SOHO: Exploring the Sun

Shifting magnetic fields on the surface of the Sun form loops which push out from the surface into the upper atmosphere or corona.

As the invisible magnetic loops arc out from the surface, the Sun’s plasma clings to the field adding the spectacular visual aspect to the loop as shown in the picture.

The loops known as “prominences” generally form in a single day and can last for months before collapsing back down to the Suns’ surface. Prominences generally do not release material into space although some leakage of particles does occur.

An important tool for studying the Sun is SOHO, the acronym for theSolar and Heliospheric Observatory. SOHO took the picture shown above in July of 1999.Artist_s_impression_of_the_SOHO_spacecraft_medium

SOHO is a joint ESA and NASA project which launched in December 1995. In general SOHO’s twelve instruments were built and assembled by ESA members. NASA was responsible for launching the mission and for day to day operations.

Quoting ESA description of SOHO’s mission objectives:

“SOHO was designed to answer the following three fundamental scientific questions about the Sun:

  • What is the structure and dynamics of the solar interior?
  • Why does the solar corona exist and how is it heated to the extremely high temperature of about 1 000 000°C?
  • Where is the solar wind produced and how is it accelerated?”

Clues on the solar interior come from studying seismic waves that are produced on the surface.

SOHO orbits the Sun in sync with the Earth at a distance of approximately 1.5 million miles from the Earth. Days to day operations are managed out of NASA’s Goddard space Center outside of Washington DC.

SOHO carries twelve instruments which:

  • Detect emissions from the Sun’s corona using them to estimate the corona’s temperature
  • Analyses passing solar particles measuring density and alerting Earth of impending storms
  • Provides full disc images of the Sun in four ultraviolet colors
  • Using two instruments classify particles by origin (Sun, Milky Way, or rom outside the galaxy)
  • Measure the velocity of surface oscillations which provide clues about the Sun’s internal structure
  • Create a permanent artificial eclipse using an occulter allowing the Sun’s atmosphere to be studied
  • Looks for comets
  • Measure changes in the height of the surface, contributing to an understanding of the Sun’s internal structure and processes
  • Use spectroscopy to measure the flow, temperature, density and dynamics of the interaction of the Sun’s uppermost atmosphere, the corona, with the level below it the chromosphere
  • Study the effect of solar wind on hydrogen atoms in the solar system
  • Measure the change in the Sun’s irradiance over time.

SOHO has been incredibly successful providing detailed measurements of the Sun’s surface and activity and providing Earth for the first time advance warning of potentially dangerous solar activity.

At a time in history where science has explained so much about our world, where very little is mysterious or considered beyond understanding, it is humbling to realize that we are only just getting to understand something as significant as our Sun.