Above are two examples of an (Continuum, left) and an “I-gram” “M-gram” (Magnetogram, right) obtained with the MDI instrument on the SOHO spacecraft. The or is a conventional, visible-light view of the Sun’s photosphere “intensity-gram,” and sunspots. The M-gram, or reveals the of magnetic fields polarity “magneto-gram,” on the photosphere—white and black indicate N and S magnetic polarity. Both types of data show different characteristics of the same thing: magnetically active regions on the photosphere. While the I-gram is a direct, visible light image of the photosphere, the magnetic polarities shown in the M-gram are derived from measurements of in the light emitted by gases embedded in the magnetic polarization fields. Either of these types of images can be used in this activity to determine the rotation of the Sun. Measuring Solar Rotation—Solar Latitude/Longitude Method What you will do You will make a more refined measurement of the Sun’s period of rotation by measuring the Sun’s angular velocity. How you will do it You will use SOHO MDI I-gram or M-gram solar images and a specially plotted, transparent latitude/longitude grid called a Stonyhurst Disk (see example below) to track the motion of sunspots in terms of degrees of longitude. From this angular motion measurement, you will calculate the spot’s angular velocity, and from that result the rotation period of the Sun. Materials and Skills Printed out full-disk images of the Sun on different dates—SOHO MDI or M-grams recommended: Properly scaled transparency copy of a date-appropriate Stonyhurst disk (see Appendix on page 84) Sunspot Latitude/Longitude Tracking Log (page 31) Angular Velocity and Solar Rotation Period Worksheet (page 32) Familiarity with latitude and longitude and the geometry of a sphere Basic math skills: ratios, units of physical quantities Background The method for measuring solar rotation in the previous activity makes the assumption that we view the Sun from a point in space directly over the Sun’s equator, which gives
Above are two examples of an “I-gram” (Continuum, left) and an “M-gram” (Magnetogram, right) obtained with the MDI instrument on the SOHO spacecraft. The or “intensity-gram,” is a conventional, visible-light view of the Sun’s photosphere and sunspots. The M-gram, or “magneto-gram,” reveals the polarity of magnetic fields on the photosphere—white and black indicate N and S magnetic polarity. Both types of data show different characteristics of the same thing: magnetically active regions on the photosphere. While the I-gram is a direct, visible light image of the photosphere, the magnetic polarities shown in the M-gram are derived from measurements of polarization in the light emitted by gases embedded in the magnetic fields. Either of these types of images can be used in this activity to determine the rotation of the Sun. Measuring Solar Rotation—Solar Latitude/Longitude Method What you will do You will make a more refined measurement of the Sun’s period of rotation by measuring the Sun’s angular velocity. How you will do it You will use SOHO MDI I-gram or M-gram solar images and a specially plotted, transparent latitude/longitude grid called a Stonyhurst Disk (see example below) to track the motion of sunspots in terms of degrees of longitude. From this angular motion measurement, you will calculate the spot’s angular velocity, and from that result the rotation period of the Sun. Materials and Skills Printed out full-disk images of the Sun on different dates—SOHO MDI or M-grams recommended: Properly scaled transparency copy of a date-appropriate Stonyhurst disk (see Appendix on page 84) Sunspot Latitude/Longitude Tracking Log (page 31) Angular Velocity and Solar Rotation Period Worksheet (page 32) Familiarity with latitude and longitude and the geometry of a sphere Basic math skills: ratios, units of physical quantities Background The method for measuring solar rotation in the previous activity makes the assumption that we view the Sun from a point in space directly over the Sun’s equator, which gives
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