Seeing Earth from space was a dream of humanity for a long time before it was possible. Our home planet, third from the sun and one of a group of four that make up the inner Solar System, was once difficult to envision as a sphere hanging in empty space. Although the birth of telescope-aided astronomy allowed us to see other planets for the first time, it was a stretch for us to imagine that we were living on a similar body, and to picture quite what we might see if we were able to view Earth from space.
With a diameter of approximately 8,000 miles, or 13,000 kilometres, Earth is the fifth largest planet in our solar system, and the largest of the rocky planets. Viewing Earth from space we can see that it's not a perfect sphere, because its rotations cause it to be slightly wider around the equator than it is from pole to pole. Nicknamed The Blue Planet as that is the most prominent colour when we see Earth from space, it's around 71 percent water, which accounts for its appearance.
The presence of water on Earth is one of the features that have given our planet the ability to sustain life. Another is its atmosphere. The atmosphere of Earth is around 300 miles (480 kilometres) thick, shielding Earth from space, but because air pressure decreases moving away from the planet, most of it is within 10 miles of the surface. The main composition of Earth's atmosphere is 78 percent nitrogen, 21 percent oxygen, 0.93 percent argon and 0.038 percent carbon dioxide. Without this atmosphere and its balance of gases, there would be no humans to see Earth from space.
The atmosphere contains the air that we need to breathe, and also protects us from the sun's rays, warms the planet in the daytime and cools it at night. When astronauts see Earth from space, the atmosphere can cause distortion, and similarly it limits our view when looking outwards through a telescope.
Apart from pressure decreasing as altitude increases, the Earth's atmosphere is not consistent throughout, but is composed of five different layers separating Earth from space.
The troposphere is the first layer, closest to the Earth's surface. This layer makes up half of the planet's atmosphere at a height of around five to nine miles (8-14.5 kilometres) and is where most of our weather occurs.
The stratosphere is next, and here the atmosphere becomes less dense. The stratosphere is where the ozone layer is, which protects us by absorbing harmful rays from the sun.
The mesosphere is the layer in which meteors burn up upon entry.
The thermosphere is the layer where auroras are formed, colourful light shows that are caused by electrically charged particles from the sun colliding with gases. This is also the layer in which the space shuttle orbits.
The exosphere is the uppermost layer of Earth's atmosphere, with a limit of approximately 6,200 miles (10,000 kilometres). It is a very thin layer, and the last thing that divides Earth from space.
The atmospheres of most planets reflect back light so that we can only see their upper layers, accounting for the colours they appear. Like Mars, however, our planet's atmosphere is transparent enough that we can see the surface of Earth from space, so its distinctive colours can show through, giving us the blue sphere that has captured our fascination ever since we were first able to see Earth from space for ourselves.
Anyone who was born after the first images were taken of Earth from space may find it difficult to imagine what it was like to not have a definite idea of how our planet would look. Even those born before have most likely become so used to seeing bright, clear pictures taken of Earth from space that they take them for granted now. Of course, it wasn't possible to obtain images of Earth from space until we were able to launch satellites or travel a sufficient distance upward to get a good view of Earth from space. Until then, scientists and artists alike tried to envision how Earth from space would look. Globes may have helped with this somewhat, and the first known was made in Greece over 2,100 years ago. The oldest surviving globe was made in Germany in 1492, and is interesting because it's missing the then-unknown continents of North America, South America, Australia and Antarctica, causing a flawed version of Earth from space. Martin Behaim, the globe's creator, was an acquaintance of Christopher Columbus, who set sail for the East Indies in the same year the globe was finished. The two shared the view that it was possible to sail around the world, although it was not such an unpopular view as is sometimes made out; most Europeans of the time also knew that the Earth was a sphere, and even ancient sailors had held this belief despite nobody having ever seen Earth from space. Behaim's globe, an impressive attempt to show how we would see Earth from space, is so highly valued today that it is kept in a secret location to stop theft or damage.
When artists tried to depict how they imagined the view of Earth from space would look, they were of course helped by the existence of an abundance of detailed maps. It was not much of a leap from there to take a guess at colours. The problem came with the cloud cover, as nobody could figure out quite how that would look, and so this was where most of the artists' attempts to draw Earth from space differed.
Camille Flammarion was a French astronomer and author, who wrote popular science books and early science fiction. He was also quite possibly the first person to attempt to depict how we would see Earth from space, back in 1894. For such an early attempt, it was surprisingly accurate. Howard Russell Butler was next to try, in the 1920s. Butler's painting showed most of the planet's surface as visible, with cloud mostly in bands around the Earth, with wide spaces between. This was in accordance with what was at the time a popular and up-to-date theory of how clouds formed and therefore what we expected the appearance of Earth from space to be.
Later, in the 1930s, Lucein Rudaux attempted painting a depiction of Earth from space, and did so by consulting world weather records. This was quite a feat back then, as such records were not as easily available as they are now. The result was a high level of accuracy, that showed some of the complexity we now know to exist in the view of Earth from space, with a mixture of different cloud forms. Rudaux also created a depiction from the point of view of looking down at Antarctica on Earth from space. In the 1950s, Chesley Bonestell produced a number of pictures of the Earth from space. However, he typically got the clouds wrong, painting them in very thin, sparse bands around the planet's surface. This was despite his reputation for excellent research skills, and the fact that he owned a copy of Rudaux's book in which it was explained how clouds were likely to look around Earth from space. Some people believe Bonestell may have painted the clouds as he did deliberately, so that the surface was more visible and thus more recognisable as a depiction of Earth from space.
In 1956, William Palmstrom created his own vision of Earth from space. Palmstrom also used world weather records, and was assisted by two scientists from the US Weather Bureau. The resulting painting is remarkably close to what the world would soon see in photographs of Earth from space for the very first time.
On 24 October 1946, the world was still recovering from the Second World War, and humanity had its eyes on the future. A V-2 rocket, originally developed as a weapon of war, found an exciting and positive new use when it was launched from the New Mexico desert, equipped with a camera to take photos of Earth from space.
A group of American scientists and military engineers launched the rocket from the White Sands Missile Range. One of these engineers had developed a 35mm film camera that could take a photo once every second, and had an early understanding of the importance that photos taken of Earth from space would play in understanding our planet. The rocket climbed to a height of 65 miles before falling back to the ground, breaking the camera in the process. Luckily, the film survived the impact thanks to its metal cassette, and the researchers were able to retrieve it and the images it held of Earth from space.
Four years later, the photos taken by the V-2 rocket were published, and for the first time the public were given a glimpse of what they would see looking down on Earth from space. Subsequent missions with V-2 rockets took further images of the Earth from space, some from as high as 100 miles. But the best known images of Earth from space were yet to come.
In 1990, an image was taken by the Voyager 1 space probe which is memorable not for its clear view of Earth from space, but for another reason entirely. The Pale Blue Dot, as it's known, was taken at a distance of approximately 3.7 billion miles (6 billion kilometres) and, as the name suggests, you can barely see Earth from space so far away. However, seeing Earth from space at such a great distance is a humbling experience that demonstrates the vastness of the universe and our small place within it.
Apollo 17 was the last in NASA's series of Apollo missions, and the most recent time humans landed on the moon. But one of the crew's most memorable achievements didn't involve the moon at all.
During the spacecraft's journey to the moon in December 1972, the crew captured a photo of Earth from space. The resultant image was given the official NASA designation AS17-148-22727 – but you might know it by its snappier name, The Blue Marble. The astronauts themselves were the ones who first considered that viewing Earth from space, it resembled a marble, and it's easy to see why.
The beautifully bright, clear image was possible because the astronauts had the Sun behind them, fully illuminating Earth from space. It was taken from a height of roughly 28,000 miles (45,000 kilometres) and allowed everyone to see for the first time what the astronauts saw when they gazed down upon Earth from space.
The photo has understandably achieved a high level of fame since it was taken, and is one of the most widely viewed photos in existence, and probably the most well-known image of Earth from space.
The Blue Marble was such an apt name for the appearance of Earth from space that NASA have re-used it for a series of images composed after the original.
In 2002, NASA publicly released a large set of satellite images of Earth from space, ranging from full composite images of the Earth from space lit by the sun, to pictures with cloud cover and images of night on Earth from space.
In 2005, a further set was released, dubbed Blue Marble Next Generation, and in 2012 new composite images of both the western and eastern hemispheres, taken by the Suomi NPP satellite looking down on Earth from space. Finally, in 2015, the Deep Space Climate Observatory satellite was launched, complete with the Earth Polychromatic Imaging Camera (EPIC), which takes continuous images of the sunlit side of the Earth from space.
The first public image from this satellite was released a few months after it launched, and the team behind it now regularly releases new images of Earth from space on their website.
Back in 2012, an image known as The Black Marble was released. It was composed of images taken of North and South America at night mapped onto existing Blue Marble images for a clear view of lights that can be seen on Earth from space. These lights range from gas flares and wildfires to city lights, but much of the natural lights were removed to place an emphasis on the city lights. The bright lights we project at night are one way humans have changed the view of Earth from space over the course of our existence, but not the only one.
From the International Space Station's orbit of roughly 250 miles (400 kilometres) above us looking at Earth from space, astronauts have confirmed that the Great Wall of China cannot be seen with the naked eye, dismissing the long-held belief that it can be seen on Earth from space. However there are a number of interesting man-made features that can be seen on Earth from space, showing how humans have changed the view in our relatively short time on the planet.
The lights of civilisation at night, seen on Earth from space, are a breathtaking sight. The contrast between cities of different sizes and populations causes a lot of variation in the amount of light, and it should probably come as no surprise that Las Vegas is a particularly brightly-lit city, that stands out even more in the darkness of the Mojave Desert as a beacon of life seen on Earth from space.
In 2001, construction began on an extravagant artificial island off the coast of Dubai. Palm Jumeirah is named because it is in the shape of a palm tree, and the island was created by dredging sand from the bottom of the Persian Gulf.
Later, the island was joined by another palm, Palm Jebel Ali, and a collection of islands in the shapes of countries of the world. All of these islands can be seen on Earth from space, from the ISS, and also from satellites, giving a unique and distinctive addition to the way the UAE coastline looks back on Earth from space.
Although it may not be possible to make out the Great Wall on Earth from space, astronauts aboard the ISS have managed to snap pictures of the pyramids in Egypt, showing that at least some ancient man-made structures can be seen on Earth from space.
However, it's important to remember that “on Earth from space” is a very broad term, and the orbit of the ISS differs greatly from some of our satellites, and what can be seen from low orbit may be completely invisible on Earth from space at a greater distance away.
It's interesting to know that some of the things that can be seen on Earth from space now weren't there when astronauts on Apollo 17 looked down on Earth from space. But how does it feel for people to see our home from such a great distance away?
Human beings are not really designed to comprehend something as vast as the universe and our small place within it, and hardly equipped to see for ourselves a distant Earth from space. Since astronauts first began to look down on Earth from space, they have described the incredible feelings of awe brought about by this life-changing experience.
Psychologists who have studied the phenomenon call it the “overview effect”, a term that was first coined by Frank Wright, who investigated it in his 1987 book. Wright is now involved in The Overview Institute, a group dedicated to studying the cognitive effects of space travel and how people are changed by seeing Earth from space.
One of the most striking things about viewing Earth from space is that man-made borders between states and countries are invisible, and a key feature of the overview effect is the feeling of unity among humans, and awareness of the insignificance of our divisions within the greater universe.
Seeing the relatively tiny Earth from space also brings about a sense of the importance of protecting our planet. Seeing the fragility of Earth from space, emphasised by how small it is within the universe, combined with its unique position as the only planet we know of that hosts life, impresses upon astronauts looking down at Earth from space that it is vital to care for our home.
Overall, those who have had a first-hand look at Earth from space often report an overwhelming sense of awe, a deep feeling of being connected to the rest of the universe, and inner peace and clarity as Earthly concerns drop away and fade into insignificance.
Neuroscientists believe that the overview effect caused by viewing Earth from space may be a similar phenomenon to spiritual experiences that occur here on Earth, and are keen to study the brains of space tourists seeing Earth from space. Until the average person can take a trip into space, however, we'll have to settle for looking at Earth from space from the comfort of our homes.
Many people have become so used to having access to satellite maps beamed down to Earth from space, that it can be surprising to think that Google Maps didn't exist before 2005. Since then, the availability of the internet giant's maps of Earth from space on computer and now even on our mobile phones have become such a useful part of life that it's easy to forget quite what an incredible achievement they are.
With Google's satellite maps also composited onto a globe in their Google Earth program, we're given a true astronaut's-eye view, letting us look at Earth from space – but with obstructions like clouds removed, and with the added power to rotate and search the planet as we wish. An idealised version of Earth from space.
Although you might imagine gathering satellite maps to be a reasonably straightforward process, it's actually far from it. Companies that sell satellite photos of Earth from space to other entities have their own high-resolution imaging satellites orbiting a few hundred kilometres above us taking pictures of Earth from space.
Because they are not as high as weather satellites, they are only able to capture a small part of the Earth from space each time they pass – around 1%, resulting in narrow strips of imagery. Often, most of what is captured each time is water. Add to this the effect of the sun's angle and obstruction by clouds and pollution, and you begin to see how long it can take to get enough satisfactory footage of Earth from space to assemble into a full map.
And, although what you see of Earth from space when you look at Google Maps might not be particularly recent, new images are constantly evaluated to see if they're an improvement over the existing ones, and the maps are regularly updated with better footage of Earth from space.
Although a large proportion of the images used for Google Maps come from satellites photographing Earth from space, not all of them do. Photos are also obtained by aeroplane, and even kites and balloons. But keeping with satellites, imaging Earth from space is only one small part of what they're capable of.
A number of satellites that are currently orbiting our planet collect different types of data from a variety of instruments they have onboard, which is sent back to Earth from space to help us better understand our planet and its atmosphere.
Terra is the flagship satellite of the Earth Observing System, which now consists of 18 satellites that observe Earth from space. Terra was launched in 1999, and its observations help us to gain a picture of the changing climate on Earth from space.
The satellite carries five instruments that collect different types of data on Earth from space, including surface temperature of the planet, cloud coverage, carbon monoxide levels and radiation.
All of this information when sent back to Earth from space allows scientists to closely monitor climate change and the connections between different functions. It can also monitor carbon absorption, so we can study how this differs around Earth from space.
Another satellite in the Earth Observing System is Aura. Aura features an instrument called the Microwave Limb Sounder, which allows researchers to view the atmosphere of the Earth from space, layer by layer from the ground up. This is vital for monitoring the gases that contribute to the hole on the ozone layer, and helps to evaluate the impact of clouds on climate change. The satellites of the Earth Observing System have allowed us to gain a deeper insight into our planet and how the atmosphere works, and are an invaluable tool in studying Earth from space.
Nowadays we are used to the idea of satellites orbiting our planet, monitoring its surface and sending data down to researchers. Sometimes, however, satellites looking down on Earth from space can be a lot more secretive.
Officially they're called reconnaissance satellites, more commonly they're known as spy satellites, and they're up there, orbiting and watching Earth from space. It's not known how many of them are currently in orbit, and although several nations have launched their own spy satellites, the majority of them belong to the USA and Russia.
When the Cold War was in full swing, America wanted to make sure they were fully aware of Soviet technological advances, and prepared for any planned attacks. Satellites were an obvious way, able to view Earth from space and to see places where people couldn't go. Of course, nowadays, we are used to the idea of satellites orbiting our planet, recording images, and beaming them back to Earth from space, where they can be received by a computer. However, this was not possible at the time, and another method of getting the pictures back to Earth from space had to be developed.
The Corona reconnaissance satellite project was kept secret until it was officially declassified by President Bill Clinton, in 1995. The Corona satellites used by the USA from 1959 to 1972 were fitted with cameras, which took a specially-designed 70mm film. The problem was getting the used film back to Earth from space. The solution to this problem is nothing short of incredible.
Once a film roll – which could be between 8,000 and 16,000 feet in length – was used up, it was ejected in a re-entry capsule, which was nicknamed a “film bucket”. The capsule had a shield to resist the intense heat caused by re-entry to the atmosphere of Earth from space, and this would be jettisoned at around 60,000 feet; meanwhile, a parachute deployed to slow the descent of the capsule. As if all of that wasn't amazing enough, a highly skilled US Air Force pilot would then have to catch the film bucket using an airborne claw attached to an aeroplane.
Such a delicate and precise operation is difficult to get right, and Corona originally suffered 13 failed attempts to send its film to Earth from space. However, in 1960, a roll of film was successfully recovered after being sent back to Earth from space, and the method was used many times afterwards as an inventive way to retrieve detailed pictures of Earth from space; the Corona “film bucket” system continued through improvements and refinements into some of its successors.
KH class, or “Keyhole” satellites are used nowadays to gather military intelligence on Earth from space for the United States, and were first launched more than 30 years ago.
The most recent versions of this series of satellites are often given the designation KH-12, and cost an estimated $1 billion each to produce. Their successors are set to being launching in 2018, with a replacement of the current fleet planned. Because of the nature of these satellites' purpose, however, it's not surprising that much about them is kept classified, and available information about them is sketchy at best. However, here are some things we do know about keyhole satellites.
The resolution of the black and white cameras onboard is 5-6 inches, meaning they can spot objects on that are 5 inches or bigger on Earth from space. Compare this with the resolution of a Corona satellite's camera, which was 6 feet! They orbit at an altitude of about 200 miles (322 kilometres), but we don't know how many of them are currently up in orbit viewing Earth from space.
With regards to the appearance of the KH-12 satellites, this too is classified information. However, there is speculation based partly on officially available information that they bear a resemblance to another object orbiting our planet and sending data to Earth from space, and one that we do know about – The Hubble Space Telescope.
The Hubble Space Telescope has been in orbit since 1990 and, although not the first of its kind, is one of the largest and arguably the most famous. The HST orbits from outside of Earth's atmosphere, allowing it to capture images at an extremely high resolution, away from the distorting effect of the atmosphere that separates Earth from space. Hubble enables scientists to view distant objects, beaming its data down to Earth from space as it captures images and other information from its various instruments.
The idea for a space telescope had first been proposed as far back as 1923, with the idea that clearer images could be captured outside our atmosphere, then sent back to Earth from space. It wasn't until 1962 that one of the HST's predecessors, the Orbiting Solar Observatory (OSO) was launched by NASA, and an orbiting solar telescope was also launched by the United Kingdom as part of their Ariel space program, both of which send images to Earth from space. These early attempts showed the potential for success, and on 24 April 1990, the Hubble Space Telescope was launched to begin sending images to Earth from space.
The HST is named after Edwin Hubble, who in the 1920s used the biggest telescope of his time, at the Mount Wilson Observatory in California. From the observatory, Hubble made a number of important discoveries, such as distant galaxies beyond the Milky Way, and evidence supporting the theory that the universe is expanding. Although he carried out important and influential work and made a significant contribution to science, Hubble was never awarded a Nobel Prize. This was because, during his lifetime, astronomy was not considered a part of physics, so he was ineligible for the prize.
Although this has now changed, the prize can't be given posthumously. The naming of the Hubble Space Telescope, however, has helped ensure that he is remembered, and that his work is widely recognised. Hubble himself would no doubt be excited at the images the HST has sent to Earth from space.
Like its namesake, the Hubble Space Telescope has made a huge contribution to our knowledge of the universe, and has an impressive list of achievements. It's one of the most useful scientific instruments in history, and scientists using data sent to Earth from space by the telescope have published over 12,800 papers. It has made over 1 million observations in its time, and the Hubble archive totals over 100 terabytes of data; it receives about 10 terabytes of new data sent to Earth from space every year.
One notable achievement of the HST began with scientists deciding to take a risk. Understanding that the telescope has the resolution needed to see distant galaxies, they turned it on what looked like a mostly empty part of space. It was then set to take a long exposure – 10 days long – while the scientists waited patiently for the HST to send its images to Earth from space. Normally, observations made with the telescope took just a few hours, so using up such a long amount of time that could have been used for something more definite was risky. However, when the data from Hubble was sent to Earth from space, it revealed an amazing 3,000 galaxies, of all shapes and sizes. This image was called the Hubble Deep Field.
Encouraged by the success of this first long exposure image, Hubble was used alongside other observatories to capture further images in high resolution and send them to Earth from space, with long exposures and using multiple wavelengths. This resulted in images such as the Hubble Ultra Deep Field and the Great Observatories Origins Deep Survey (GOODS), which gave us a look at even further parts of the universe. One of the most significant outcomes from these discoveries was that, by studying a type of pulsing stars within the galaxies observed by Hubble, scientists were able to calculate the age of the universe far more accurately than ever before. Where previously it had only been known that the universe was between 10 and 20 billion years old, thanks to the HST we not know that it has existed for 13.7 billion years, give or take a few hundred million years.
The Hubble Space Telescope continues to regularly make useful observations, and will continue sending data back to Earth from space until the end of its life span, which is expected to be at some point between 2030 and 2040. At this point there are plans to retrieve it and bring it back to Earth from space, so it can be displayed publicly.
With all the new galaxies we've discovered with the help of instruments like Hubble, people often wonder what's out there, and whether there's intelligent life elsewhere in the universe that visits Earth from space.
Although there are regular sightings of UFOs and reports of encounters with aliens, there is of course yet to be any substantiated evidence of any extraterrestrials visiting Earth from space. That does not mean, however, that there is no life out there, and it hasn't stopped scientists from searching for it.
In the fairy tale of Goldilocks and the Three Bears, the little girl was very particular about how she liked her chairs, porridge and beds. Astronomers use the term “Goldilocks zone” to refer to the area around a star in which conditions are “just right” for life to exist – not too hot or too cold, with the possibility of liquid water existing. There are already a few planets known to exist within this distance from their stars, and more will surely be discovered by instruments like Hubble sending data to Earth from space.
One method of searching for alien life is by the use of radio telescope. A radio telescope is an instrument that can detect radio signals reaching Earth from space, which usually comes from natural objects in space.
The SETI (Search for Extraterrestrial Intelligence) Institute uses radio telescopes in the hunt for signals that could originate from an advanced civilisation. When radio signals reach Earth from space, the scientists at SETI, which began operating in 1984, analyse the data for any signs of unnatural patterns that may have come from intelligent life elsewhere and made their way to Earth from space.
On 15 August 1977, a researcher named Jerry R. Ehman who was working on a SETI-related project with the Big Ear radio telescope at Ohio State University spotted something exciting. When looking through data gathered by the telescope, Ehman noticed a signal had reached Earth from space that looked precisely like what we might expect from radio transmissions beyond the Solar System. Ehman circled the numbers representing the signal and wrote “Wow!” next to it, leading to it becoming known as the Wow! Signal. Despite best efforts, researchers were never able to find a similar signal reaching Earth from space, leading Ehman himself to doubt it came from intelligent extraterrestrials.
Some scientists now believe the signal may have been caused by comets passing Earth, or perhaps was reflected from our atmosphere instead of reaching Earth from space, but we don't know for certain. Could the radio signal have been sent out by an intelligent species all the way to Earth from space?
The search for life elsewhere in the universe goes on, and statistically speaking with the numbers of galaxies we know about, life must exist somewhere. The big question is whether we will discover intelligent life, or more simple life forms. Time will tell. For now we are alone in the universe, but with so many instruments circling our planet and constantly sending useful information to Earth from space, we learn more every day about our home planet and its place within the universe.