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When the Blue Marble Becomes Black
Discover our world at night through the eyes of space science.NASA, Earth at night: our planet at brilliant darkness, 2019.
Source: https://www.nasa.gov/connect/ebooks/earthatnight_detail.html
Speaking of the photograph of Earth in space, the image most of us would recall is probably the classic photo taken by the Apollo 17 crew on December 7, 1972, dubbed the “Blue Marble”as shown below. The color of an object is actually the color of the light reflected while all other colors are absorbed. Since approximately 70% of Earth’s surface is covered by deep ocean water, Earth appears as a blue marble when viewed from space during daytime hours. Clouds suspended in Earth’s atmosphere provide the white swirls.
Enshrouded in nighttime darkness, however, Earth appears more as a black marble from space—one shimmering with light. The human search for light in darkness is long- standing. Many of our myths and religions focus on this search, yet it is only within the past century that humans have gained the ability to take flight—first to the skies and later into space—providing new vantage points from which to view Earth and the twinkling lights below, clearly visible at night.
In December 2019, NASA released an e-book, Earth at night: our planet at brilliant darkness, bringing together the lastest dazzling photographs and images from space of our planet’s nightlights. It can be downloaded for free on its website.This books show us new ways to discern the nuances of light created by natural and human-made sources, such as auroras, wildfires, cities, phytoplankton, and volcanoes. Most interesting and unique to Earth, is the nighttime visible illumination emitted from our planet that is associated with human activities. Whether purposefully designed to banish darkness (such as lighting for safety, industrial activities, commerce, and transportation) or a secondary result of (such as gas flares associated with mining and hydrocarbon extraction activities, or nocturnal commercial fishing), anthropogenic sources of nighttime light are often broadly distributed in space and sustained in time—over years and even decades.Because these light sources are inextricably tied to human activities and societies, extensive and long-term measurement and monitoring of Earth’s anthropogenic nocturnal lights can provide valuable insights into the spatial distribution of our species and the ways in which society is changing—and is changed by—the environment on a wide range of time scales.Over the past four decades, sensitive imaging instruments have been operated on low-Earth-orbiting satellites to measure natural and human-caused visible nocturnal illumination, both reflected and Earth-generated. The satellite sensors provide unique imagery: global coverage yet with high spatial resolution, and frequent measurements over long periods of time. The combined, multisatellite global nocturnal illumination dataset contains a treasure trove of unique information about our planet and our species—and the interactions between society and natural processes.Satellite images of Earth at night have served as a fundamental research tool, while also stoking public curiosity. These images paint an expansive and revealing picture, showing how humans have illuminated and shaped the planet in profound ways since the invention of the light bulb 140 years ago.Where do nightlights come from?The night side of Earth twinkles with light, easily observed by orbiting satellites. The most obvious source comes from city lights, but as one looks closer, much more becomes discernible. Even at some distance from human settlements, light still shines: Wildfires and volcanoes rage; gas flares glow like candles; auroras dance across the polar skies; moonlight and starlight reflect off surface water, snow, and deserts; and clouds are easily seen. Even the air and ocean sometimes glow.
The top image shows the nightlights of Australia as observed by the VIIRS DNB on the Suomi NPP satellite in April and October 2012. The composite image includes manmade light sources and the light from wildfires. The lower map is a mosaic showing the burned areas of the landscape (red) from October 11–24, 2012, combined with urban areas (black). In effect, the lower map shows where fires burned that month. side from the fires, some of the nightlights appearing in uninhabited areas can be attributed to lightning, flares of natural gas and other activities from oil drilling or mining operations, and fishing boats—all of which can show up as points of light.Viewing Earth at night from space reveals a distinctly human story. As one gazes upon the points of light in images captured from orbiting sensors, discerning eyes begin to see the fingerprints of human presence: from the glow of megacities and the pinpoints of bright light produced by fleets of fishing boats at sea, to gas flares glowing like candles in the darkness, lights show where we have made our homes, established industries, mined natural resources, and built roads.It quickly becomes evident looking at nightlight data that human activity is highly influenced by Earth’s natural features and processes, or physical geography. For example, the vital link between humans and water is quite clear. Nearly half the world’s population lives along or near coastlines. Others live along rivers and freshwater bodies. Most population centers tend to be along coastlines, near rivers, or near major over- land transportation hubs (e.g., highways, railroads) that cut slivers of light through the darkness between cities.In general, our species tends to avoid settling in regions with harsh climates, in mountainous areas with steep terrain, and where basic resources like food and water are limited (e.g., deserts). Accordingly, more light is clustered around regions where the climate is moderate, terrain is flat, resources are plentiful, and soil is fertile.Areas with the brightest light are generally the most urbanized—but not necessarily the most populated. Lights show how far urban sprawl extends, as well as areas where growth is occurring or where growth has not yet occurred. Cities usually have many people concentrated in a small area, so electricity usage is high. Poor areas may have large populations but low availability or use of electric lights. These signals from anthropogenic nightlights provide clear indicators of how we’ve settled our planet and—with some analysis—what we do with our energy.
The city of Bangkok, the capital and largest city in Thailand, illuminated by city lights, 2017
Grid of City Blocks—Phoenix, Arizona
This astronaut photograph, taken on March 16, 2013, includes parts of several cities in the metropolitan area, including Phoenix (image right), Glendale (center), and Peoria (left).Like many large urban areas of the central and western United States, the Phoenix metropolitan area is laid out along a regular grid of city blocks and streets.
Dazzling Coastlines—Italy
City lights clearly delineate the boot of Italy in this panorama taken by astronauts onboard the ISS on October 21, 2014. Looking east on this clear night, the pattern of nightlights shows populations concentrated mainly along the coastlines, but also in the Po River Valley of northern Italy.
Living on Fertile Land—Nile River, Egypt
The Nile River and its heavily populated delta look like a brilliant, long- stemmed flower in this photograph of the southeastern Mediterranean Sea, as seen from the ISS on October 28, 2010. The Cairo metropolitan area forms a particularly bright base for the flower. urbanized regions and infrastructure along the Nile River become apparent.
The Winding Seine River and the City of Light—Paris, France
Around local midnight on April 8, 2015, astronauts onboard the ISS took this photograph of Paris, often referred to as the “City of Light.” When viewed from low Earth orbit, the pattern of the street grid dominates the Parisian night, providing a completely different set of visual features from those visible during the day. The brightest boulevard in the dense network of streets is the Avenue des Champs- Élysées, the historical axis of the city, as designed in the seventeenth century. This grand avenue joins the site of the former royal Palais des Tuileries to the star-like meeting place of eleven major boulevards at the Arc de Triomphe.
Lighting Paths to Oil—Qatar
In the photograph below, taken from the ISS on October 13, 2012, the nightlights of Qatar show informative demographic detail that is very difficult to discern in daylight images—especially in deserts, where even large cities can be hard to see. The brightest group of lights at image center is the capital city, Doha, with the neighboring smaller ports of Ad-Dahirah and Umm Sa’id to the north and south.
Snaking Along Canyon Cliffs—Haifa, Israel
Differences in Socio-Economic Strategies—Korean Peninsula
In this north-looking view, it is immediately obvious that Seoul is a major city and that the port of Gunsan is minor by comparison. There are 25.6-million people in the Seoul metropolitan area—more than half of South Korea’s citizens—while Gunsan’s population is 280,000. North Korea is almost completely dark compared to neighboring South Korea and China. Its capital city, Pyongyang, appears like a small island, despite a population of 3.26 million (as of 2008). The light emission from Pyongyang is equivalent to the smaller towns in South Korea. Coastlines are often very apparent in night imagery, as shown by South Korea’s eastern shoreline, but the coast of North Korea is difficult to detect. These differences are illustrated in the significant differences in per capita power consumption between the two countries, with South Korea at 10,162 kilowatt hours and North Korea at 739.
The nighttime image shows Argentina’s nightlights as observed by the VIIRS DNB on the Suomi NPP satellite in 2016. Most people reside in the country’s main cities, including Córdoba and Santa Fe. A mere 10 percent of Argentina’s population lives in rural areas.
Many of the largest cities and towns in Pakistan are clustered along the Indus. Karachi lies along the southernmost stretch of the river, near where it empties into the Arabian Sea at the Indus River Delta. The border between Pakistan and India stands out among the nightlights of this region. For security purposes, India has installed thousands of kilometers of floodlights along the border.
These nighttime photographs taken by astronauts onboard the ISS reveal the unprecedented growth of Shanghai, China, between March 10, 2003 and February 28, 2018.The rapid pace of development has changed Shanghai’s natural ecosystems. Wetlands in the region have declined due to sea level rise, erosion, dredging, and the construction of water-storage infrastructure. The creation of new coastal land—by piling sediment onto tidal flats in a process called land reclamation—has also played a key role.
The two images below show differences in nighttime lighting between 2012 and 2016 in Syria and Iraq, among several Middle Eastern countries. Each image is drawn from a global composite that was made by selecting the best cloud- free nights in each month over each land mass. Six years of war in Syria have had a devastating effect on millions of its people. One of the most catastrophic impacts has been on the country’s electricity network. The changes are most dramatic around Aleppo, but also extend through western Syria to Damascus. Over the four years shown, lighting increased in areas north of the Syrian border in Turkey and to the west in Lebanon. In Iraq, some northern sections near Mosul saw a decrease in light over the years, while areas around Baghdad, Irbil, and Kirkuk saw increases.CityReads ∣Notes On Cities"CityReads", a subscription account on WeChat,
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