More about our sun

At According to Hoyt Stephanie Osborn continues her discussion of Solar, Space, and Geomagnetic Weather.

At the end of every 11-year cycle, the magnetic orientation of the spots…flips. Yeah, you heard right — this is one of the few times when the old trope about “reversing the polarity” is actually the correct answer. The end that was North becomes South, and the end that was South becomes North. MORE, the ENTIRE solar magnetic field ALSO flips! (This got very complex this last time; it wasn’t as fast and simple. It took nearly six months, and for a time our Sun had something like FOUR South poles, and NO North poles. Yeah, stellar magnetics gets crazy.) It takes a whole ‘nother cycle to get back to the way it started out. So that’s a second solar cycle, the 22-year cycle.

Now, sunspots look dark not because they’re cold, but because they’re just a bit cooler than the surrounding plasma of the photosphere (which is the visible “surface” of the Sun). If the photosphere is about 5,800°K (~10,500°F), then the sunspots are about 3,000-4,500°K (4,900-7,600°F). Still plenty hot enough to fry your bacon, but still several thousand degrees cooler than their surroundings. They can be teeny-tiny (relatively speaking, of course) or they can be huge things (80,000km/50,000mi — not too shabby when you consider the Earth is about 13,000km/8,000mi diameter), big enough to be seen by the naked eye. (But don’t do that — we like having eyesight. If you really want to observe the Sun, the best way is to get a telescope, aim it at the Sun, and hold a sheet of white cardboard behind the eyepiece. Adjust the distance until you get an image of the Sun projected on the cardboard. This is a cool way to watch solar eclipses, too. If you don’t have a telescope, grab a shoebox, punch a small hole in one end, turn it upside down and point the hole at the Sun, then tilt the thing around until you get a small image inside the opposite end of the box.) Sunspots aren’t really dark at all; they just APPEAR dark because of the contrast with the surrounding hotter, brighter photosphere.

Read more here.

Solar, Space, and Geomagnetic Weather

Stephanie Osborne explains,

[This is a basic image of the Sun, complete with sunspots. The small black circle in the top right edge of the solar disk is actually Venus beginning a “transit” (passage) between us and the Sun.]

All three — solar weather, space weather, and geomagnetic weather — are interconnected. This is because the Sun has a magnetic field that extends far past the Earth, and so the Earth’s magnetic field interacts with it. “Space Weather” is essentially a term for the conditions of space in the general vicinity of Earth, but not necessarily inside the Earth’s magnetic field.

We are also sitting inside the atmosphere of the Sun, the corona. The corona is a plasma — a gas composed of charged particles, mostly protons and electrons, with some neutrons and assorted atomic nuclei (such as alpha particles — helium nuclei) thrown in for good measure. Its temperature is around a 1,400,000°-1,600,000°Kelvin, or about 2,500,000-2,900,000°F. It has a density that ranges about 5-10 particles per cubic centimeter, and it is generally moving away from the Sun, “evaporating” under the influence of the powerful solar magnetic fields.

This generates a kind of wind, usually coming out from the Sun and spiraling away — yeah, the “solar wind.” Granted, the corona isn’t very dense, but it’s dense enough to create some effects, and we’re working on using it to our benefit, like in solar sails and such, which can use the solar wind as much as light pressure to maneuver around the Solar System like a spaceborne version of the clipper ships of old. (But that’s a different blog post.) Solar wind speeds range from 400-750km/s (895,000-1,700,000mph), and under certain conditions, can get much, much faster.

...The solar magnetic field can look like this:


Now, see all those places where the magnetic field lines are going off into space, instead of looping back around to the “surface”? Those are shooting all that plasma off into space, ALONG THOSE LINES, and the result, when you look at it with the right frequency light and equipment, is what’s called a coronal hole. Looking at ‘em the right way, it looks like this:

Read more here.