Re: Quiet Sun


"Brian Tung" <brian@xxxxxxx> wrote in message
news:dtiqtt$ek$1@xxxxxxxxxxxxxxxxxxx
Chu Mai Wang wrote:
I have wondered if the technology for sunspot detection just wasn't good
enough during that period. What were the best telescopes of the time?
Did they just project the suns image onto paper to see sunspots or did
they have sun filters then?

They didn't have solar filters. They either used solar projection or,
in a few cases, they may even have looked directly at the Sun near
sunrise or sunset. Not a good tactic. (This means you!)

It is true that sunspot records were considerably more sporadic than
they are today, so that if they were all we had to go on, we would
indeed consider the evidence suggestive but inconclusive. As it
happens, however, there is some independent evidence for the Maunder
Minimum and other extended solar minima. If I recall correctly, solar
minima and maxima are correlated, even when the cycle is active, with an
increased solar magnetic field, which acts to partly shield the Earth
from cosmic rays.

The most numerous of these cosmic rays are protons. Now, when protons
make it into the atmosphere, they occasionally start a burst of
secondary radiation, of which some are speeding neutrons (which would
not be deflected by the solar magnetic field, incidentally). Some of
those neutrons encounter a nucleus of nitrogen-14, the most common atom
in the atmosphere. When they do, they typically dislodge and replace a
proton, converting the nitrogen-14 into carbon-14.

Carbon-14, as you probably know, is not stable. It is radioactive, with
a half-life of about 5,700 years. (For those more used to exponential
formulations, that means it has a mean life of about 8,200 years.) As
a result, even as cosmic rays are converting N-14 into C-14, beta decay
is converting the C-14 back into N-14, and in this way, an equilibrium
is maintained. At any time, there are about a trillion C-12--the most
common isotope--atoms for every C-14 atom. Sounds tiny, but it still
means that a typical air balloon (not helium) containing, oh, let's
say 22.4 liters of air, has about a quarter of a billion C-14 atoms.

As long as an organism is living, it exchanges carbon atoms with the
surrounding environment, and so its C-14 to C-12 ratio remains at about
one in a trillion. As soon as it dies, however, it ceases to take in
carbon, and C-14 begins a long slide toward zero. This is the basis for
radiocarbon dating.

The significance of this for the Maunder Minimum is that we can look
at tree rings and determine which rings fall in the Maunder Minimum,
and figure out what the C-14 levels were at that time. They appear to
be consistently high during that time (as David mentioned, around 1645
to 1715, roughly coincident with the reign of the Sun King, ironically
enough [1]), which is consistent with elevated levels of cosmic rays,
and therefore with reduced solar activity.

In this way, other minima have been tentatively identified, some of
which predate any possible sunspot record, and which range in duration
from decades to centuries. They seem to come at random intervals with
no obvious pattern. If these minima are real, what causes them? Nobody
knows for sure.


And that just about winds up todays archeology 321 lecture. Here..comes,
the Sun King...everybodies laughing, everybodies happy....


.

Relevant Pages

  • Re: Quiet Sun
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