Heartbeat of the Sun

Our Sun is now coming down from its sunspot maximum. Its solar flares and sunspots are decreasing and its chromosphere is shrinking, but, it also means that the solar North-South magnetic field is increasing, and building up to its maximum. Our Sun's majestic heartbeat is twenty-two years. The recent maximum had two peaks, one in 2000 and the other in 2002.

Sol is the fiery, pulsating heart-centre of the solar system, which is something more than the burnt-out 'yellow dwarf' as astronomers regard it.  Just as cardiac fibre has a periodic contraction built into it, so likewise the Sun's surface has a self-reversing magnetic field within it, which flips over every eleven years. That is something very unearthly! The word 'plasma' refers both to the fluid of the bloodstream, and to the solar matter which streams out along with the solar wind, bathing the Earth.

At a sunspot maximum, the Sun's magnetic field becomes stretched out around its equator. It is in a highly stressed condition, so that sunspots are gradually pulled nearer to the solar equator by this stretching process. The magnetic-field tubes emerge through a sunspot, then re-enter the Sun by another. This field at the equator flips over at each sunspot minimum. In contrast, the solar magnetic field at its poles reverses at each sunspot maximum. Slowly, we begin to acquire a feeling for the heart-like functioning of that tremendous solar magnetosphere.

Early in 2001, NASA websites announced that the North-South magnetic field of the Sun was reversing its polarity, was flipping over, as it does every eleven years. This rhythm makes up the well-known 22-year cycle. Solar satellites recorded the event as it happened, making this the first time ever that the event was followed in real time. There are four stages in this cycle, just like there are in a heartbeat, and let's go over them. The North-South magnetic field emerges from its poles, reaching out above and below the ecliptic. As the solar equator is tilted merely six degrees to the ecliptic, this field is more or less perpendicular to it. It grows strongest as the sunspots are at their minimum  (the sunspots are then small, and there are only a few around the solar equator) and then grows weak as the sunspot maximum approaches - when, dramatically, it flips right over, between North and South, then starts increasing again with polarity reversed. Then as we saw, around the solar equator, the magnetic field becomes stretched-out and stressed at sunspot maximum, with strands threading in and out of the sunspots. Astronomers talk of a solar 'dynamo' as having a 'self-reversing magnetic field' and this is something unearthly - no magnetic field self-reverses here on Earth.

We are used to thinking of the 11-year sunspot cycle, but let's try instead to visualise two 22-year cycles, proceeding out of phase at the poles and equator. Thus the full solar heartbeat is a four-stage process, as might remind us of the human heartbeat. Between arteries and veins this goes through its four-stage systole-diastole process. Thus the emerging modern picture endorses Galileo's view of the Sun, that:
  

"...It is rather like the heart of an animal, in which

there is a continual regeneration of the vital spirits,

which sustain and give life to all its members." (2)

We experience the mean rotation period of the solar plasma (3) as 27.3 days, more or less. That is the mean rotation period of sunspots as we see them - and it also happens to be the lunar orbit period. If there are four plasma sectors, then this gives a change in sectors bathing the Earth, once a week. Thus Earth gets a fourfold experience of the Sun per sidereal lunar month! The polarity reverses, weekly. There are quite a lot of biological and climatological effects that result from this solar wind change.

The solar corona is far hotter than the Sun's surface, which has rather puzzled astronomers, rising to several millions of degrees in temperature. X-ray pictures of this solar corona are obtained from satellites. The corona streaming out far from the Sun is visible during a solar eclipse. Sunspots in contrast are cooler than their surroundings, making them darker.  Modern studies have come a long way towards a more biological image of our Sun. Even Eudoxos, who wrote:

"...Willingly would I burn to death like Phaeton, were this the price for reaching the Sun and learning its shape, its size and its substance."

might be pleased.