Contains:  Solar system body or event
Calculations, Steve Lantz

Calculations

Acquisition type: Drawing/Sketch
Calculations, Steve Lantz

Calculations

Acquisition type: Drawing/Sketch

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Description

This is an animation of my images for the track of sunspot AR2833 as it moved across the solar disk. As an adjunct, I performed calculations to determine the sidereal solar rotation period at 22 degrees north latitude (solar coord), which what is shown in the original panel. This is a geometric approach in which the original composite image of all of the sunspots is the starting point. A copy of this image is made as a blank disk for the purpose of mapping the equatorial view of the composite image onto a polar view of the sun (N is up). Central angles for the sunspots' motions can then be measured (three were used in the analysis). For each angle, the time span between positions can be determined from the time stamps of the images. This allows a proportion to be set up that has days per central angle equals ? per 360 degrees, in which ? is the period of a full rotation with respect to the distant stars (sidereal period). However, the central angles in the diagram are actually synodic values because the earth is revolving around the sun. A correction is needed to change the results from the diagram -- synodic values -- to sidereal values, which is accomplished by the formula as shown. At the latitude of the sunspot track, the literature value is around 26 days per sidereal rotation. My result is 28 days +/- 3 days, so at least the accepted value lies within the margin of error. The sun exhibits differential rotation, that is, the gases in the sun rotate fastest at the equator, with a period of 25 days, and slowest near the poles, where the rotational periods are in the low 30's of days. The other issue here is the earth's spin axis is tilted with respect to its orbital plane by 23.5 degrees. The sun's spin axis is tilted by 7 degrees with respect to this plane. Moreover, the sun's spin axis points in a different direction than the earth's. Thus, most of the time we are not looking directly at the sun's equator. By pure serendipity, though, it just so happens that in June all of the geometries work out to give a true equatorial view of the sun. Some of my data were acquired in later June, and there may be some error associated with the view moving away from truly equatorial near the end of the month.

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  • Calculations, Steve Lantz
    Original
  • Final
    Calculations, Steve Lantz
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Description: This is the animation that shows sunspot AR2833 moving across the solar disk due the sun's rotation. Other than between the first and second frames (separated by two days) the frames are one day apart (three frames were synthesized using WinJupos to make this possible). It gives us an idea of how a sunspot moves from day to day.

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Calculations, Steve Lantz