These scientists watch the sun to better understand the Earth

Meet the fans of big data who are helping to shape the scientific consensus on climate change – and revealing new information about the workings of Earth’s favorite star.

For more than four decades, generations of scientists, both in Colorado and beyond, have kept a close eye on the sun. They use a range of tools, from ancient maps to satellites in space, to track the sun’s energy output as it cycles between moods—blazing bright, then dimming back down again over years and decades.

These researchers, and their datasets, may not often make the headlines, said Odele Coddington, a research associate at the Laboratory for Atmospheric and Space Physics (LASP) at CU Boulder. But in a series of studies, Coddington and her colleagues have expanded scientists’ understanding of how the brightness of this star shifts over time. In doing so, they’ve helped to show how humans, not the sun, are changing the planet’s climate at a dangerous pace.

“Data stewardship isn’t always glamorous,” Coddington said. “But these data are really important for teasing out how the sun’s brightness changes, now and in the past.”

She would know. For more than 10 years, Coddington has helped to make precise space-based measurements of the sun’s energy output and convert them into data that climate scientists around the world can use. She and her colleagues are also trying to jump further back in time, drawing on historical records to estimate the sun’s activity during the time of Galileo Galilei and even earlier.

It’s a pursuit that leaves little room for error, said Judith Lean, who retired in 2019 as a solar scientist at the US Naval Research Laboratory.

“The sun’s energy is so strong, there’s so much energy, you really need to get your numbers right,” she said.

A fickle star

Odele Coddington

Lean, who now collaborates with Coddington as a part-time research associate at LASP, has investigated the sun’s variability and its influence on Earth for more than 30 years. And, she noted, scientists have learned a lot about the orb during her career.

Star-gazers, of course, have long known the sun is hot-really, really hot. More than 1 million Earths could fit inside the sun. Its core reaches temperatures of millions of degrees, toasty enough for hydrogen atoms to meld together into helium atoms through nuclear fusion.

Then the space era arrived.

In 1978, NASA launched a satellite called Nimbus 7 to measure the magnitude of the sun’s total brightness at Earth, which scientists call “solar irradiance.” It was followed by a series of spacecraft carrying increasingly advanced instruments, including the Solar Radiation and Climate Experiment (SORCE). This intrepid vehicle was launched in 2003 and remained in operation until 2020. It also carried four instruments designed and built by teams at LASP.

From these orbiting sentinels, scientists realized the sun’s energy isn’t constant at all but goes through regular cycles lasting about 11 years. Between relatively quiet periods, the sun’s energy output increases until it reaches a “solar maximum.” At that stage, dark regions called sunspots crawl more often over the solar surface. Flares and events called coronal mass ejections frequently burst from the sun’s atmosphere.

Lean noted that these cycles matter. If you want to understand how humans are changing the Earth’s environment, including its climate and atmosphere, you first need to grasp how the sun influences the planet through natural processes.

“If we didn’t have the sun, we wouldn’t have a greenhouse effect,” Lean said. “It’s the balance between incoming energy from the sun and the outgoing energy radiating from Earth to space that establishes temperatures on the planet. We now know that this incoming solar energy changes with time.”

Historical records


Technicians work on a spacecraft in a cleanroom

Click to enlarge

The SORCE spacecraft in a clean room before its launch. (Credit: NASA)

Which is where Coddington comes in.

She and her colleagues, including Lean, have built some of the most detailed records of ups and downs in the sun’s brightness over the last 20 years using data from space instruments. They include sensors aboard SORCE and, more recently, a new LASP instrument that sits on the International Space Station called the Total and Spectral Solar Irradiance Sensor (TSIS-1). Coddington and her team at LASP provide quarterly updates of their solar irradiance records to the National Oceanic and Atmospheric Administration (NOAA). Scientists can then plug these numbers into global climate models—huge computer simulations that recreate the many factors that shape Earth’s climate and soaring temperatures over time.

Earlier this year, Codding and her colleagues received major recognitions from an international body called the Committee on Earth Observation Satellites. The committee named one of the team’s records of the sun’s irradiance during a week in December 2019 as the “new solar irradiance reference spectrum.” In other words, international scientists consider these solar data to be the most accurate determination of the sun’s irradiance during a solar minimum.

Coddington also isn’t content to remain in the modern era. She explained that, for centuries, scientists from Chinese astronomers in the courts of Song dynasty emperors to Galileo himself have kept track of sunspots-those shadowy features that dot the sun’s surface. These early researchers even drew maps of their observations, which are coming in handy today. In a counterintuitive twist, when you see more of these dark blotches on the sun, the star tends to grow brighter overall.

Coddington, Lean and their colleagues have drawn on those same maps to try to estimate just how much the sun’s variations in energy influenced Earth before the space era. Their most recent findings push that record back to 1610 AD

“People are uncovering sunspot records from even further back in the past,” Coddington said. “From Chinese artifacts or tucked away in some file cabinet somewhere, there’s historical data recovery still being done today.”

For the scientist, the findings show just how many researchers have come together over the years to establish the scientific consensus on climate change – from solar scientists and geologists to biologists, mathematicians, historians and many others.

It’s a community Coddington is proud to be a part of.

“I wouldn’t even know how to begin to list out all of the names,” she said, “the whole family tree of scientists around the world who have had their fingers in shaping everything from the theory of how the sun behaves to observing its activity at the surface.”


As a global leader in climate, environmental and energy research, the University of Colorado Boulder is partnering with United Nations Human Rights to co-host the Right Here, Right Now Global Climate Summit in fall 2022.

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