A Look Back at NASA Solar Missions
Engineers examined the Solar and Heliospheric Observatory during assembly
ESA engineers examined the Solar and Heliospheric Observatory during assembly at the Matra Marconi Space facility.
Credits: SOHO (ESA & NASA)
Twenty years ago, the Solar and Heliospheric Observatory, a cooperative effort between NASA and the European Space Agency, launched into space and revolutionized our study of the sun and a scientific discipline called heliophysics – the study of how the sun’s influence spreads out in all directions, able to dramatically affect the space environment near Earth and throughout the solar system.
But the field was far from its infancy when that observatory, also called SOHO, launched on Dec. 2, 1995. In fact, it can trace its roots back to Thomas Harriot, who first saw sunspots through a telescope in 1610.
The study really took off about 130 years ago following Dutch astronomer Pieter Zeeman’s discovery that a magnetic field, or a field of force generated by electrical currents, alters some spectral lines. Within a decade, American astronomer George Ellery Hale used Zeeman’s discovery to demonstrate that sunspots contained strong magnetic fields. But it took NASA missions to get off the ground – literally.
“When you can get your instrument above the atmosphere, you begin to be able to see things you couldn’t see before,” said Keith Strong, heliophysicist emeritus at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Goddard heliophysicist Joe Gurman said gathering observations from above the atmosphere was one of the first science goals of NASA as an agency – and an absolute necessity for studying the sun because Earth’s atmosphere absorbs or deflects much of the light the sun emits: most ultraviolet radiation, X-rays and gamma-rays.
After World War II, when there was a growing recognition of solar activity’s influences on radio frequency propagation in Earth’s upper atmosphere, scientists began to study that activity more intensively. They used leftover German rockets to soar above Earth’s atmosphere to measure emission in wavelength ranges absorbed by atmospheric gases, and found that the sun's ultraviolet radiation varied wildly from year to year. But these rocket missions were limited. They could only launch to the edge of space for five to 10 minutes, and though they got marginally better over the years, it still wasn't enough. Scientists needed something capable of long-term observation, so NASA developed spacecraft called the Orbiting Solar Observatories to study solar activity.