1. Solar Rotation Lab 3

2. Differential Rotation The sun lacks a fixed rotation rate Since it is composed of a gaseous plasma, the rate of rotation is fastest at the equator (24 days), and decreases as latitude increases (30 days at polar regions) ~27 days

3. Sidereal Rotation At the equator the solar rotation period is 25.38 days and is called the sidereal rotation period Sidereal rotation period – time it takes to rotate 360 degrees on its axis Not to be confused with synodic rotation

4. Synodic Rotation Sun has a synodic rotation period of 27.2753 days, which is the time for a fixed feature on the sun to rotate to the same apparent position as viewed from earth The synodic period is longer because the sun must rotate for a sidereal period plus an extra amount due to the orbital motion of the earth around the sun

5. Use of Tracers to Measure Rotation Sunspots are used as tracers to measure rotation rates of Sun A tracer is a fixed feature on the Sun Sunspots had been observed since ancient times, but after Lipperhey/Galileo invented the telescope it was seen that they turn with the Sun, and thus could define the period of the solar rotation

6. Sunspots magnetic elements Every ~11 years the number of sunspots seen on the Sun increases from ~0 to ~100, then decreases to ~0 again as the next cycle starts The polarity is reversed also So a complete sunspot cycle is ~22 years Seen in a band, 5-40˚ latitude above and below the solar equator

7. What are Sunspots? Sunspots appear as dark spots on the surface of the Sun Sunspots are magnetic regions on the Sun with magnetic field strengths thousands of times stronger than the Earth's magnetic field Temperatures in the dark centers of sunspots drop to about 3700 K (compared to 5700 K for the surrounding photosphere) They typically last for several days, although very large ones may live for several weeks Sunspots usually come in groups with two sets of spots. One set will have positive or north magnetic field while the other set will have negative or south magnetic field The field is strongest in the darker parts of the sunspots (umbra), and weaker and more horizontal in the lighter part (penumbra)

8. Sunspots

10. Solar Magnetic Field The Sun’s magnetic field is produced by the flow of electrically charged ions and electrons Sunspots are places where very intense magnetic lines of force break through the Sun's surface The sunspot cycle results from the recycling of magnetic fields by the flow of material in the interior The prominences seen floating above the surface of the Sun are supported, and threaded through, with magnetic fields The streamers and loops seen in the corona are shaped by magnetic fields Magnetic fields are at the root of virtually all of the features seen on and above the Sun

11. X-ray image of the sun (corona)

12. Corona The Sun's outer atmosphere (corona) is hotter than 1,000,000ºC Usually temperatures fall as distance increases from a heat source This is true in the Sun's interior right up to the visible surface BUT THEN, over a relatively small distance, the temperature suddenly rises to extremely high values Areas on the Sun near sunspots often flare up, heating material to millions of degrees in just seconds (solar flares) and blasting billions of tons of material into space (coronal mass ejections)

13. Other features of the Sun - Faculae Faculae are bright areas that are usually most easily seen near the limb, or edge, of the solar disk These are also magnetic areas but the magnetic field is concentrated in much smaller bundles than in sunspots While the sunspots tend to make the Sun look darker, the faculae make it look brighter

14. Faculae

15. Other features of the Sun - Granules Granules are small (~1000 km across) cellular features that cover the entire Sun (except for those areas covered by sunspots) They are the tops of convection cells, where hot fluid rises up from the interior in the bright areas, spreads out across the surface, cools, and then sinks inward along the dark lanes Individual granules last for only ~20 minutes The granulation pattern continually evolves, old granules get pushed aside by new emerging ones The flow within the granules can reach supersonic speeds of more than 15,000 mph and produce sonic "booms" on the Sun's surface

16. Granules Movie - http://science.nasa.gov/ssl/pad/solar/feature1.htm http://science.nasa.gov/ssl/pad/solar/feature1.htm

17. Other features of the Sun - Supergranules Supergranules are much larger versions of granules (~35,000 km across) These features also cover the entire Sun and continually evolve Individual supergranules last for ~1-2 days and have flow speeds of ~1000 mph The fluid flows observed in supergranules carry magnetic field bundles to the edges of the cells where they produce the chromospheric network

18. Supergranules

19. Other Features of the Sun - Chromospheric Network

20. Other Features of the Sun - Filaments and Plages

21. Other Features of the Sun - Prominences

22. Prominence eruption http://science.nasa.gov/ssl/pad/solar/imag es/granddaddy.mpghttp://science.nasa.gov/ssl/pad/solar/imag es/granddaddy.mpg

23. Other Features of the Sun - Spicules

24. Magnetosphere

25. Solar Wind The Sun is the source of the solar wind; a flow of gases from the Sun that streams past the Earth at speeds of more than a million miles per hour Disturbances in the solar wind shake the Earth's magnetic field and pump energy into the radiation belts Solar flares and give off ultraviolet light and x- rays that heat up the Earth's upper atmosphere