Lesson: Solar Wind Velocity (Grades 9-12)

Teacher information

The changing position of a comet's tail as it circumnavigated the sun lead observers to predict a solar wind , something blowing out from the sun causing long streamers behind the comet just as a strong wind causes long hair to blow away from a face. This wind was confirmed in 1959 by the Soviet Luna 3 spacecraft and has been the object of study ever since.

The solar wind consists of charged particles, mainly protons and electrons, emanating from the Sun in all directions at speeds of several hundred kilometers per second and carries a magnetic field. The solar wind also contains, in much smaller amounts, positive ions stripped of many of their electrons by the extremely high temperatures of the Sun.

The very active, very hot corona continually expands outward moving at velocities of hundreds of kilometers per second, a million miles per hour! This allows these protons and electrons to escape the gravity of the sun and pour out into space well beyond the solar system. The Earth's magnetic field (magnetosphere) protects us from these particles, acting like a rock in a stream, diverting the solar wind around us.

The solar wind reaches earth if a break is created in the magnetosphere due to the magnetic field orientation of the solar wind being directly opposite to that of the Earth. At that time there is a momentary opening of the magnetosphere that protects us and some solar wind leaks in.

The solar wind is less energetic than galactic wind (cosmic radiation) by orders of magnitude and can be identified by these energetic differences. Solar wind energies are 1-2 keV (thousand electron volts) per nucleon. A large eruption from the sun (Coronal Mass Ejection, CME) could produce solar particles with energies of 10 MeV (million electron volts). Cosmic radiation energies are in excess of several billion electron volts.

Activity: Mapping Solar Winds to Solar Images

Materials:

• MTOF/PM GRAPH: Carrington Rotation 1913
• Printouts of EIT images for Aug 27, 1996, and Coronal Plots.
• Individual student science notebooks or paper.

Type of Activity:

• Lecture/Discussion
• Calculations of when solar wind left the sun

Procedure:

1. Study MTOF/PM GRAPH: Carrington Rotation 1913
   • Using V_sw plot, what was the average velocity of the solar wind on August 30?
     • ANSWER: 600 km/s
2. Using this velocity data and location of SOHO, students calculate when this wind left the sun and when it will hit the Earth (assuming it could get through the magnetosphere).
   • ANSWER:
     

     1. 150,000,000 km(distance from Earth to sun)
        -1,500,000 km (distance from Earth to SOHO)

        148,500,000 km (distance from Sun to SOHO)

     2. Using Distance = Rate x Time,

        148,500,000km/600 km/sec = 247500 sec (time for solar wind to reach SoHO)

     3. Convert seconds to hours and days:

        247500 sec/3600 sec/hour = 68.75 hours

        68.75 hours/24 hours/day = 2.9 days

     4. Therefore, the solar wind being recorded on August 30 left the sun 2.9 days before, namely on August 26/27.

     5. When will this wind reach the Earth?

        1,500,000 km/600 km/sec = 42 min, from the time it hit SOHO.

3. A Solar wind of 600 km/sec is a fast solar wind. It has been proposed that fast solar winds are emitted from coronal holes. Did, in fact, a coronal hole exist during August 27 in an area that was in our direct line of sight? Remember, the solar wind that affects SOHO and therefore the Earth is at the center of the Sun in a direct line with us.
   • ANSWER: Using EIT images for Aug 27, 1996 along with Coronal plots from NOAO for those dates, it can be shown that a large coronal hole existed at the equator.
4. Students create a graph of solar wind velocities (y-axis) versus days for the wind to reach the earth (x-axis).
   • Given velocities of 200 km/sec to 800 km/sec (in units of 50 km/sec), have students calculate the times and plot the results.
   • Have students predict times for 900 and 100 km/sec.
5. Independent Student Research
   • Students follow mappings through 3-5 rotations during the school year. Did the velocities change over time? Were the higher velocities initiated at coronal holes?
   • Research reference: Solar Wind Campaign Proposal:
   • Solar Wind Bibliography
   • Is there enough time to warn communications satellites to shut down before a big event coronal mass ejection (CME) takes place? How fast are CME's traveling? How accurate would these predictions be? Research into past disruptions on earth.

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Connections to National Standards:

• National Science Education Content Standard A, B, D, E, H:
  • All students should develop abilities necessary to do scientific inquiry.
  • All students should develop an understanding of motions and forces.
  • All students should develop an understanding of origin and evolution of the earth system.
  • All students should develop understanding about science and technology.
  • All students should develop understanding of science as a human endeavor and historical perspectives
• Benchmarks for Science Literacy:
  • Students should know that telescopes collect information from across the entire spectrum of electromagnetic waves, space probes send back data from the remote parts of the solar system and that increasingly sophisticated technology is used to learn about the universe.
• Standards for School Mathematics:
  • Students should estimate, make and use measurements to describe and compare phenomena; select appropriate units and tools to measure to the degree of accuracy required in a particular situation; develop formulas and procedures for determining measures to solve problems.