Planet Profiles: Earth — What Makes Our Home Planet Unique?

Earth is the only world in the Universe known to support life.

It is a planet of deep oceans, moving continents, changing weather and extraordinary biological diversity. Liquid water flows across its surface, oxygen fills its atmosphere and a powerful magnetic field helps shield it from charged particles arriving from the Sun.

From the ground, Earth can feel impossibly vast. Seen from space, however, it becomes a small blue world surrounded by darkness—a fragile planet shared by every person, animal and plant we know.

Earth is not the largest, hottest or fastest planet in the Solar System. What makes it remarkable is the combination of conditions that has allowed life to emerge, survive and evolve for billions of years.

In this instalment of our Planet Profiles series, we explore how Earth formed, what lies beneath its surface and why its oceans, atmosphere, Moon and magnetic field are so important. We will also look at the ways astronomers can observe our home planet, from watching aurorae and satellites to photographing the atmosphere and seeing Earth’s reflected light on the Moon.

Earth at a Glance

• Planet type: Rocky terrestrial planet

• Position from the Sun: Third

• Average distance from the Sun: Approximately 150 million kilometres

• Diameter: Approximately 12,756 kilometres at the equator

• Age: Approximately 4.54 billion years

• Length of one year: Approximately 365.25 days

• Length of one rotation: Approximately 23 hours and 56 minutes

• Length of one solar day: 24 hours

• Number of moons: One

• Ring system: None

• Surface gravity: Approximately 9.8 metres per second squared

• Surface covered by water: Approximately 71%

• Average surface temperature: Approximately 15°C

• Atmosphere: Mainly nitrogen and oxygen

• Known to support life: Yes

• Visible without a telescope: You are standing on it

Why Is Earth Called the Blue Planet?

When viewed from space, Earth appears predominantly blue.

This is because oceans cover approximately 71% of its surface. Sunlight interacting with the water and atmosphere gives our planet its familiar blue appearance, while clouds form bright white patterns above the surface.

From orbit or deep space, Earth displays:

• Deep blue oceans

• White clouds and polar ice

• Green and brown continents

• Yellow and red desert regions

• Changing weather systems

• A thin blue atmospheric boundary

• Seasonal changes across the land and ice

The atmosphere looks thick and substantial from the ground, but images taken from space reveal it as an extremely thin layer surrounding the planet.

Almost all human activity, weather and known life exists within this narrow region between Earth’s solid surface and the emptiness of space.

How Did Earth Form?

Earth formed approximately 4.54 billion years ago from material surrounding the young Sun.

Dust, rock and metal within the early Solar System collided and gradually accumulated. Small particles became larger bodies, and repeated collisions eventually produced the young terrestrial planets.

Early Earth was very different from the world we recognise today. It was intensely hot, frequently struck by asteroids and other bodies, and experienced widespread volcanic activity.

As the young planet developed:

• Heavy materials such as iron and nickel sank towards the centre

• Lighter rocky materials formed the mantle and crust

• Volcanic gases contributed to the early atmosphere

• Water accumulated at the surface

• The crust cooled and became more stable

• Continents and oceans began to develop

• The first known life eventually appeared

Earth has continued changing ever since. Its continents move, mountains rise and erode, oceans open and close, species evolve and the composition of the atmosphere changes over geological time.

What Is Inside Earth?

Earth is composed of several main layers.

Although humans have drilled only a short distance into the crust, scientists can study the planet’s interior by analysing earthquakes, gravity, magnetism and the behaviour of rocks under extreme pressure.

The crust

The crust is Earth’s thin outermost layer.

There are two main types:

• Continental crust, which forms the continents and is generally thicker

• Oceanic crust, which lies beneath the oceans and is generally thinner and denser

Compared with the size of the entire planet, the crust is extremely thin—rather like the skin on an apple.

The mantle

Beneath the crust lies the mantle, which extends to a depth of approximately 2,900 kilometres.

The mantle is composed mainly of hot rock. Although mostly solid, some regions can flow extremely slowly over geological timescales.

Movement within the mantle helps drive plate tectonics, allowing sections of Earth’s crust to move across the planet’s surface.

The outer core

Earth’s outer core consists mainly of liquid iron and nickel.

Movement within this electrically conductive material helps generate the planet’s magnetic field. This process is known as the geodynamo.

The inner core

At the centre of Earth is a solid inner core made primarily of iron and nickel.

Temperatures are thought to approach those found at the surface of the Sun, but the enormous pressure prevents the inner core from melting.

Earth’s interior is still gradually losing heat left over from its formation, while radioactive elements within the planet also produce heat as they decay.

Why Do Earth’s Continents Move?

Earth’s outer shell is divided into large sections called tectonic plates.

These plates move slowly across the softer material beneath them, normally at rates comparable to the growth of fingernails. Over millions of years, however, even this slow movement can transform the planet.

Where plates interact, they can:

• Collide and build mountain ranges

• Move apart and create new oceanic crust

• Slide alongside one another

• Force one plate beneath another

• Produce earthquakes

• Create chains of volcanoes

• Open and close oceans

The continents have not always occupied their current positions.

At different points in Earth’s history, they have joined together into enormous supercontinents and later separated. The most recent major supercontinent, Pangaea, began breaking apart roughly 200 million years ago.

Plate tectonics continuously reshapes Earth’s surface and plays an important part in the long-term cycling of carbon, water and minerals.

Why Does Earth Have So Much Water?

Earth is the only planet in the Solar System known to have stable bodies of liquid water covering much of its surface.

Water is found in:

• Oceans

• Rivers and lakes

• Glaciers and ice sheets

• Underground reservoirs

• Soil

• The atmosphere

• Living organisms

• Minerals within Earth’s interior

The exact origin of Earth’s water is still being investigated.

Some water may have been present in the material from which Earth formed. Additional water may have been released through volcanic activity or delivered by water-rich asteroids during the planet’s early history.

Earth lies at a distance from the Sun where temperatures allow water to exist naturally as solid ice, liquid water and water vapour.

Water continuously moves between the oceans, land and atmosphere through the water cycle. Evaporation, condensation, rainfall, snowfall, freezing, melting and underground movement connect environments across the planet.

Liquid water is essential to every form of life currently known.

What Is Earth’s Atmosphere Made Of?

Earth’s atmosphere is composed primarily of:

• Approximately 78% nitrogen

• Approximately 21% oxygen

• Almost 1% argon

• Small amounts of carbon dioxide

• Variable amounts of water vapour

• Traces of neon, helium, methane and other gases

These gases are not distributed through an atmosphere with a clear upper edge. Instead, the air becomes progressively thinner with increasing altitude.

Earth’s atmosphere is commonly divided into several layers.

The troposphere

The troposphere is the lowest layer and contains most of the atmosphere’s mass.

Almost all familiar weather—including clouds, rain, snow and storms—occurs here.

The stratosphere

The stratosphere contains the ozone layer, which absorbs much of the Sun’s harmful ultraviolet radiation.

Commercial aircraft may fly near the lower part of this region because the air can be more stable than in the troposphere below.

The mesosphere

Many meteors become visible in the mesosphere as they heat the surrounding atmosphere and break apart.

The thermosphere

The thermosphere contains extremely thin air but can reach high temperatures as it absorbs energetic solar radiation.

Aurorae occur within regions of the upper atmosphere, including the thermosphere.

The exosphere

The exosphere is the outermost region, where particles can travel enormous distances without colliding and some escape into space.

Why Is Earth’s Atmosphere So Important?

Earth’s atmosphere performs several essential roles.

It:

• Provides gases used by living organisms

• Maintains enough pressure for liquid water to exist

• Distributes heat around the planet

• Produces weather and drives the water cycle

• Absorbs harmful ultraviolet radiation

• Burns up many small objects entering from space

• Helps regulate surface temperature

• Connects the oceans, land and living systems

Without its atmosphere, Earth would experience much more dramatic temperature differences between day and night.

The natural greenhouse effect also keeps the planet considerably warmer than it would otherwise be. Gases including water vapour, carbon dioxide and methane absorb some of the heat radiated from Earth’s surface.

This natural effect is necessary for life as we know it. However, increasing the concentration of greenhouse gases changes Earth’s energy balance and causes the global climate to warm.

Why Does Earth Have Seasons?

Earth’s seasons are caused by the tilt of its rotational axis—not by large changes in its distance from the Sun.

The planet’s axis is tilted by approximately 23.4 degrees relative to the plane of its orbit.

As Earth travels around the Sun, each hemisphere alternately tilts towards and away from it.

When the Northern Hemisphere is tilted towards the Sun:

• The Sun appears higher in the sky

• Daylight lasts longer

• Sunlight strikes the surface more directly

• The Northern Hemisphere experiences summer

• The Southern Hemisphere experiences winter

Six months later, the situation is reversed.

During spring and autumn, neither hemisphere is tilted strongly towards the Sun, producing the equinoxes.

Earth’s orbit is slightly elliptical, but the resulting change in distance is not the main cause of the seasons. In fact, Earth reaches its closest point to the Sun during the Northern Hemisphere’s winter.

How Long Is a Day on Earth?

Earth takes approximately 23 hours and 56 minutes to rotate once relative to the distant stars. This is known as a sidereal day.

A solar day—the average time from one midday to the next—is approximately 24 hours.

The difference occurs because Earth moves along its orbit while rotating. It must turn slightly farther for the Sun to return to the same position in the sky.

Earth’s rotation is gradually slowing, largely because of tidal interactions with the Moon. Far in the past, days were shorter than they are now.

Atomic clocks can measure extremely small variations in the length of a day caused by changes in Earth’s atmosphere, oceans, ice and interior.

Why Is a Year 365 Days Long?

Earth takes approximately 365.25 days to complete one orbit around the Sun.

Our calendar normally contains 365 days, so an additional day is added during most leap years to keep the calendar aligned with the seasons.

Without leap years, calendar dates would gradually drift relative to Earth’s position in its orbit.

Earth travels around the Sun at an average speed of almost 30 kilometres per second. At the same time, the Sun and the entire Solar System are moving through the Milky Way.

Even while you appear to be standing still, you are travelling through space at extraordinary speed.

What Is Earth’s Magnetic Field?

Earth behaves rather like a giant magnet.

Its magnetic field is generated mainly by the movement of electrically conductive liquid iron within the outer core.

The field extends far into space and creates a region called the magnetosphere.

This helps deflect many charged particles carried towards Earth by the solar wind. Some particles are channelled towards the polar regions, where their interaction with gases in the upper atmosphere can produce aurorae.

Earth’s magnetic field is not perfectly stable.

Its strength and direction change over time, and the magnetic poles move. Geological evidence shows that the north and south magnetic poles have reversed many times during Earth’s history.

A magnetic reversal does not mean the planet physically turns over. It means the direction of the magnetic field changes.

What Causes the Northern Lights?

The northern lights, or aurora borealis, occur when charged particles associated with the Sun interact with Earth’s magnetic field and upper atmosphere.

Energetic particles collide with atoms and molecules high above the surface. These interactions release light in different colours.

Common auroral colours include:

• Green, usually produced by oxygen

• Red, also associated with oxygen at greater altitudes

• Blue or violet, commonly associated with nitrogen

• Pink, which can result from a mixture of emissions

In the Southern Hemisphere, the same phenomenon is known as the aurora australis.

Aurorae are normally concentrated around the polar regions, but strong solar activity can make them visible much farther south. During a major geomagnetic storm, observers across Wales and other parts of the UK may see auroral displays.

A camera can often detect colour and structure that appears faint or grey to the unaided eye.

Why Is Earth Suitable for Life?

Earth possesses several conditions that have helped life survive and develop.

These include:

• Long-lasting liquid water

• A source of energy from the Sun

• A protective atmosphere

• Essential chemical elements

• A relatively stable climate over long timescales

• Active geological cycles

• A magnetic field

• A large Moon that helps stabilise Earth’s axial tilt

• A suitable distance from the Sun

• Sufficient gravity to retain an atmosphere

No single factor explains Earth’s habitability.

The oceans, atmosphere, rocks, living organisms, magnetic field and orbit all interact as parts of a complex planetary system.

Earth is located within the Sun’s habitable zone, where temperatures can allow liquid water to exist on a planet’s surface under suitable atmospheric conditions. Being within this zone does not guarantee life, however. Venus and Mars demonstrate how differently rocky planets can develop.

When Did Life Begin on Earth?

Life appeared relatively early in Earth’s history, although its exact origin remains uncertain.

Evidence indicates that simple life existed at least 3.5 billion years ago, and potentially earlier.

For much of Earth’s history, life consisted entirely of microscopic organisms. Complex multicellular organisms appeared much later, followed by an extraordinary diversification of plants and animals.

Photosynthetic microorganisms played an especially important role by releasing oxygen. Over immense periods, this changed the composition of the atmosphere and made oxygen-dependent life possible.

Humans occupy only a tiny portion of Earth’s history.

If the planet’s entire existence were compressed into a single 24-hour day, modern humans would appear only during the final seconds before midnight.

Is Earth Perfectly Round?

Earth is almost spherical, but it is not a perfect ball.

Its rotation causes the planet to bulge slightly at the equator and flatten at the poles. This shape is described as an oblate spheroid.

Earth’s equatorial diameter is therefore slightly greater than its polar diameter.

The planet’s shape is also affected by:

• Mountains and ocean trenches

• Differences in rock density

• Tides

• Ice sheets

• Atmospheric and ocean movement

• Variations in gravity

A more precise representation of Earth based on its gravitational field is known as the geoid.

The differences are far too small to make Earth look noticeably distorted when seen from space. It still appears as a nearly perfect sphere.

What Are Earth’s Highest and Deepest Places?

Earth’s surface contains enormous differences in elevation.

Mount Everest has the highest summit above mean sea level, reaching approximately 8,849 metres.

However, other measurements produce different answers:

• Mauna Kea is taller than Everest when measured from its base on the ocean floor to its summit.

• Chimborazo in Ecuador has the summit farthest from Earth’s centre because of the planet’s equatorial bulge.

The deepest known part of the ocean is the Challenger Deep within the Mariana Trench, reaching nearly 11 kilometres below sea level.

Despite these enormous landscapes, they are very small compared with Earth’s overall diameter.

Earth’s Moon

Earth has one permanent natural satellite: the Moon.

It orbits at an average distance of approximately 384,400 kilometres and is the fifth-largest moon in the Solar System.

The leading explanation for its formation is that a large body struck the young Earth billions of years ago. Material thrown into orbit eventually combined to form the Moon.

The Moon affects Earth in several important ways.

It:

• Produces most of the planet’s ocean tides

• Helps stabilise Earth’s axial tilt

• Gradually slows Earth’s rotation

• Illuminates the night sky

• Creates solar and lunar eclipses

• Provides a record of the early Solar System

• Has influenced human culture, calendars and exploration

The Moon is gradually moving away from Earth by a few centimetres each year.

Explore our detailed guides to the Moon, lunar phases and how to choose a telescope for lunar observation to learn more about our nearest celestial neighbour.

Why Do We Always See the Same Side of the Moon?

The Moon rotates once on its axis in the same amount of time that it takes to orbit Earth.

This is called synchronous rotation or tidal locking.

As a result, nearly the same lunar hemisphere always faces us. This is known as the near side.

The opposite hemisphere is called the far side—not the dark side. It receives just as much sunlight as the near side over the course of a lunar month.

Small apparent rocking motions called libration allow observers on Earth to see approximately 59% of the lunar surface over time.

Earthshine: Seeing Earth’s Light on the Moon

Although we cannot step away from Earth to view it directly, we can see its reflected light illuminating the Moon.

Shortly before or after a new Moon, the sunlit crescent may be accompanied by a faint glow across the remainder of the lunar disc.

This phenomenon is called earthshine.

Sunlight reflects from Earth’s clouds, oceans and land, travels to the Moon and then reflects back towards us. You are effectively seeing moonlight created by light that has already bounced from Earth.

Earthshine is often easiest to see:

• A few evenings after new Moon

• A few mornings before new Moon

• During clear twilight

• When the lunar crescent is thin

• Through binoculars or at low telescopic magnification

It is a beautiful reminder that Earth would appear as a bright, changing planet in the lunar sky.

Browse our astronomy binoculars for portable instruments suited to observing the Moon, earthshine and wide areas of the night sky.

What Would Earth Look Like From the Moon?

From the near side of the Moon, Earth would appear nearly four times wider than the Moon appears in our sky.

It would display phases opposite to those of the Moon.

When observers on Earth see a thin lunar crescent, someone on the Moon’s near side would see an almost fully illuminated Earth. When we see a full Moon, the Earth would appear close to its new phase.

Earth would also appear in almost the same region of the lunar sky because the same side of the Moon continually faces us.

It would be a dynamic sight, showing:

• Moving cloud systems

• Blue oceans

• Continents

• Polar ice

• Changing weather

• City lights on the night side

• A constantly shifting boundary between day and night

Unlike the visually unchanging lunar landscape, Earth would appear alive with movement.

Seeing Earth From Space

Only a relatively small number of people have seen the whole Earth directly from space.

Early satellite images transformed our understanding of weather and the planet’s interconnected systems. Human spaceflight then gave us some of the most influential photographs ever taken.

Earthrise

During the Apollo 8 mission in 1968, astronauts orbiting the Moon photographed Earth rising above the lunar horizon.

The image showed a colourful living world suspended above a barren grey landscape. It became one of the most recognisable photographs in history.

The Blue Marble

The Apollo 17 crew photographed a fully illuminated Earth in 1972 while travelling towards the Moon.

The resulting image, commonly known as The Blue Marble, revealed the planet as a complete world surrounded by darkness.

The Pale Blue Dot

In 1990, NASA’s Voyager 1 spacecraft photographed Earth from approximately six billion kilometres away.

Our entire planet occupied only a tiny fraction of a pixel—a faint point of light within a beam of scattered sunlight.

These images changed how many people understood Earth: not as an unlimited landscape, but as a small and isolated world.

How Do We Study Earth From Space?

Earth is observed continuously by satellites carrying a wide range of instruments.

They can measure and monitor:

• Clouds and rainfall

• Sea-surface temperature

• Ocean currents

• Atmospheric gases

• Air pollution

• Forests and vegetation

• Wildfires

• Ice sheets and glaciers

• Sea level

• Soil moisture

• Land movement

• Volcanoes

• Storms

• Changes in gravity

• Earth’s magnetic field

Some satellites use ordinary visible light. Others observe infrared, microwave, ultraviolet or radar wavelengths that reveal information human eyes cannot see.

Radar instruments can collect useful data through clouds and during darkness, while spectrometers can identify substances by the wavelengths of light they absorb or emit.

Earth-observation satellites support weather forecasting, environmental research, agriculture, navigation, disaster response and climate monitoring.

Important Earth-Observing Missions

Earth is the most intensively studied planet in the Solar System.

Landsat

The joint NASA and US Geological Survey Landsat programme has collected images of Earth’s land surface since 1972.

Its long record allows researchers to study urban growth, agriculture, forests, coastlines, water resources, wildfires and environmental change over decades.

Copernicus Sentinel Missions

Europe’s Copernicus Sentinel satellites monitor Earth using radar, visible-light cameras, ocean instruments and atmospheric sensors.

Their data supports research and practical services involving:

• Land and vegetation

• Oceans

• Sea ice

• Atmospheric composition

• Weather

• Natural disasters

• Climate change

EarthCARE

The European-Japanese EarthCARE mission studies clouds, aerosols and radiation.

These measurements help scientists investigate how clouds and airborne particles affect the amount of energy entering and leaving Earth’s climate system.

Biomass

The European Space Agency’s Biomass mission launched in 2025.

It uses a specialised radar capable of probing forest canopies to measure woody material such as trunks, branches and stems. This helps researchers estimate how much carbon is stored within forests and how those stores are changing.

DSCOVR

The Deep Space Climate Observatory, or DSCOVR, observes Earth from a point approximately 1.5 million kilometres towards the Sun.

Its EPIC camera records the fully illuminated face of Earth, capturing changing clouds, continents, oceans and atmospheric conditions.

Can You Observe Earth With a Telescope?

You cannot view Earth as a complete planet while standing on its surface, but a telescope can reveal many features within our atmosphere and near-Earth environment.

Possible targets include:

• The Moon illuminated by earthshine

• Aurorae

• Artificial satellites

• The International Space Station

• High-altitude clouds

• Atmospheric optical effects

• Distant landscapes

• Birds and wildlife

• The changing colours of twilight

Astronomical telescopes are not always the most convenient instruments for terrestrial observation because many designs produce an inverted or mirrored image.

A spotting scope or binoculars may be more practical for viewing landscapes, coastlines, wildlife and weather systems.

Explore our collection of binoculars and spotting scopes and accessories for daytime observation.

Observing Artificial Satellites

Thousands of active satellites and pieces of space hardware orbit Earth.

Many can be seen with the naked eye because they reflect sunlight. They often appear as steady points moving across the sky without the flashing navigation lights associated with aircraft.

Satellite visibility depends on:

• The observer’s location

• The satellite’s orbit

• The time of night

• The angle of sunlight

• Cloud cover

• The satellite’s size and orientation

Satellites are often easiest to see shortly after sunset or before sunrise, when the observer is in darkness but objects high above Earth remain illuminated by the Sun.

An astronomy app or satellite-tracking website can provide current pass times and directions.

Can You See the International Space Station?

Yes. During a favourable pass, the International Space Station can become one of the brightest objects in the night sky.

It normally appears as a brilliant point moving smoothly and rapidly from one part of the sky to another. A complete pass may last only a few minutes.

The ISS does not display flashing navigation lights. It may fade suddenly if it enters Earth’s shadow.

Through a telescope, it is possible to resolve the station’s general shape and solar panels, but tracking it manually is extremely challenging.

The safest and easiest introduction is to observe it with the naked eye or through low-magnification binoculars after checking an accurate pass prediction.

Never follow a satellite with optical equipment if its path takes it close to the Sun.

Observing Aurorae From the UK

Aurorae are sometimes visible from the UK, particularly from Scotland, northern England, Northern Ireland and areas with an unobstructed northern horizon.

Strong geomagnetic storms can bring displays much farther south, including Wales and southern England.

To improve your chances:

Check an aurora forecast

Monitor current space-weather information and alerts. Look for increased geomagnetic activity and reports from observers farther north.

Find a dark northern horizon

Choose a location away from direct streetlights with a clear view towards the north.

A beach, hilltop, rural field or elevated viewpoint can work well.

Allow your eyes to adapt

Faint aurorae may initially resemble pale cloud or a colourless glow. Give your eyes time to adjust to the darkness.

Use a camera

Modern cameras and smartphones can detect colours that are difficult to see with the naked eye.

A short exposure may reveal green, pink or red structures that appeared grey visually.

Watch for movement

Auroral arcs, rays and curtains may shift or brighten over a period of minutes. Continue observing even if the first signs appear faint.

Atmospheric Phenomena to Observe

Earth’s atmosphere creates many beautiful effects that can be studied without travelling far from home.

These include:

• Rainbows

• Halos around the Sun or Moon

• Sundogs

• Light pillars

• Crepuscular rays

• Glories

• Iridescent clouds

• Noctilucent clouds

• The green flash

• Atmospheric refraction

• Mirages

• Twilight arches

• Lunar coronas

Some of these phenomena are produced by water droplets, while others involve ice crystals, dust, atmospheric layers or the bending and scattering of light.

Solar safety warning: Never look directly at the Sun through binoculars, a telescope, spotting scope or camera lens unless properly certified solar-observing equipment is fitted and being used correctly. Ordinary sunglasses do not provide adequate protection.

Our guide to seeing and atmospheric conditions explains how Earth’s moving atmosphere also affects the sharpness of astronomical observations.

Can You See Earth’s Shadow?

Yes. Earth’s shadow can be observed in two different ways.

During a lunar eclipse

A lunar eclipse occurs when the Moon passes through Earth’s shadow.

As it enters the darkest region, the Moon may turn red or copper because sunlight passing through Earth’s atmosphere is bent into the shadow. Blue light is scattered more strongly, while red and orange wavelengths are more likely to reach the lunar surface.

In a sense, the red colour contains the light of every sunrise and sunset occurring around Earth’s edge at that moment.

After sunset or before sunrise

On a clear evening, look towards the east shortly after sunset. A dark blue-grey band may rise above the horizon beneath a pink region known as the Belt of Venus.

The dark band is Earth’s shadow extending through the atmosphere.

Before sunrise, the same effect may be seen in the western sky.

Can You Photograph Earth?

Yes—Earth is the most accessible planetary photography subject of all.

You can photograph its landscapes, atmosphere, weather, oceans, wildlife and relationship with the night sky.

Landscape astrophotography

Combining the night sky with a recognisable landscape creates a sense of place and scale.

Possible subjects include:

• The Milky Way above a mountain

• Star trails around an old building

• The Moon rising over the sea

• Venus above a twilight horizon

• A meteor shower over the countryside

• Aurorae above a Welsh landscape

• Earth’s shadow after sunset

Photographing weather

Cloud formations, lightning, storms, fog and rainbows reveal the dynamic behaviour of Earth’s atmosphere.

Remain aware of weather hazards and never place yourself in an exposed location during lightning, strong winds or dangerous coastal conditions.

Photographing earthshine

A telephoto lens or telescope can capture the bright lunar crescent together with the softly illuminated night side.

Because the crescent and earthshine differ greatly in brightness, separate exposures or careful editing may be needed to preserve detail in both.

Photographing satellites

A long exposure can record satellites as straight trails crossing the stars.

The ISS can appear as a bright line spanning a large part of the frame. Accurate pass predictions make it possible to plan compositions involving landmarks or landscapes.

Photographing through a telescope

A planetary or astronomy camera can be used to record:

• The Moon

• Lunar eclipses

• Earthshine

• The ISS

• High-altitude atmospheric events

• Transits of the ISS across the Moon or Sun

Solar transit photography requires specialist equipment, precise planning and strict safety precautions. It should not be attempted without a properly fitted, certified solar filter.

Explore our astrophotography and imaging collection for cameras, adapters and accessories.

Can Earth Be Seen From Another Planet?

In principle, Earth can be seen from other planets as a bright point of light.

From Mars, Earth would appear as an inner planet that remains relatively close to the Sun, rather as Venus appears from Earth. Powerful cameras aboard spacecraft on or around Mars have photographed Earth and the Moon together.

From much farther away, Earth becomes progressively fainter.

To an observer in another planetary system, Earth would be almost impossible to separate from the glare of the Sun without extremely advanced instruments.

However, astronomers might infer its presence by detecting:

• Its gravitational effect on the Sun

• A small reduction in sunlight as it passes in front of the Sun

• The composition of its atmosphere

• Reflected light from oceans, clouds and continents

• Seasonal variations

• Possible chemical signs associated with life

These are similar to the techniques astronomers use to study planets orbiting other stars.

Is Earth the Only Habitable Planet?

Earth is the only planet currently known to support life.

That does not prove that life exists nowhere else.

Scientists are searching for potentially habitable environments:

• Beneath the surface of Mars

• Within the underground oceans of Europa

• In the ocean beneath Enceladus’s icy crust

• On distant planets orbiting other stars

• In other environments where water, energy and suitable chemistry may coexist

Thousands of exoplanets have been discovered, including rocky worlds and planets orbiting within their stars’ potential habitable zones.

However, being within a habitable zone does not mean a planet is inhabited—or even genuinely habitable. Its atmosphere, gravity, geological activity, radiation environment and history all matter.

Earth remains the only example available for studying a living planetary system.

Common Misconceptions About Earth

Earth is perfectly spherical

Earth is slightly wider at the equator than at the poles and has an irregular gravitational shape.

The seasons are caused by distance from the Sun

The seasons are mainly caused by Earth’s axial tilt. Earth is actually closest to the Sun during early January.

The atmosphere ends at a fixed height

It becomes progressively thinner and gradually merges with space.

The Moon creates every tide by itself

The Moon produces most of Earth’s tides, but the Sun also makes a significant contribution.

Water covers all of Earth evenly

The oceans dominate the surface, but freshwater represents only a small proportion of Earth’s total water.

The magnetic poles and geographic poles are identical

They are different. The magnetic poles move and do not sit exactly at the geographic poles.

Earth is stationary while we observe the sky

Earth rotates on its axis, travels around the Sun and moves with the Solar System through the Milky Way.

Why Earth Is Worth Studying

Earth is familiar, but it is not ordinary.

It is a geologically active ocean world with moving continents, a complex atmosphere, a protective magnetic field and an extraordinary variety of living organisms.

Studying Earth helps us understand:

• How rocky planets evolve

• What makes a world habitable

• How atmospheres regulate temperature

• How water moves through a planetary system

• How life changes a planet

• How climates respond to natural and human influences

• What signs of life might be detectable on distant worlds

Every other planet in the Solar System provides a point of comparison.

Venus shows how an Earth-sized world can develop a crushing atmosphere and runaway greenhouse conditions. Mars demonstrates how a planet can lose much of its atmosphere and surface water. Mercury reveals an airless world exposed directly to space.

Earth occupies a remarkable position among them—not simply because it supports us, but because its oceans, rocks, atmosphere and life have been interacting for billions of years.

Seeing Our Home Planet Differently

You do not need to travel into space to appreciate Earth as a planet.

Watch its shadow rise after sunset. Look for sunlight reflected from Earth onto the darkened Moon. Follow the International Space Station as it crosses the evening sky. Photograph an aurora, a lunar eclipse or the Milky Way above a familiar landscape.

Astronomy is often described as the study of distant objects, but it also changes the way we see the world beneath our feet.

Earth is our observatory, our spacecraft and our only known home.

Every telescope, spacecraft image and planetary discovery ultimately gives us another way to understand it.

Continue Exploring the Solar System

Return to our Planet Profiles: A Beginner’s Guide to Our Solar System hub to explore every world in our planetary neighbourhood.

Previous in the series: Planet Profiles: Venus — Earth’s Brilliant but Hostile Neighbour

Next in the series: Planet Profiles: Mars — The Red Planet and How to Observe It

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