In this image of the Sun, the areas of greatest intensity appear almost white, while the darker red areas indicate less intensity.

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The atmosphere is a gaseous envelope surrounding and protecting our planet from the intense radiation of the Sun and serves as a key interface between the terrestrial and ocean cycles.

Earth’s atmosphere is a thin veil of gas surrounding the planet. Although it only extends a few hundred kilometers above the surface, it contains a mixture of gases, such as oxygen and nitrogen, that are critical for life to exist. It distributes incoming solar radiation, protecting life from harmful ultraviolet radiation but also driving atmospheric circulation and weather. The atmosphere enables the greenhouse effect, which makes Earth more habitable. Human activity, however, is contributing more gases, many of which are negatively impacting the protective nature of this vital layer. NASA data provide measurements on weather phenomena as well as gases within the troposphere (the lowest layer of the atmosphere) and stratosphere (the layer above the troposphere) and their effect on air quality.


Auroras are a brilliant display of light in the night sky. The aurora borealis and aurora australis—also known as the northern and southern lights—occur mainly near Earth's poles. When the solar wind reaches Earth's magnetosphere, it can send charged particles trapped in Earth’s magnetic field raining down toward Earth's poles, driven by a powerful process called magnetic reconnection. 

Along the way, particles can collide with atoms and molecules in Earth's upper atmosphere, which provides the atoms with extra energy that they release as a burst of light. These interactions continue at lower and lower altitudes until all the excess energy is lost. Glowing auroras are the result of millions of individual particle collisions, lighting up Earth's magnetic field lines. Studying auroras offers insights on how our magnetosphere reacts to near-Earth space weather.


The biosphere encompasses all life on Earth and extends from root systems to mountaintops and all depths of the ocean. It is critical for maintaining species diversity, regulating climate, and providing numerous ecosystem functions.

The biosphere is made up of the parts of Earth where life exists. It extends from the deep ocean floor, to lush rainforests, and high mountaintops. This important sphere supports almost every aspect of human well-being and distinguishes Earth from other planets in our solar system.

NASA data have changed the way we study life on Earth. Remote sensing and field-based data from NASA and partner federal agencies provide opportunities for biological and ecological research and applications. They have been used to assess the health of forests, detect tree cover loss, and prevent the spread of invasive species. Data on vegetation health, primary productivity, evapotranspiration, forest structure, and ocean chlorophyll provide insight into the health and productivity of the biosphere. NASA data can also can be used to study the suitability of an environment for different species as well as species distribution within a habitat.

Climate Change

The term 'climate change' is sometimes used to refer to all forms of climatic inconsistency, but because the Earth's climate is never static, the term is more properly used to imply a significant change from one climatic condition to another. In some cases, 'climate change' has been used synonymously with the term, 'global warming'; scientists however, tend to use the term in the wider sense to also include natural changes in climate.

Co-evolution of Life/Earth

The dynamic causes, effects, and feedbacks between the biosphere and Earth’s other systems, whereby geoscience factors control the evolution of life, which in turn continuously alters Earth’s surface. Examples include how photosynthetic life altered the atmosphere through the production of oxygen, which in turn increased weathering rates and allowed for the evolution of animal life; how microbial life on land increased the formation of soil, which in turn allowed for the evolution of land plants; or how the evolution of corals created reefs that altered patterns of erosion and deposition along coastlines and provided habitats for the evolution of new life forms.


The rising of warm air and the sinking of cool air. Heat mixes and moves air. When a layer of air receives enough heat from the Earth's surface, it expands and moves upward. Colder, heavier air flows under it which is then warmed, expands, and rises. The warm rising air cools as it reaches higher, cooler regions of the atmosphere and begins to sink. Convection causes local breezes, winds, and thunderstorms.


The Sun's dynamic upper atmosphere is called the corona. It is filled with plasma, whose movements are governed by the tangle of magnetic fields surrounding the Sun. Temperatures in the corona can reach up to millions of degrees. The corona is the source of the solar wind as well as solar flares and coronal mass ejections – the energetic solar eruptions that create the strongest space weather. 

Coronal Mass Ejection

Coronal mass ejections, or CMEs, are large clouds of solar plasma and embedded magnetic fields released into space after a solar eruption. CMEs expand as they sweep through space, often measuring millions of miles across, and can collide with planetary magnetic fields. When directed at Earth, a CME can produce geomagnetic disturbances that ignite bright aurora, short-circuit satellites and power grids on Earth, or at their worst, even endanger astronauts in orbit.

Earth's Energy Budget

A quantitative description of the energy exchange for a physical or ecological system. The budget includes terms for radiation, conduction, convection, latent heat, and for sources and sinks of energy.


Any natural unit or entity including living and non-living parts that interact to produce a stable system through cyclic exchange of materials.

Electromagnetic Spectrum

The entire range of radiant energies or wave frequencies from the longest to the shortest wavelengths--the categorization of solar radiation. Satellite sensors collect this energy, but what the detectors capture is only a small portion of the entire electromagnetic spectrum. The spectrum usually is divided into seven sections: radio, microwave, infrared, visible, ultraviolet, x-ray, and gamma-ray radiation.


Electromagnetism is one of the fundamental forces of nature. Early on, electricity and magnetism were studied separately and regarded as separate phenomena.  Hans Christian Ørsted discovered that the two were related – electric currents give rise to magnetism.  Michael Faraday discovered the converse, that magnetism could induce electric currents, and James Clerk Maxwell put the whole thing together in a unified theory of electromagnetism.


Scientists define energy as the ability to do work. Modern civilization is possible because people have learned how to change energy from one form to another and then use it to do work. People use energy to walk and bicycle, to move cars along roads and boats through water, to cook food on stoves, to make ice in freezers, to light our homes and offices, to manufacture products, and to send astronauts into space. There are many forms of energy: heat, light, motion, electrical, chemical, gravitational.

Geomagnetic Storm

A geomagnetic storm is a major disturbance of Earth's magnetosphere that occurs when there is a very efficient exchange of energy from the solar wind into the space environment surrounding Earth. These storms result from variations in the solar wind that produces major changes in the currents, plasmas, and fields in Earth’s magnetosphere. The solar wind conditions that are effective for creating geomagnetic storms are sustained (for several to many hours) periods of high-speed solar wind, and most importantly, a southward directed solar wind magnetic field (opposite the direction of Earth’s field) at the dayside of the magnetosphere. This condition is effective for transferring energy from the solar wind into Earth’s magnetosphere.

Greenhouse Effect

The greenhouse effect is the way in which heat is trapped close to Earth's surface by “greenhouse gases.” These heat-trapping gases can be thought of as a blanket wrapped around Earth, keeping the planet toastier than it would be without them. 

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Habitable Zone

The definition of “habitable zone” is the distance from a star at which liquid water could exist on orbiting planets’ surfaces. Habitable zones are also known as Goldilocks’ zones, where conditions might be just right – neither too hot nor too cold – for life.


The Sun’s constantly outflowing material, the solar wind, inflates a bubble in space called the heliosphere. The heliosphere encloses all of the planets and is filled by the Sun’s plasma and magnetic field. In interstellar space outside the heliosphere, the interstellar medium and the galactic magnetic field are dominant. The heliosphere acts as a shield for our solar system, blocking many of the high-energy galactic cosmic rays from elsewhere in our galaxy. Of the spacecraft sent from Earth, only the twin Voyager spacecraft — traveling since 1977 — have been confirmed to have made it beyond the boundaries of the heliosphere. 

Interstellar Space

Interstellar space is often called the space between the stars, but more specifically, it’s the region between our Sun’s heliosphere and the astrospheres of other stars.

Our heliosphere is a vast bubble of plasma – a gas of charged particles – that spews out of the Sun. This outflow is known as the solar wind. The bubble surrounds the Sun and stretches beyond the planets. Both Voyager spacecraft had to travel more than 11 billion miles (17 billion kilometers) from the Sun in order to cross the edge of the heliosphere. This bubble is moving through interstellar space as the Sun orbits the center of the Milky Way galaxy. As our heliosphere plows through space, it creates a bow wave, like the wave formed by the bow of a ship.


The nucleus of an atom is surrounded by electrons that occupy shells, or orbitals of varying energy levels. The ground state of an electron, the energy level it normally occupies, is the state of lowest energy for that electron.There is also a maximum energy that each electron can have and still be part of its atom. Beyond that energy, the electron is no longer bound to the nucleus of the atom and it is considered to be ionized.


1. Form of radiant energy that acts upon the retina of the eye, optic nerve, etc., making sight possible. This energy is transmitted at a velocity of about 186,000 miles per second by wavelike or vibrational motion.

2. A form of radiant energy similar to this, but not acting on the normal retina, such as ultraviolet and infrared radiation.

Interplay between light rays and the atmosphere cause us to see the sky as blue, and can result in such phenomena as glows, halos, arcs, flashes, and streamers.

Lunar Eclipse

During a lunar eclipse, Earth comes between the Sun and the Moon, blocking the sunlight falling on the Moon.

There are two kinds of lunar eclipses: A total lunar eclipse occurs when the Moon and Sun are on opposite sides of Earth. A partial lunar eclipse happens when only part of Earth's shadow covers the Moon.

During some stages of a lunar eclipse, the Moon can appear reddish. This is because the only remaining sunlight reaching the Moon at that point is from around the edges of the Earth, as seen from the Moon's surface. From there, an observer during an eclipse would see all Earth's sunrises and sunsets at once.

Lunar Phases

Our Moon doesn't shine, it reflects. Just like daytime here on Earth, sunlight illuminates the Moon. We just can't always see it.

When sunlight hits off the Moon's far side — the side we can't see without from Earth the aid of a spacecraft — it is called a new Moon.

When sunlight reflects off the near side, we call it a full Moon.

The rest of the month we see parts of the daytime side of the Moon, or phases. These eight phases are, in order, new Moonwaxing crescentfirst quarterwaxing gibbousfull Moonwaning gibbousthird quarter and waning crescent. The cycle repeats once a month (every 29.5 days).

Magnetic Fields

Every magnet produces an invisible area of influence around itself. When things made of metal or other magnets come close to this region of space, they feel a pull or a push from the magnet. Scientists call these invisible influences FIELDS. You can make magnetic fields visible to the eye by using iron chips sprinkled on a piece of paper with a magnet underneath.

Magnetic Reconnection

When magnetic field lines become mixed, they can explosively snap and realign, flinging away nearby particles at high speeds in a process called magnetic reconnection. This process occurs across the universe, including on the Sun, near black holes, and around Earth. Particles launched by magnetic reconnection near Earth can travel down along magnetic field lines into the atmosphere, where they can spark auroras.


A magnetosphere is the region around a planet dominated by the planet's magnetic field. In our solar system, several planets, including Earth, and even one of Jupiter’s moons have magnetospheres. Magnetospheres of planets have a “teardrop” or ice cream cone shape, with a rounded, shorter end created as the Sun’s material pushes against the magnetic field and a long tail trailing away on the other side. Earth's magnetosphere has played a crucial role in our planet's habitability as it shields our home planet from solar and cosmic particle radiation, as well as erosion of the atmosphere by the solar wind.


The side of the magnetosphere facing away from the sun - the nightside - stretches out into an immense magnetotail, which fluctuates in length and can measure hundreds of Earth radii, far past the moon's orbit at 60 Earth radii.


We live in a world that is defined by three spatial dimensions and one time dimension. Objects move within this domain in two ways. An object translates, or changes location, from one point to another. And an object rotates, or changes its attitude. In general, the motion of any object involves both translation and rotation. The translations are in direct response to external forces. The rotations are in direct response to external torques or moments (twisting forces).

Topics from N-S

Newton's Law of Gravity

All bodies attract each other with what is called gravitational attraction. This applies to the largest stars as well as the smallest particles of matter.

The force of attraction between two small bodies (or between two spherical bodies of any size) is proportional to the product of their masses and inversely proportional to the square of the distance between their centers. In other words, the closer two bodies are to each other, the greater their mutual attraction. As a result, to stay in orbit, a satellite needs more speed in a low than a high orbit.

Kepler's three laws of planetary motion, which had been derived empirically by Johannes Kepler, were obtained with mathematical rigor as a consequence of Newton's law of universal gravitation in conjunction with his three laws of motion. See Kepler's three laws of motion.

Nuclear Fusion

Nuclear fusion is a process that produces energy when two nuclei join to form a heavier nucleus. “Scientists are interested in fusion, because it could generate enormous amounts of energy without creating long-lasting radioactive byproducts,” said Theresa Benyo, Ph.D., of NASA’s Glenn Research Center. “However, conventional fusion reactions are difficult to achieve and sustain because they rely on temperatures so extreme to overcome the strong electrostatic repulsion between positively charged nuclei that the process has been impractical.


Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar.


Plasma is a state of matter distinct from solids, liquids and gases. Though rare on Earth, plasma makes up over 99% of the observable (i.e., not dark) matter in the universe, including every star and much of the material between them. On Earth, plasma is found in fluorescent lights, torches used for metalworking, and lightning strikes.

Plasma forms when the atoms in a gas become ionized, meaning electrons separate from the atom and move around independently. This makes plasmas electrically charged and they can interact with external electric and magnetic fields.  They can also create their own electric and magnetic fields. Plasmas also undergo an explosive process called magnetic reconnection. Magnetic reconnection is a rapid transfer of magnetic energy into motion that powers solar flares and coronal mass ejections.


Energy transfer in the form of electromagnetic waves or particles that release energy when absorbed by an object.

Radio Blackout

Radio blackouts occur when the strong, sudden burst of x-rays from a solar flare hits Earth's atmosphere, jamming both high and low frequency radio signals. The X-rays disturb a layer of Earth's atmosphere known as the ionosphere, through which radio waves travel. The constant changes in the ionosphere change the paths of the radio waves as they move, thus degrading the information they carry. This affects both high and low frequency radio waves alike. The loss of low frequency radio communication causes GPS measurements to be off by feet to miles, and can also affect the applications that govern satellite positioning.


A time of year, caused by Earth’s tilt. A year on Earth is usually divided into four quarters, or seasons: spring, summer, autumn or fall, and winter.


Solar Cycle

Eleven-year cycle of sunspots and solar flares that affects other solar indexes such as the solar output of ultraviolet radiation and the solar wind. The Earth's magnetic field, temperature, and ozone levels are affected by this cycle.

Solar Eclipse

​Eclipses happen when one object in space passes through the shadow of another object in space. During a solar eclipse, the Moon passes between the Sun and Earth, blocking all or part of the Sun for the viewer.

Annular Solar Eclipse
An annular eclipse happens when the Moon is lined up between the Sun and Earth, but at its farthest point from Earth. Because the Moon is farther away from Earth than usual, it seems smaller. It does not block the entire view of the Sun. When it is in front of the Sun, the Moon will look like a dark disk on top of a larger, bright disk. This creates what looks like a ring around the Moon.

Total Solar Eclipse
For a total eclipse to take place, the Sun, Moon, and Earth must be
in a direct line. The people who see the total eclipse are in the center of the Moon’s shadow when it hits Earth. The sky will darken, as if it were twilight. Weather permitting, people in the path of a total solar eclipse can see the Sun’s corona, the outer atmosphere of the Sun. A total solar eclipse is the only type of solar eclipse where viewers can watch without their eclipse glasses – and they can only remove them when the Moon is completely blocking the Sun.

Hybrid Eclipse
Sometimes a solar eclipse can appear as an annular in some places and a total in others as the Moon’s shadow moves across Earth’s surface. This is known as a hybrid eclipse.

Partial Solar Eclipse
A partial eclipse happens when the Sun, Moon, and Earth are not
exactly lined up. Only a part of the Sun will appear to be covered.
During a total or annular solar eclipse, people outside the Moon’s
inner shadow see a partial solar eclipse. 

Solar Flare

Solar flares are energetic bursts of light and particles triggered by the release of magnetic energy on the Sun. Flares are by far the most powerful explosions in the solar system, with energy releases comparable to billions of hydrogen bombs. The energetic particles accelerated by flares travel nearly at the speed of light, and can travel the 93 million miles between the Sun and Earth in less than 20 minutes. Some solar flares have an associated coronal mass ejection.

Solar System

There are many planetary systems like ours in the universe, with planets orbiting a host star. Our planetary system is called “the solar system” because we use the word “solar” to describe things related to our star, after the Latin word for Sun, "solis." Our solar system consists of our star, the Sun, and everything bound to it by gravity – the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune; dwarf planets such as Pluto; dozens of moons; and millions of asteroids, comets, and meteoroids.

Solar Wind

The solar wind is a gusty stream of material that flows from the Sun in all directions, all the time, carrying the Sun’s magnetic field out into space.  While it is much less dense than wind on Earth, it is much faster, typically blowing at speeds of one to two million miles per hour. The solar wind is made of charged particles — electrons and ionized atoms — that interact with each other and the Sun’s magnetic field. The extent of the solar wind creates the heliosphere, the Sun’s region of influence within interstellar space.

Space Weather

Space weather refers to conditions in space produced by the Sun’s activity. The Sun affects the space around us through a constant stream of plasma known as the solar wind, with occasional bursts from solar flares and coronal mass ejections. These solar discharges carry their own magnetic field, so when they collide with Earth’s magnetic field, the two magnetic fields can repel or attract each other like two magnets. This repulsion and attraction creates geomagnetic disturbances. Space weather events produce the beautiful glow of the northern and southern lights, but they can also endanger astronauts, disrupt radio communications, and even cause large electrical blackouts.

Every planet in the solar system experiences its own space weather as the solar wind interacts with the planet’s own magnetic field (or lack thereof).


Spectroscopy is a complex art - but it can be very useful in helping scientists understand how an object like a black hole, neutron star, or active galaxy is producing light, how fast it is moving, and even what elements it is made of. A spectrum is simply a chart or a graph that shows the intensity of light being emitted over a range of energies. Spectra can be produced for any energy of light - from low-energy radio waves to very high-energy gamma-rays.

Stellar Evolution (Life Cycle of Stars)

A star is born, lives, and dies, much like everything else in nature. Using observations of stars in all phases of their lives, astronomers have constructed a lifecycle that all stars appear to go through. The fate and life of a star depends primarily on it's mass.



The closest star to Earth (149,599,000 km away on average). The sun dwarfs the other bodies in the solar system, representing approximately 99.86 percent of all the mass in the solar system. One hundred and nine Earths would be required to fit across the Sun's disk, its interior could hold over 1.3 million Earths.

The source of the Sun's energy is the nuclear reactions that occur in its core. There, at temperatures of 15 million degrees Celsius (27 million degrees Fahrenheit) hydrogen atom nuclei, called protons, are fused and become helium atom nuclei. The energy produced through fusion at the core moves outward, first in the form of electromagnetic radiation called photons. Next, energy moves upward in photon heated solar gas--this type of energy transport is called convection. Convective motions within the solar interior generate magnetic fields that emerge at the surface as sunspots and loops of hot gas called prominences. Most solar energy finally escapes from a thin layer of the Sun's atmosphere called the photosphere--the part of the Sun observable to the naked eye.

The sun appears to have been active for 4.6 billion years and has enough fuel for another 5 billion years or so. At the end of its life, the Sun will start to fuse helium into heavier elements and begin to swell up, ultimately growing so large that it will swallow Earth. After a billion years as a 'red giant,' it will suddenly collapse into a 'white dwarf.' It may take a trillion years to cool off completely.


Sun's Layers

Core: More than 27 million degrees Fahrenheit and 10 times denser than lead, the solar core is the very center of our Sun. Here, the intense pressure from surrounding layers compresses the center to a dense ball — about 172,000 miles across in diameter — where hydrogen atoms are squeezed together into helium, releasing energy and light in the process. This reaction, known as nuclear fusion, has powered our Sun for over 4 billion years and will continue for an estimated 5 billion more.

Radiative Zone: The radiative zone is the layer just outside the Sun’s core. This region varies in density, from denser than gold to less dense than water. The radiative zone gets its name from how light is transferred from the core below to the zone above. Here, the light is passed from atom to atom, instead of circulating as it does in the less dense convection zone.

Convection Zone: The convection zone is the outermost layer of the solar interior and makes up about 2/3 of the Sun’s volume. At the base of the convection zone, the temperature is about 3.5 million degrees Fahrenheit. The convection zone is much less dense than the radiation zone, with about the same density as the air 50 miles above Earth’s surface. The hot material there rises to the surface of the star, carrying, or convecting, heat with it.  Once the material cools by giving off sunlight, it sinks down, where it picks up more heat. The convective motions themselves are visible at the surface as features called granules and supergranules.

Photosphere: Often called the “surface” of the Sun, the photosphere is actually the first layer of the solar atmosphere – and it is far less dense than Earth’s air at sea level. About 250 miles thick and averaging about 10,000 degrees Fahrenheit, this layer emits the white light we can see with our eyes. (The Sun appears yellow from the surface of Earth because the blue light is scattered out by the particles in our atmosphere, which also makes the sky appear blue.)

Chromosphere: The chromosphere lies just atop the photosphere, about 1,050 miles thick on average.  The temperature in the chromosphere rises from about 10,000 degrees Fahrenheit to about 36,000 degrees Fahrenheit, hotter than the photosphere but nowhere near as hot as the Sun’s multi-million degree upper atmosphere, known as the corona. Named for the bright reddish color it gives off, the chromosphere is notoriously tricky to study, because it’s where the physical laws affecting the motion of solar material begin to change. In the lower chromosphere, solar material moves as a typical gas or fluid; in the upper chromosphere and above, magnetic forces dominate the motion.

Transition Region: The transition region is where the chromosphere becomes the corona, and the temperature rapidly rises from thousands to millions of degrees. Estimated to be about 60 miles thick, its exact height and position is not well defined. Instead, the “transition region” forms a kind of halo around the shifting, churning features of the chromosphere.

Corona: The Sun's dynamic upper atmosphere is called the corona. It is filled with plasma, whose movements are governed by the tangle of magnetic fields surrounding the Sun. Temperatures in the corona can reach up to millions of degrees. The corona is the source of the solar wind as well as solar flares and coronal mass ejections – the energetic solar eruptions that create the strongest space weather. 


Occasionally, dark spots freckle the face of the Sun. These are sunspots, cooler regions on the Sun’s visible surface caused by a concentration of magnetic field lines. Sunspots are the visible component of active regions, areas of intense and complex magnetic fields on the Sun that are the source of solar eruptions. Lasting from days to months, sunspots typically stretch 1,000 to 100,000 miles across. The number of sunspots goes up and down as the Sun goes through its natural 11-year cycle. Scientists use sunspots to help them track this cycle.


Topics from N-S

Thermal Energy

The heat source for our planet is the sun.  Thermal energy from the Sun (radiataion) is transferred through space and through the earth's atmosphere to the earth's surface. Since this energy warms the earth's surface and atmosphere, some of it is or becomes heat energy. There are three ways heat is transferred into and through the atmosphere: radiation, conduction, and convection.



A transit happens when one celestial body crosses in front of another from a specific point of view. Eclipses are a type of transit. On Earth, we most often see Mercury transit the Sun, or – even more rarely – Venus.  

Transits are also one of the primary ways scientists look for evidence of exoplanets, planets beyond our solar system. As exoplanets pass between their host star and Earth, the light we measure from the host star decreases slightly, giving scientists clues about the planet or planets that may be orbiting that star.


Van Allen Belts

Named for their discoverer, James Van Allen, these concentric, doughnut-shaped rings encircle Earth and are filled with high-energy particles trapped by Earth’s magnetic field to create the radiation belts. The particles – electrons and ions – gyrate, bounce, and drift through the region, sometimes shooting down into Earth's atmosphere, sometimes escaping out into space. The radiation belts swell and shrink during 1-3 day long geomagnetic storms as part of a much larger space weather system driven by energy and material that erupts off the Sun and fills the entire solar system. The Van Allen Belts are an important component of the Earth’s magnetosphere.