Page 26 - Curriculum Visions Dynamic Book

Because the photosphere is made of gas, it does not all spin at the same rate, just as our atmosphere does not spin at the same rate as the Earth. However, in the case of the Sun, where the temperature all over the surface is about the same, gases do not move between the equator and the poles as they do on Earth. Instead, bands of gas spin at differing rates depending on their latitude. Something similar also happens as thick layers of gases move on the gas giant planets such as Jupiter.
Gases spin fastest at the Sun’s equator, making a complete rotation every 25 days. At the poles gases spin more slowly, rotating every 36 days.
Superimposed on this latitudinal
spinning are vertical movements in and out
of the photosphere. They are convection currents, and they bring up hotter ionized gas, or plasma, from the lower regions of the photosphere and return cooler surface plasma (see page 22). This produces cells about a thousand kilometres across whose speckled surface effect is called granulation. Light areas are upwelling currents; dark granules are cooler, downward moving currents.
These cells form and re-form amazingly quickly. A cell might have a life of less than half an hour, and during this time gases move within the cell at up to 300 kilometres each second.
Sunspots
Although we see granulation all over the surface, what catches our attention when we see the Sun at lower magnification are larger features called sunspots. Sunspots were first seen in about a.d 1600.
convection currents
The circulating flow in a fluid (liquid or gas) that occurs when it is heated from below.
equator The ring drawn around a body midway between the poles.
granulation The speckled pattern we see in the Sun’s photosphere as a result of convectional overturning of gases.
ionized Matter that has been converted into small charged particles called ions.
latitude Angular distance north or south of the equator, measured through 90°.
penumbra The part of a sunspot surrounding the umbra.
plasma A collection of charged particles that behaves something like a gas. It can conduct an electric charge and be affected by magnetic fields.
pole The geographic pole is the place where a line drawn along the axis of rotation exits from a body’s surface.
sunspot A spiral of gas found on the Sun that is moving slowly upward, and that is cooler than the surrounding gas and so looks darker.
umbra The darkest region in the center of a sunspot.
 A closeup view of sunspots showing the umbra (very dark)
and penumbra (dark) among the granulations of the photosphere.
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