Lesson: Differential Rotation of the Sun (Grades 9-12)

Teacher Information

The Sun has a north and south pole, just as the Earth does, and rotates on its axis. However, unlike Earth which rotates at all latitudes every 24 hours, the Sun rotates every 25 days at the equator and takes progressively longer to rotate at higher latitudes, up to 35 days at the poles. This is known as differential rotation.

The Sun rotates in the same direction as Earth. The Carrington Rotations are named for Richard Carrington, an astronomer who first noted that sunspots rotate every 27.28 days. Rotations are numbered starting with 9 November 1853. The 1996 Jun 18 - 1996 July 15 rotation is rotation number 1924.

This lesson uses SOHO data from the EIT(Extreme-ultraviolet Imaging Telescope) instrument on the spacecraft.

Activity: Longitude and Latitude

Materials:

• Globe indicating longitude and latitude lines.
• Printouts of EIT images and a NOAO spherical grid.
• Individual student science notebooks or paper.

Type of Activity:

• Lecture/Discussion
• Location of places on Earth
• Plotting active regions on the sun.

Procedure:

1. Review longitude and latitude
   • Students locate places on a globe, given longitude and latitude
2. Make connection from Earth to Sun.
   • The Sun is described by longitude and latitude lines.
   • Introduce Carrington Rotation
     • A numbering of rotations starting from 1853.
3. Given a seven day sequence of EIT images, students plot two active areas on a solar grid.
   • A good set of data is that of Aug. 24 - 30, 1996, where two clear sets of solar activity are visible, one at -10 latitude and one at -30 latitude.
   • Once the seven images are retrieved print out the solar grid. Note that the grid has 36 divisions. (Remember the sun is spherical: 18 in front and 18 in back. Some are closer together than others, due to perspective, but all are equal.)
   • By holding the grid over the image up to the light, or on an overhead projector, students can mark sequential locations of these active regions.
     • For the -10 latitude active region, days 27-30, the spot has traveled 4/36 (1/9) of the distance around the sun in 3 days. Therefore its projected time of rotation at -10 latitude is 9x3 = 27 days.
     • For the -30 latitude region, from day 24 to day 29, the spot passes through 6/36 (1/6) of the solar sphere in 6 days Therefore its projected time of rotation at -30 latitude is 6x6 = 30 days.
4. Independent Student Research: Students study images of the sun for a period of 2 - 3 months, track active regions at different latitudes, and calculate differential rotations.

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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.