When the Sun goes down, the lights come on. Seen from space, the nightlights of our world are mesmerizing. But more than just pretty pictures, there's a lot to be learned from all those glittering lights.
This image of continental USA at night is a composite assembled using data taken from the Suomi NPP satellite in April and October 2012.
Scientists at NASA's Goddard Space Flight Center use algorithms to filter extraneous light from images, like this one of Italy in 2016, collected by the NASA-NOAA Suomi-NPP satellite.
The Indus River in Pakistan emerges in nighttime satellite imagery. The brighter, more reflective land beyond the dark band of farmed land is desert.
The border between Pakistan and India is delineated on the right by thousands of kilometers of floodlights.
Many of the largest cities and towns in Pakistan are clustered along the Indus River.
Karachi lies along the southernmost stretch of the river, near where it empties into the Arabian Sea at the Indus River Delta.
After Hurricane Maria tore across Puerto Rico in September 2017, it rapidly became clear that the destruction would pose daunting challenges for first responders. Quickly knowing where the power is out - and how long it has been out - allows better deployment of rescue and repair crews.
Teams of scientists at NASA worked long days to ensure that groups like the National Guard and the Federal Emergency Management Agency (FEMA) got high-quality satellite maps of power outages in Puerto Rico.
These before-and-after images of the night lights in San Juan are based on data captured by the Visible Infrared Imaging Radiometer Suite (VIIRS) “day-night band” on the NASA-NOAA Suomi NPP satellite.
To make the VIIRS data more useful to first responders, the NASA Goddard team scaled the observations onto a base map that emphasized the locations of streets and neighborhoods.
This map shows where the intensity of light decreased (orange), increased (purple), and stayed the same (white) between 2012 and 2016 in the U.S. Midwest.
The increase in light along Interstate 90 between Chicago and Rockford, Illinois is associated with a multi-year project to widen the road.
The cluster of bright light at the edge of Lake Michigan is Chicago. I90 is the purple (new) line of light to the left of the city.
This image shows part of the Atlantic coast of South America.
Buenos Aires is the cluster of brightest lights on the lower left.
Rio de Janeiro is at the top right, and Sao Paulo in between.
Away from the cities, some lights in the image may be wildfires (inland) or fishing boats (offshore).
This map shows the change in lighting intensity and location in Texas and Louisiana from December 2012 and 2013 to the average light output for the rest of 2012 to 2014.
Green shading marks areas where light usage increased in December; yellow marks areas with little change, and red marks areas where less light was used.
Nighttime lights around many major U.S. cities shine 20 to 50 percent brighter during Christmas and New Year when compared to light output during the rest of the year.
Scientists using the NASA-NOAA Suomi-NPP satellite saw nighttime lights in some Middle East cities 50 to 100 percent brighter during the holy month of Ramadan.
This map shows changes in lighting intensity in Cairo (left) and the Arabian Peninsula during Ramadan in 2012–2014 to the average light output for the rest of 2012 to 2014.
Green shading marks areas where light usage increased during the holy days; yellow marks areas with little change; and red marks areas where less light was used.
Although some of the poorest and most devout areas around Cairo observed Ramadan without significant increases in light use, during the Eid al-Fitr celebration that marks the end of Ramadan, light use soared as the neighborhoods appeared to join in the festivities.
Nightlights can show us where people live and how that can be influenced by the landscape.
In this 2016 composite image of Iceland, the capital, Reykjavík, is the large, bright area that clearly stands out in the southwest. The city is home to almost half of the country's population.
The interior of Iceland is rugged, high in elevation, sparsely vegetated, and cold!
Sprinkled with volcanoes, ice caps and hot springs, it's a remarkable place to visit, but nightlights show us not many people want to live there.
When this nightlight composite was published in 2012, observers wondered how there could be so much light in sparsely populated areas of Australia's Western Outback.
The lights were a function of composite imaging. Fires and other lights that were detected on one day were integrated into the composite, multi-day picture despite being temporary. Because different lands burned at different times, the cumulative result is the appearance of a massive blaze.
On July 15, 2012, the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured this nighttime view of the aurora australis, or “southern lights,” over Antarctica’s Queen Maud Land and the Princess Ragnhild Coast.
The sensor detected the visible auroral light emissions as energetic particles rained down from Earth’s magnetosphere and into the gases of the upper atmosphere.
The slightly jagged appearance of the auroral lines is a function of the rapid dance of the energetic particles at the same time that the satellite is moving and the VIIRS sensor is scanning.
Light from the aurora was bright enough to illuminate the ice edge between the ice shelf and the Southern Ocean. At the time, Antarctica was locked in midwinter darkness and the Moon was a waning crescent that provided little light.
Explore more of Earth from space online
You can now browse natural and false-color images of Earth online within hours of them being captured by satellite, through NASA’s imaging and mapping services.
The Global Imagery Browse Services (GIBS) and Worldview tools are freely available online to the science community and public. This is thanks to the research team for NASA's Earth Observing Satellite Data and Information System (EOSDIS).
The team has also reprocessed 2012 data with the new techniques, so researchers can also compare and contrast light sources from past years.
View and download images and read stories of night-light science on the NASA Earth Observatory Earth at Night website.
VIIRS images from the NASA-NOAA Suomi-NPP satellite provided by Miguel Román, NASA Goddard Space Flight Center.
Images and text from NASA Earth Observatory by Jesse Allen, Mike Carlowicz, Kate Ramsayer, Robert Simmon, Joshua Stevens, Kevin Ward.
Curation by Debra Gersh Hernandez, NASA Headquarters.