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July 22, 2004
NASA Goes to the “SORCE” of Earth Sun-blockers
Scientists using measurements from NASA’s Solar Radiation and Climate Experiment (SORCE) satellite have discovered that Venus and
sunspots have something in common: they both block some of the sun’s energy going to Earth.
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Using data from NASA’s SORCE satellite, scientists noticed that, when Venus came between the Earth and the sun on June 8, the other planet
reduced the amount of sunlight reaching Earth by 0.1 percent. This Venus transit occurs when, from an earthly perspective, Venus crosses in front of
the sun. When it happens, once every 122 years, there are two transits eight years apart. The next crossing happens in 2012 and will be visible to
people on the U.S. West Coast.
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“Because of its distance from Earth, Venus appeared to be about the size of a sunspot,” said Gary Rottman, SORCE Principal Investigator
and a scientist at the Laboratory for Atmospheric and Space Physics (LASP), at the University of Colorado at Boulder. The SORCE team had seen similar
reductions in the sun’s energy coming Earthward during the October 2003 sunspot activity.
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In October 2003 the Earth-bound sunlight dimmed 0.3 percent for about four days, due to three very large sunspot groups moving across the face of the
sun.
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“This is an unprecedented large decrease in the amount of sunlight, and it is comparable to the decrease that scientists estimate occurred in
the seventeenth century,” Rottman said. That decrease lasted almost 50 years, and was likely associated with the exceptionally cold
temperatures throughout Europe at that time, a period from the 1400s to the 1700s known as the “little ice age.”
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Solar conditions during the little ice age were quite different, as there were essentially no sunspots. Astronomers of the time, like Galileo, kept a
good record of sunspot activity before and during the period, encountering only about 50 sunspots in 30 years.
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Rottman said, “Something very different was happening during the seventeenth century, and it produced a much more permanent change in the
sun’s energy output at that time.” Today, the large sunspots are surrounded by bright areas called “faculae.” Faculae more
than compensate for the decrease in sunlight from sunspots, and provide a net increase in sunlight when averaged over a few weeks.
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The large number of sunspots occurring in October/November 2003 indicated a very active sun, and indeed many very large solar flares occurred at that
time. SORCE observed the massive record-setting solar flares in x-rays. The flares were accompanied by large sunspots, which produced a 0.3 percent
decrease in the sun’s energy output. SORCE simultaneously collected the energy from all wavelengths, something that had never been done
before.
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“The SORCE satellite instruments provide measurements of unprecedented accuracy, so the sun’s energy output is known with great
precision, and precise knowledge of variations in the sun’s energy input to Earth is a necessary prerequisite to understanding Earth’s
changing climate,” said Robert F. Cahalan, SORCE Project Scientist and Head of the Climate and Radiation Branch at NASA’s Goddard Space
Flight Center, Greenbelt, Md.
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The SORCE measurements provide today’s atmospheric and climate scientists with essential information on the sun’s energy input to the
Earth. These measurements also will be valuable to future scientists, who will be relating their view of the world back to conditions existing today.
Likewise Galileo’s findings about the sun almost 400 years ago have increased in value as understanding of the sun and its importance for Earth
has advanced.
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For more SORCE information and images on the Internet, visit:
http://www.gsfc.nasa.gov/topstory/2004/ 0730sunblockers.html
and
http://lasp.colorado.edu/sorce/
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Contacts:
Gretchen Cook-Anderson
Headquarters, Washington
Phone: 202/358-0836
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Rob Gutro
Goddard Space Flight Center, Greenbelt, Md.
Phone: 301/286-4044
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Jim Scott
LASP, University of Colorado, Boulder
Phone: 303/492-3114
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The Venus Sun-Block
Venus Transit seen by the SXI (Solar X-ray Imager) on NOAA’s GOES spacecraft. Credit: NASA/NOAA
Venus Blocks Some of Earth’s Sunlight
When Venus came between the Earth and the Sun for 6 hours on June 8th, it reduced sunlight to Earth by one-tenth of a percent. SORCE
measured a drop in the Sun’s energy by about 1.36 Watts for each square meter of Earth’s cross-section. CREDIT: NASA, LASP
Colorado
Sunspots Block Some of Earth’s Sunlight
In October 2003, large sunspots moving across the Sun blocked 3/10ths of one percent of sunlight to Earth for about 4 days.
CREDIT: NASA, LASP Colorado
What is the SORCE Satellite?
NASA’s SOlar Radiation & Climate Experiment, or SORCE spacecraft is helping answer questions like: How much of climate change is due
to man’s activity versus naturally occurring? What role does the Sun play in our climate and how do changes within the Sun affect us? How
much does the Sun vary on a daily and long-term basis? CREDIT: NASA
The Little Ice Age and Maunder Minimum Examined
How much can solar variability affect us? Unusually low solar activity (marked by fewer sunspots observed) between 1645-1715, called the
‘Maunder Minimum’ likely triggered the ‘Little Ice Age’ in regions like Europe and North America. Aert van
der Neer’s painting, “Sports on a Frozen River,” shows a period where global temperatures differed enough to freeze
rivers and cause other far-reaching consequences. Image “Winter Scene with Frozen Canal” (detail) by Aert van der Neer Courtesy:
Fine Arts Museums of San Francisco, Gift of Mr. & Mrs. Prentis Cobb Hale 1960.35
Why Sunspots?
In this case, the low solar activity depicted by fewer sunspots) during the Maunder Minimum meant decreased UV radiation which impacted the
protective ozone formation in the upper atmosphere (stratosphere). The changes, then, in the upper atmosphere, feed down to the surface climate and
affect many systems, including the Arctic Oscillation/North Atlantic Oscillation. These are jet stream systems that would transport warmer air to
America and Europe. SUPER: NASA / ESA
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