Why the edge of Earth's atmosphere varies depending on which property is considered

The informal boundary between the Earth and outer space lies within the atmosphere

Located approximately 100 kilometers (62.1 miles) above Earth's surface, the Kármán line serves as the approximate location where air density is too low to support aerodynamic lift to keep an aircraft airborne. Beyond this height, thrust is needed to propel objects through the air.

The importance of the mesosphere, the coldest part of Earth's atmosphere

Atmospheric gases are dense enough in this region to begin burning up debris traveling toward Earth's surface, producing meteor showers, or shooting stars. Although we normally associate decreasing temperatures with increasing altitude, temperatures increase beyond the mesosphere layer due to the absorption of high-energy ultraviolet radiation and X-rays.

The weight of Earth's atmosphere is equivalent to a 33-foot deep, global ocean

Because air is made up of gas molecules with mass, it is not weightless. On the planet's surface, we are effectively living in what is the equivalent of the bottom of an invisible ocean of these particles pressing against us, just as water molecules do when we are submerged.

Why Earth's atmosphere constantly loses the universe's lightest elements to space

The masses of hydrogen and helium are too small for these gases to be held by Earth's gravitational force, particularly when these atoms are given energy from collisions with high-speed particles from the sun. Although the planet loses a meter-wide balloon's worth of hydrogen every second, it will still take billions of years to exhaust the planet of this element.

The moon's little-known, incredibly thin atmosphere

Earth's colorless, lifeless moon is often portrayed as devoid of an atmosphere. However, this fascinating article describes the very thin layer of gases floating above the surface of our celestial neighbor, a layer so thin it's technically known as...

The edge of the Milky Way may be identified by its star-forming disk

Like Earth's atmosphere and its core, galaxies become more diffuse with increasing distance from their centers, making it hard to define where they end. However, one approach focuses on where gas concentrations are no longer dense enough to support measurable star formation.

How scientists study Earth's geocorona, the farthest portion of the planet's exosphere

Seen via ultraviolet radiation scattered by neutral hydrogen in the region, observations by the ESA/NASA Solar and Heliospheric Observatory indicate that the geocorona extends roughly 50 times Earth's diameter above its surface. At this distance, the geocorona extends beyond the Moon's orbit.

View the transparency of Earth's atmosphere and how it blocks most forms of light

The gases that make up Earth's atmosphere block most harmful forms of electromagnetic radiation from reaching the planet's surface, except for some ultraviolet light. Their transparency to radio waves means this form of light can reach Earth's surface, which is why most radio telescopes are ground-based rather than space-based.

Understanding why the thermosphere feels cold, despite exceeding 2,000 degrees Celsius

High-energy solar radiation can raise temperatures above 2,000 degrees Celsius (3,632 degrees Fahrenheit), but the air density in this layer is so low that there would be insufficient collisions between energized molecules and a person's skin to cause them to experience this warmth. Variations in the level of solar radiation reaching the layer cause it to swell and shrink.

Atmospheric greenhouse gases trap thermal energy and make Earth habitable

The moon and Earth are at the same distance from the sun, but the moon experiences large fluctuations in surface temperature because it lacks an atmosphere to insulate it. Gases such as water vapor, ozone, carbon dioxide, and methane can intercept about 90% of the infrared radiation emitted by Earth's surface.

View the internal structure of the sun and its puzzling surrounding atmosphere

From the stellar core to the surface, the sun's density decreases from more than 10 times that of lead to 0.00001% that of air, while temperatures drop from millions to thousands. Temperatures increase from the sun's surface to the outermost layer of its atmosphere—the corona—a phenomenon whose explanation is still under investigation.

The boiling temperature of water decreases with increasing elevation because the molecules need less energy to overcome the lower atmospheric pressure associated with thinner air.

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.

Explore Earth's atmosphere and what its layers contain in this interactive adventure

In this interactive, users can move from Earth's surface up through its atmosphere, exploring the natural phenomena found in each layer, including atmospheric rivers, auroras, and meteor showers. Artificial structures such as weather balloons and the International Space Station can also be found on the adventure.

Where you are located in a gravitational field affects how quickly you age

The closer something is to the center of a massive object, the greater the strength of the massive object's gravitational field as a result of space-time being depressed more severely. Time passes more slowly the deeper an object is in this gravitational depression, meaning objects in the universe naturally seek to age more slowly.

Tidally locked exoplanets experience extreme atmospheric temperatures

On worlds like WASP 76b, which orbits its host star approximately 3% the Earth-sun distance, temperatures on its day side can vaporize iron. Winds more than 14 times the speed of sound blow this material to its night side, where it condenses and falls as liquid metal.

Zooming out from Earth to the edge of space

For perspective on the universe's absolute massiveness, watch this four-minute video. Beginning at a facility in Germany, the "camera" pulls back revealing the surrounding countryside, Germany itself, Europe, the Earth, and so on. At one point stars form galaxies and galaxies, at a distance, become as seemingly "small" as the individual stars.

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.

The boiling temperature of water decreases with increasing elevation because the molecules need less energy to overcome the lower atmospheric pressure associated with thinner air.

Martian skies and sunsets resembled Earth's hundreds of millions of years ago

Evidence suggests that Mars has had a thicker atmosphere, which included greenhouse gases, and a magnetic field in its past, resembling Earth's current composition. After losing its magnetic field—the protection from solar wind—the atmosphere and its associated atmospheric phenomena gradually disappeared.

Understanding why suction cups rely on Earth's atmosphere to work

When pressed against a surface, air is squeezed out of a sealed volume, causing the internal pressure to drop below the surrounding atmospheric pressure, and this imbalance creates the "sticking." For this reason, astronauts do not use suction cups or related technologies to stay on spacecraft during spacewalks.

Why quantum mechanics causes disagreement on where the edge of an atom is located

The quantum model of the atom describes it as having a dense nucleus at its center, surrounded by electrons in probability clouds where they are most likely to be found. The fundamental uncertainty of these clouds has led to various methods and resulting measurements of the atomic radius. (Some readers may experience a paywall.)

The International Space Station is slowly falling due to atmospheric drag

To stay in orbit, the largest human-made object in space needs periodic rocket boosts to maintain its orbital speed and height. Its solar panels collect enough energy to power over 60 average US homes each year.

Who owns outer space?

More and more material ends up in Earth's orbit, posing threats to orbiting space stations and satellites. A 1960s treaty technically made space the common property of humankind, but with increasing chances of conflict in space, things can seem anarchic. This video breaks down the brewing tensions in space.

Orbital spaceflight requires reaching 23 times the speed of sound

After the spacecraft accelerates up to at least 17,500 miles per hour, space tourists can travel in elliptical orbits hundreds of miles above Earth for days or weeks at a time. Suborbital flights instead max out at about 2,200 miles per hour and travel only 50 to 70 miles above Earth's surface for a few minutes.

Explaining why the Earth wobbles

Astronomers going back to Hipparchus in the 2nd century BCE have noticed our planet has a distinct wobble. More recently, scientists have observed that the Earth is 26 miles wider at the equator than from pole to pole. The wobble results from our...

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 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.

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.

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.'

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

According to the physics of black holes, our 4D reality may be a hologram—a projection of information coded on a 2D surface on the edge of the universe.

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.

See the 25 of the best photos of auroras from around the world.

Volcanoes 'die' when their supply of magma runs out, if they are shifted away from their underlying magma reservoir, or if they get clogged by collapsing or their magma cooling back into rock.

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

Chaos theory—informally known as the butterfly effect—is the reason why weather forecasts are presented with probabilities rather than certainties.

Apollo astronauts left items in the moon's 'toss zone,' including golf balls, family photos, and bags of human waste, to make room for lunar rocks.

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

An investigation suggests a Scottish island became awash in forever chemicals via seafoam and seaspray—raising questions about what that means for the safety of other coastal areas.

The price of gas is a composite made up of several different factors, with the federal gas tax making up less than 20% of what drivers pay at the pump.

While El Niño moves warm Pacific Ocean waters east along the equator, La Niña moves them west, shifting where rainfall will become more common for months.

Double world record holder Hunter Ewen helped conquer his fear of balloons, called globophobia, by training to win Guinness World Record titles for balloon inflation.

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

The original copy of the Declaration of Independence is not a pristine document, and even features a smudged anonymous handprint in the bottom left corner.

See this overview of the firework rules across all 50 states, ranging from a complete ban on non-professional fireworks in Massachusetts to states with more lax rules like Indiana.

When a Paris department store hesitated to sell Estée Lauder's perfume, she 'accidentally' broke a bottle, causing the smell to spread throughout the store and shoppers to start asking to buy the scent.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

Iran's Revolutionary Guard Corps is independent of Iran's regular army and is one of the most powerful and influential military-political organizations in the Middle East.