The Sun, 25 October 2013!The difficulties in finding out how the sun works are different than those in 1.any other part of astronomy: it is too bright. !Everything else is too far and faint.!A.There is usually a social division in astronomy departments between solar B.astronomers and other astronomers: !Their schedules are different. !a.Solar astronomers work during the day instead of the night. !1.They don't use the same equipment. !b.If you point any non-solar telescope at the sun, the components melt 1.from all the energy they are absorbing. !Instruments for observing the sun are designed differently than A.telescopes. !The sun is a star located in the middle of our solar system: !2.This fundamental trait was suspected in the 1600s, but not proven until the A.1800s. !It still isn't being taught in some elementary school classrooms.!B.You can look at the sun in many ways, including in hydrogen alpha, helium, x-3.rays, magnetic fields, and ultraviolet light. The sun looks different and tells you different information depending on what instrument you use to look at it.!Since the 1960s, astronomers have been able to observe the sun in A.ultraviolet light.!Since the 1970s astronomers have been able to observe the sun in x-rays, B.which looks dramatically different from the sun in visible light. !The surface of the sun appears black in x-rays.!a.The reason is that the x-rays are generated in temperatures above a 1.million degrees kelvin, but the surface of the sun is only 6000 degrees kelvin. The sun's surface is too cool to generate x-rays. !X-rays are generated in the sun's atmosphere (corona), where 2.temperatures can occasionally reach up to 3 million degrees. !The temperature of the sun's atmosphere is usually around 1 A.million. !Most x-rays come from the areas of the sun with the most sunspots, two b.belts on either side of the equator. !This is also true for magnetic fields and radio energy.!1.Though astronomer's images of the sun in x-rays have gotten sharper, no c.one understands why they are generated. This is because no one knows why the sun's corona is millions of degrees kelvin when it must gain energy from the sun's 6000 degrees kelvin surface.!This is a major, long term puzzle.!1.If you look at the sun in radio waves, you can make out the sun spot groups C.and some energy coming from the rest of the sun.!When you look at the sun in a narrow spectral wavelength of hydrogen, D.you can see detail on the sun's surface that seems to be influenced by magnetic fields.!Spicules are a phenomena on the sun that looks like brush strokes a.following magnetic fields.!The spectra of parts of the sun also shows evidence of magnetic fields b.(some lines are double or tripled). !Some places do not have these lines, suggesting there are only strong 1.local magnetic fields on the sun, not a unified, global magnetic field!The only sure way to detect magnetic fields is to send and instrument c.into them, but the sun's energy would melt any device before it got close enough.!Magnetic fields on the sun, like magnetic fields elsewhere, are not d.understood.!Any student who solves this problem to the satisfaction of experts in 1.the specialty, gets an instant A for the entire course, regardless of anything else. !Sun spots:!4.Sun spots usually come in groups with a leading large spot, a trailing large A.spot and a bunch of smaller spots in between. !There is a less dark area around each sun spot.!B.Every sun spot group has a magnetic field associated with it, but there are C.also magnetic fields in places without sun spot groups. !The sun spot cycle: !D.Most pictures of the sun in textbook show the sun with a lot of sun a.spots, though in reality the quantity of sun spots changes: !They change a little each day, substantially every weak and hugely over 1.several years. !The largest sunspot group photographed was on March 9, 1947. !2.It was half a degree across – big enough for the naked eye to A.distinguish (with the appropriate filter).!Never look at the sun directly, sunlight can burn cells in your a.retina without you feeling it. !The amount of radiation that the sun gives off in radio and other b.wavelengths changes during the sun spot cycle. !In these wavelengths, the sun is at its brightest during the sun spot 1.cycle's maximum.!In visible light, however, the sun stays nearly the same brightness all 2.the time.!Astronomers have carefully notated the quantity of spots visible for a c.long time, and discovered that there is a rough cycle: !The average length of a cycle is 11.1 years from peak to peak (as 1.short as 8 years and as long as 14 years).!Sun spots change polarity every cycle:!2.If the current cycle has north seeking spot groups in the northern A.hemisphere, the next cycle will have south seeking spot groups in the northern hemisphere. !The sunspot cycle is technically 22 years long, not 11 years. !1.No one understands this: !2.Any student who solves this problem to the satisfaction of A.experts in the specialty, gets an instant A for the entire course, regardless of anything else.!If you graph the distance between sunspots and the sun's equator over a d.cycle, the resulting graph looks like a butterfly (it is called a butterfly diagram). !When a sun spot cycle is new, the spots in it occur roughly 20 1.degrees north or south of the equator of the sun. !Within a year, these spots are 40 degrees away from the equator. !2.As the sun spot cycle continues, the spots approach the equator again. !3.Any student who solves this problem to the satisfaction of experts in 4.the specialty, gets an instant A for the entire course, regardless of anything else!Some sun spot cycles are more active than others, so a sun spot cycle is e.matter of relative numbers rather than absolute numbers.!There was a long period with very few sunspots from 1650-1700 1.called the "Maunder minimum," as it was discovered by someone named Maunder. No one knows why this was.!Any student who solves this problem to the satisfaction of experts A.in the specialty, gets an instant A for the entire course, regardless of anything else. !There are currently quite a few more sunspots, and no one knows 2.why.!Any student who solves this problem to the satisfaction of experts A.in the specialty, gets an instant A for the entire course, regardless of anything else.!Solar Flares: !5.These occur when a part of the sun less than the size of a sunspot group A.suddenly becomes much brighter than everything around it for
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