Astronomers use a set of scaffolding methods to measure distances across the universe

How do scientists study far away stars?

Astronomy is the only science that is purely observational: meaning, scientists can't study stars in a lab. Here's a breakdown of how modern researchers use new tools to understand objects billions of light years away. As it turns out, the rules of science allow us to identify, categorize, and experiment with phenomena light years away.

Astronomers use a star's color to determine how fast it's moving

According to the Doppler Effect, light from objects moving away from Earth shifts toward the red end of the electromagnetic spectrum, with the severity of the shift correlating to recession speed. Due to the universe's expansion, light from the most distant galaxies can be moved from ultraviolet to infrared.

There are statistically significant discrepancies in measured universal expansion

Using data from the cosmic microwave background, which allows astronomers to model the universe's conditions since its earliest moments, yields a rate of expansion—the Hubble constant—lower than values obtained from multiple techniques measured locally at more recent timescales. Reconciling the discrepancy, known as the Hubble tension, will require a third independent measurement method between the two scales

Explore our favorite visualization of the immense scale of space, from an astronaut to the size of the observable universe

Four astronomical discoveries from ancient Greece

Modern astronomy relies on making discoveries without being present on the planets, stars, galaxies, and other objects studied. Imagine the difficulty the ancient Greeks had studying them without computers and telescopes. Yet somehow they calculated precise measurements of planetary distances, sizes, and more. Read this page to learn more about early triumphs in astronomical science.

How atomic clocks have been used to measure the universe's fundamental constants

Atoms behave according to a set of parameters that scientists have determined give reality its properties. For example, the fine-structure constant, α, quantifies the strength of interactions between charged particles. Since the light emitted by atoms as they move between energy levels is affected by α, analyzing these emissions—the basis of atomic clocks—using different atoms helps calculate α.

See to the edge of the universe with this two-decade astronomy project

A New Mexico telescope has captured astronomical data for two decades to compile this map of the universe. Starting from earth and ending at the "edge" of the universe, it shows one slice of the cosmos: a total of 200,000 galaxies.

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.

Asteroids are often unobserved until they are days away from Earth

Even those large enough to cause local or regional damage are too small, dim, and far away to be observed readily from cosmological distances. New tools, like NASA's NEO Surveyor telescope, aim to address gaps in detection systems.

DESI is mapping the universe's expansion over the last 11 billion years

The Dark Energy Spectroscopic Instrument is conducting a five-year redshift survey of over one-third of the sky, measuring the receding motions and locations of about 35 million galaxies and millions of stars using light captured by 5,000 optical fibers.

Explore how far you've traveled through space while living on Earth

Using the "Cosmic Odometer," users can enter their birthday and learn how far they have moved through space due to the combined effects of Earth's rotation around its axis, the planet's orbit around the sun, the solar system's trajectory through the Milky Way, and the galaxy's motion through the universe.

Gaia mapped two billion stars in the Milky Way

Using geometric parallax, the European Space Agency mission made position measurements accurate to 2.78 × 10⁻¹⁰ degrees, revealing large-scale galactic structure and dynamics. Remnants of ancient galactic mergers were also identified within the Milky Way.

The European Space Agency's Euclid telescope maps dark matter

As light rays travel near massive objects in space, their paths can be distorted on their way to Earth, causing objects to appear displaced, magnified, shrunken, or sheared. By simulating these effects for various mass distributions, astronomers can match the distortion to a simulated mass and compare it with the observed visible matter to infer the presence of dark matter.

Explore the scale of the universe in this interactive adventure

The sheer enormity of the universe escapes our ability to conceive of its scale, despite the best efforts of human imagination. This interactive provides an intuitive sense of how small we are, from a single astronaut to the Milky Way and beyond.

New ways of seeing the cosmos have redrawn the map of human identity

From Galileo’s crude spyglass to the James Webb Space Telescope, each technological leap has expanded our observational reach and redefined philosophical and moral conceptions of our place in the universe. Identifying signs of life through the study of exoplanet atmospheres would represent the next great revolution.

The Hubble Space Telescope is named after astronomer Edwin Powell Hubble

Using the Hooker Telescope at the Mount Wilson Observatory in California in the 1920s, Hubble identified Cepheid variable stars in what was believed to be the Andromeda nebula. These stars can be used to determine distance in space, allowing Hubble to realize that Andromeda was a galaxy of its own.

Earth's circumference was estimated over 2,000 years ago using geometry and shadows

By measuring the angle of the shadow cast in Syene when no shadow was cast in Alexandria, Eratosthenes used the distance between the two cities and trigonometry to estimate the Earth's circumference to within a few percentage points of the actual value.

Scientists determine the smells of objects in outer space

Using spectrographic techniques, scientists determine the chemical composition of planetary atmospheres, comets, and other objects in space. Combining these chemicals in labs on Earth has revealed locations in space that smell like nail polish remover, rotten fish, and urine.

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

The Deep Space Network keeps NASA linked to spacecraft billions of miles away

NASA's DSN is a global system of giant radio antennas that receive data from faraway spacecraft like Voyager 1 and the James Webb Space Telescope. It is sensitive enough to detect a signal as weak as a single light bulb from billions of miles away.

Differences in seismic wave speeds let scientists determine an earthquake’s location

Because primary waves are faster than secondary waves, seismic stations will detect longer gaps between these waves’ arrivals the farther an earthquake is. Calculating the distance to the earthquake from three stations allows its origin to be triangulated.

Gravity Probe B verified that rotating objects drag spacetime

The experiment involved attaching four freely floating gyroscopes to a telescope aimed at a distant star for a year. The observed angular shift of the gyroscopes as a result of Earth's rotation pulling on spacetime was approximately 0.0000012 degrees from the amount predicted by general relativity.

Even in an infinite universe, its limited age prevents a sky full of starlight

Olbers' paradox asks why the sky would ever appear dark if the universe is full of stars in all directions emitting light everywhere. Light from the farthest stars requires more time to reach our skies than the universe's age.

Since 2017, Virgo has helped LIGO localize astronomical phenomena

The detector near Pisa, Italy, coordinates its experimental runs with those in Hanford, Washington, and Livingston, Louisiana. Scientists can triangulate the locations of celestial events that generate gravitational waves using signal arrival times, just as earthquake locations can be determined from measurements at three seismic stations.

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

Climate data is monitored globally using tools from satellites to backyard gauges

Scientists use satellites, balloons, ocean buoys, and land-based instruments to track climate variables like temperature, precipitation, and wind. These tools gather data from deep ocean waters to the upper atmosphere.

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

The Astronomical Congress designated 88 groups of stars as official constellations

This 1928 decision helped distinguish important groups of stars used in navigation, calendars, and mythological storytelling from miscellaneous collections of stars called asterisms. The Big Dipper is a famous asterism in the constellation Ursa Major.

Scientists quantify how far from the poles auroras will be visible using the G-scale

The Geomagnetic Storm scale indicates the expected severity of the deformation of Earth's magnetic field based on the amount of energy injected by the solar wind. Solar activity is monitored using various satellites to forecast these storms, which can also be used to anticipate damage and disruption to power systems, radio communications, and satellite navigation.

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

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

Visualize the path of every solar eclipse from 1900 to 2099 and see what each looks like when observed from different locations on Earth.

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.

Stanford built a Google Maps for the Roman Empire, revealing how much it cost to travel in the ancient world

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Before humans, the Soviet Union and the United States sent animals—including apes, dogs, and cats—to space during the Space Race.

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.

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

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.

Hedge funds, the private investment firms that trade a wide swath of financial assets, make money by imposing steep fees on investors and from the fund's investment performance.

The term 'algorithm' originated from the Latinized name of al-Khwārizmī, a 9th-century mathematician whose works introduced Arabic numerals and the decimal-based numeral system to Europe and whose treatise 'Al-Jabr' gave algebra its name.

The first steps to rebuilding your credit score include getting to know exactly what's on your credit report and figuring out how far you are from the '700 club,' or 'good score' range.

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.

As of 2025, the most cited papers in science include a review of graphene, methods to improve image recognition, streamlining electron density calculations, and optimizing protein studies.

When you complete a CAPTCHA on a website to prove you are human, you may be unknowingly training algorithms for self-driving cars, whose systems require training data to help identify crosswalks, bicycles, and other outdoor objects.

Watch how deep-sea mining equipment collects and processes polymetallic nodules—metal-rich, potato-shaped rocks—from the ocean floor and creates environmentally damaging plumes of sediments.

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

In its famous catalog, Sears sold $600 DIY house kits from 1908 through the 1940s, resulting in an estimated 100,000 'Sears and Roebuck homes.'

Doctors differentiate between a phobia and fear by asking patients whether their fear interferes with their day-to-day activities.