine elemental composition based on the light emitted by cooling atoms

When electrons within an atom drop to a lower energy level closer to the nucleus, they lose energy and produce light with energy equal to the difference between the two energy levels. Because these levels and the corresponding emitted light are unique to each element, the light serves as a unique signature that can be compared to known lab samples for identification.

Hubble revealed that planet-forming disks are common around young stars

One of Hubble’s early images captured 30 young star systems in the Orion region, each surrounded by material that looked like it was forming planets. These systems increased the number of data points scientists had to test planetary formation models.

Neutron stars, the remains of some massive stars after they explode in a supernova, are the densest directly observable objects in the universe.

Dirty lightning is a thunderstorm created from friction between rising and falling flows of ash and smoke during volcanic eruptions.

The first image of a black hole was captured by creating an Earth-sized virtual observatory from a network of eight radio telescopes.

Explore the known asteroids, comets, and spacecraft involved in asteroid studies within our solar system with 'Eyes on Asteroids,' a 3D visualization from NASA.

After NASA's Voyager 1 captured Earth as a single pixel as it left the solar system in 1990, astronomer Carl Sagan used the image to reflect on humanity's fragility and the responsibility to protect 'the only world we've ever known.'

One disco producer saw 'Star Wars' four times on its opening weekend and was so inspired that he recorded the album 'Star Wars and Other Intergalactic Funk,' which produced a chart-topping single.

How fusion—which releases energy when two lighter atoms combine to form a heavier atom—differs from fission

Track the location of the Voyager probes, currently between 13 and 15 billion miles away from Earth.

Objects can be 3D printed with light by projecting 2D computerized tomography (CT) scans onto rotating cylinders of resin, which solidify upon exposure.

Explore chaos in this simulation of two double pendulums, where small differences in the release angles produce wildly different outcomes.

Browse a detailed visual analysis of over 200,000 similes—comparisons that often use 'like' or 'as'—from popular fiction to see how frequently writers the same idiomatic expressions.

The Mona Lisa's celebrity status and repeated restorations have obscured what made the painting so revolutionary for its time

How Amazon operates a 'flywheel' business model, a self-reinforcing cycle that drives continuous growth

The word 'jazz' evolved from 'jasm,' 19th-century American slang for 'energy'

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

Long before Major League Baseball began allowing instant replay for balls and strikes, an umpire reluctantly used the technology to determine whether a hit was a home run, a move that inadvertently ushered in a new era for the sport.

Researchers believe the brain consolidates memories, processes emotions, and plans for the future during dream states

Gerrymandering works through two techniques: cracking opposing voters across districts to dilute their power, and packing them into a few to waste their votes in lopsided majorities.