Q: I'm still really confused about Neutrinos. I understand that they're
subatomic particles that can travel through anything. But how are they
released from the Sun (I understand it has something to do with converting
Hydrogen atoms)? And if they have no electric charge or mass, how were
they
found? And if scientists are indeed still baffled by their properties
how
can they be sure that ANY of the observations they've made on the sun
(such
as the correlation between Neutrinos and the conversion of Hydrogen)
are
correct? Please help explain this concept, as the book seems pretty
muddled
on it and Prof. Basri hasn't really covered this topic yet! Thanks!
*A: Scientists first theorized the existence of neutrinos because
when considering the proton-proton cycle, not enough energy was released
to
account for the mass-energy difference between the hydrogen and helium.
In order for total mass-energy to be conserved, some other particle
had to
exist as a by-product of the reaction, carrying energy away.
Scientists attempted to detect neutrinos by building a lab deep underground.
They filled a vat with cleaning fluid, of all things. The cleaning
fluid
contained a lot of chlorine. Now it was build deep underground
so that
no particles or radiation could get through and interact with the fluid.
When neutrinos encounter chlorine atoms, there's a very small probability
they will interact with chlorine and change it into argon. They
knew, based
on calculations, how many neutrinos should pass through the cleaning
fluid
per day, and the probability of any given neutrino making an argon
atom, so
they were able to predict the rate of creation of argon atoms.
However,
when they did the experiment, they got a rate of about 1/3 of what
they were
expecting. (The fault was not with their equipment. It
was sensitive
enough, and several scientists have repeated the experiment with the
same results.)
The current best theory to explain the solar neutrino problem (as this
strange result has come to be known) is that neutrinos must change
from one
kind to another. There are three kinds of neutrinos known about,
but only
one kind which turns chlorine into argon. This is a much more
likely
solution than to assume that all of our understanding of fusion reactions
in the sun
is wrong.
Q: Why is the photosphere what we see as the surface? How do we see
a
surface of gas anyways, and isn't the chromosphere also gas, and at
even a
higher temperature? That is, what's the difference?
*A: The gas in the photosphere is very dense. The gas in the chromosphere
is not. However, if we were to get close to the sun, the surface
wouldn't
appear to be absolutely crisp.
Q: Why is the corona even hotter than the chromosphere?
*A: The long answer is way to complicated to get into here. The
short
answer is just to say that it has to do with magnetic disturbances
depositing
energy in the corona. Although the details aren't exactly understood,
it
seems that as the density of the gas decreases, the hotter it gets
as
a magnetic wave passes through it. Since the corona is less dense
than
the chromosphere, it heats up more.
Q: My question is how are sun protrusions out of the sun spots produced?
A: The sun is hot enough to ionize particles. In other words,
the atoms
are hot enough (have enough energy) that the electrons get stripped
away
from protons. Both electrons and protons are charged. Charged
particles
are attracted to magnetic fields, and strong magnetic fields emanate
from
sunspots.
Q: What are cosmic rays? Is it some kind of light spectrum?
*A: Cosmic rays are exremely energetic particles. They can be
electrons,
positrons, protons, even nuclei (protons and neutrons bound together.
Some come from stars like the sun, but most are believed to originate
in
things like supernova explosions (which will be discussed in a few
weeks).
Q: are magnetic waves the only reasons why the chromosphere and corona
are
heated?
A: In the lower chromosphere, acoustic waves (noise) also plays
a role, but mainly
the answer is "yes"
Q: How do the magnetic fields on sun cause sunspots?
A: The sun surface of the sun is heated, primarily, by convection.
In other
words, blobs of hot material from deep within the sun rise upward,
deposit
their energy and heat, then sink back down. The magnetic fields
in the
sunspots repel these hot blobs and redirect them away from the sunspot.
Hence the sunspots are cooler.
Q: Do we know that the sun is at the half way mark of its life, or do
we
just think that it will live to be 9 Billion yrs. old and we are assuming
that
its 4.5 Billion yrs. old already?
*A: We know the Earth is 4.5 billion years old from radioactive dating,
and
it's safe to assume the sun and the Earth formed at the same time.
Q: i read the part about neutrinos and positrons a couple of
times...but it still was not clear to me what their significance was.
*A: As stated above, neutrinos are needed to carry off excess energy
released by the proton-proton chain. Positrons are created in
order to conserve
charge. (You start with 4 protons (which each have a positive charge)
and wind up
with helium (which has 2 positive charges) and thus you need 2 positrons
to carry
off the other 2 positive charges.
Q: What functions do prominences provide for the sun?
A: I'm not sure I understand this question. Prominences occur
when
strong magnetic fields occur near the surface of the sun and ionized
particles (protons and electrons) are attracted to these curved magnetic
fields.
Q: I was wondering if you could explain more clearly what a "hydrostatic
balance" is.
A: If you heat up a gas it will expand and become less dense.
(This is how
hot air balloons work). Imagine you were to take an ordinary
party balloon,
and somehow cast a magic spell on it so the rubber would never break.
Then
put the balloon over an open flame. The balloon would get bigger
as the gas
inside heated up and expanded.
Well, the sun is made of hot gas, which means it wants to expand.
However,
the sun is also very massive, which means it wants to collapse under
its own
gravitational pull.
The fact that the sun is in hydrostatic balance means that the sun is
the
exact right size now that it wants to shrink under its gravity exactly
as much as
it wants to expand because it's a hot gas. This is what we mean
when we say
pressure balances gravity.
Q: Are electromagnetic fields particles, or heat or light? What do they
consist
of?
*A: An electromagnetic field is not actually composed of anything physical.
It is merely a force field, like a gravitational field is. So
what's a force
field (get rid of any images in your head of what they lock the
brig with in Star
Trek)? Let's talk about a gravitational field first, since this is
something we're
a little more familiar with in our everyday lives. Objects which
have mass
possess gravitational fields, the more the mass the greater the field.
When you
place another object which has mass in the gravitational field of the
first
object, a graviational force will push or pull on the second object.
For instance,
if you place a wrench a meter off of the floor and let go, the gravitational
force exerted on it will cause it to fall toward the Earth. How
do we calculate
how powerful the gravitational force is? We calculate the strength
of the
gravitational field one meter above the surface of the Earth.
Similarly, imagine an object with an electromagnetic field. (Objects
which
have moving charged particles in them generate electromagnetic fields.)
If you
place a charged particle (electron or proton, for instance) in that
field it will
move according to the force exerted on it by the electromagnetic field.
So how, you ask, does an object with an electromagnetic field "communicate"
with the electron near to it in order to push or pull that electron
with its
electromagnetic force? That's a darn good question! Physicists
refer to
weird particles that are called 'virtual photons' as an explanation,
but I'm not
even sure how that's supposed to work. This stuff is WAY beyond
the scope of
this course.
Q: In the chapter about the sun, how does the cooling gas get trapped
in
the magnetic field?
A: The gas contains a lot of ionized charged particles (electrons and
protons). In other words, some of the neutral hydrogen atoms (a proton
+ an electron)
got hot enough that the electron and proton flew apart. Charged
particles are
attracted by magnetic fields, so when you have a strong magnetic field
loop
near the surface of the sun, the ionized particles get trapped in it
and you
can get a prominence.
Q: -how does the number of sunspots on the sun affect the surface
temperatures on the earth?
A: This is a very good question, and one that does not have a concrete
answer yet. All that was known for a long time was that certain climatic
changes
correlated to the sunspot cycle. (Now correlation shouldn't always
be taken to mean
that there is a cause and effect relationship. Just because two
things are correlated,
doesn't mean one causes the other. For example, there are many
other things
which seem to be correlated to the 11-year sunspot cycle -- certain
stock values,
Beatles popularity, and skirt lengths popular in fashion. Does
the sunspot
cycle really make us like shorter skirts one year and longer ones the
next?
Probably not.
This is common mistake in logical thinking. Listen to one of the
presidential candidate's speeches sometime. Chances are he'll
use this kind of flawed
logic to come to some conclusion based on correlated trends.
However, the
correlation between sunspots and climate goes back so far (at least
back to the 1600's)
that we think that there probably IS a cause and effect relationship,
and that
it's not just a coincidence.)
There is now at least a partial theory as to why sunspot number and
climate
changes may be correlated. When the sun has a lot of sunspots,
it's going
through a magnetically active period, and thus spewing out a lot of
solar
wind at the same time. (Solar wind is made of protons and electrons).
It is
this solar wind which somehow can alter weather on the Earth, perhaps.
However,
the exact nature of how the solar wind could affect weather is quite
a
mystery, and not yet understood by scientists.
Q: More explanation on the proton-proton chain.
A: The proton-proton chain is the name given to the nuclear process
that
powers the sun. It is a process of nuclear fusion, i.e. you star
with more than
one nucleus which fuse into one nucleus, giving off energy. In
this case you
start with two hydrogen nuclei, i.e. two protons. When these
two fuse
together, one of them turns into a neutron, you get a different kind
of hydrogen
nucleus - one with a proton AND a neutron (remember it is the number
of protons which
determines which element you have). A positron is given off to
conserve
charge. (You start with two positive charges, then you end with two
postive charges.
A neutrino and energy (in the form of a photon) are also given off
as
by-products of the fusion. So the first step in the proton-proton
chain is:
p + p -> d + e+ + neutrino + energy
(The d stands for a deuteron, which is the name to the funky hydrogen
nucleus which has a neutron.)
In the next step the deuteron (proton+neutron) fuses with another proton,
and you wind up with a helium-3 nucleus (2 protons + 1 neutron) and
some energy
released.
p + d -> 3He + energy
Now helium likes having 2 neutrons instead of just 1, so there's one
more
step. Two helium-3 nuclei fuse together, but two of the protons are
spewed off,
leaving a nice, stable helium-4 nucleus (2 protons + 2 neutrons), along
with the two
protons and some energy as by-products:
3He + 3He -> 4He + p + p + energy.
This is quite a nice way to generate energy! So why don't we do
it on
Earth?
The answer is that you need to have your hydrogen REALLY REALLY HOT!
Protons have positive charges, and two objects with the same charge
repel one
another. You must have the protons moving REALLY fast in order for
them to bonk into
one another and fuse before they fly away from each other, repelled.
The only way to accelerate the protons to these high speeds is to heat
the
gas.
Think of it like this. Imagine a party filled with people having
terrible
body odor. As soon as two people get close to one another, they are
repelled. Now
imagine getting them really drunk. They start running madly about
the room. If two
of them are running fast enough they may collide, despite their repelling
odor. When they get close enough, each may realize that Golly! the
other one's
pretty attractive! So they connect physically and energy is released.
These temperatures which allow fusion to occur are at about one million
degrees, a temperature very difficult to generate on the Earth.
This is why we don't
have Mr. Fusion car batteries like in Back to the Future.
Q: Can you elucidate how magnetic activity affects solar
activity?
A: Much of the surface of the sun is composed of charged particles which
react strongly to magetic fields.
Q: Here's my little Q. It kind of applies to the Sun but not really.
On a
local College Station where I live (Hayward) there's an
Astro professor who has
televised lectures. In discussing the solar system, he mentioned the
possibility of a dead star (black dwarf?) in our system that has long
since
burned out. Is this speculation in the Astronomy community? A fact?
Did I
misinterpret what he was saying? Or is he full of crapola?
*A: I believe that you were hearing about the Nemesis theory.
Controversial
fossil evidence exists which may point to the conclusion that there
are mass
extinctions on Earth about every 26 million years. One theory
which arose
to attempt to explain the apparent regularity of the mass extinctions
is the
Nemesis theory.
Nemesis was the name given to a hypothetical black dwarf orbiting the
sun
in an eccentric orbit. (A black dwarf is a burned-out white dwarf,
no
longer glowing, and thus very difficult to see. We'll talk about
such things soon
in the course). The theory said that every 26 million years Nemesis
would
swing close enough to the Oort cloud to gravitationally perturb the
orbits
of a lot of comets, sending them hurtling toward the inner part of
the solar
system. Some of these comets would then impact into the Earth,
causing mass
extinctions, ala the dinosaurs.
However, most scientists now agree that this hypothesis is false, and
that
we would be able to detect, by other means, such a black dwarf so close
to the
sun.
Q: I was curious about sunspots- I know that they are darker and
cooler spots that contain strong magnetic fields, but are there any
other
uses or characteristics about them (i.e. do they change
anything but the sun's appearance, affect anything else....)?
A: Not really. You seem to have the important things down.
The only think
I can think of to add is that they tend to appear in pairs, which
is related
to the fact that they have strong magnetic fields. This is because
each of
a pair of sunspots lies at the base of a magnetic field line looping
up out
of the surface of the sun.
Q: Can you please go over how the ideal gas law works?
A: The ideal gas law says that the pressure of a gas times the volume
of
that gas are directly proportional to the temperature of the gas:
P*V is proportional to T
Example: Imagine you have an indestructable balloon, and you double
the
temperature of the gas inside. Assuming the pressure stays the
same, the
volume of the balloon must then double.
On the other hand, imagine a glass jar filled with gas, and you double
the
temperature of the gas. Assuming the jar stays the same size,
the pressure
of the gas inside the jar would double.
Finally, imagine a jar filled with gas, and you put a leak-proof piston
into
the jar, halving the volume. Assuming temperature stays the same,
pressure will
double.
Q: What causes the ganulation of the sun? What is it so dark?
A: Granulation is caused by the fact that the surface of the sun is
heated
by convection -- hot bubbles from deep within the sun rise to the surface,
release their heat and energy. Then the cool blob sinks back
down. When the blob
first gets to the surface, it's hot and therefore bright. When
it's released its
energy and is about to sink back down it's cooler and therefore dimmer.
Q: For chapter 11, can you explain more about the aurora.
I have heard the explanation more than once, but I am
still confused about it.
A: As stated somewhere above, the sun constantly spews out a solar wind
composed of charged particles (protons and electrons). When these
charged
particles get close to the Earth, Earth's magnetic field steers them
either
toward the north or south pole. When these particles then enter
the
atmosphere, they do so at very high speed (they're very energetic particles).
When
they're in the atmosphere, they interact with molecules in the air,
causing them to
be excited to higher energy states. When the molecules drop back
down to
lower energy states, they emit photons. We see these photons
as pretty aurorae.
Q: And regarding the sun, how many of the sun's characteristics can
you
change (mass, temperature, strength of magnetic field, etc.) and still
keep a
planet like the earth conducive for life? In other words, assuming
you have a
planet with the proper raw materials (like water and the right atmosphere)
at the proper distance, could life still spring up if that planet orbited,
say,
a red giant?
A: We believe that the prime ingredient for the creation of life is
the
presense of liquid water. As long as climatic conditions were
such that the water is
liquid, there seems to be a good possibility that life may develop.
So, in
4.5 billion years when the sun swells to a red giant and Earth gets
fried, maybe
the surface of Europa will melt and life will develop there.
On the other
hand, the red giant phase is much shorter than the main sequence
(hydrogen-burning) phase, so the life probably won't have time
to evolve into anything
intelligent (assuming it takes billions of years to evolve to
intelligence as in the
case with humans.)
Q: How is it that the sun is powered by its gravity?
A: It is not, at least directly. The fact that it is massive,
means that it
has a lot of self-gravity, which means that the pressure in the core
of the
sun is quite high, which means that the temperature is quite high.
It is the
high temperature that allows nuclear fusion to occur, and it is this
nuclear
fusion which powers the sun.
Q: When they say that, for example, the sun at the equator has to move
faster than say at the poles to keep up and make the full rotation,
what
exactly has to move faster? is it just the surface?
A: The sun's equator does not only move fast enough to 'keep up' with
the
poles, but it in fact moves faster!
Consider the Earth. If you live on the equator, over the course
of a day
(one rotation period), you trace out a distance equal to the circumference
of the Earth, 40000 km. If you live 1 kilometer away from
the north pole, the
Earth's rotation only takes you through a circular path of 2*pi, or
about 6 km, over
the course of one day. Velocity = distance over time. In
order to cover
the much greater distance at the equator during the same 24 hours,
you must
be moving much faster at the equator.
The above paragraph about the Earth is true because it rotates as one
solid
body. The time it takes for an object at the equator to complete
one
rotation equals the time it takes for an object at the poles to complete
one
rotation.
For the sun, the equator completes one rotation QUICKER than the poles
complete a rotation. Look at figure 11.23 on pg. 343. On
day 1, there are seven
spots all lying on the same 'line of longitude' but on day 5, the points
nearest
the equator have rotated quicker and are pulling out ahead of the points
nearer
the poles.
Q: I completely do not understand the magnetic field of the
Sun and how it goes from north to south in the northern hemisphere
and from
south to north in the southern hemisphere in 11 year cycles.
A: Unfortunately no one completely understands this phenomenon.
We can
observe that it happens, then postulate some ideas as to why, but none
are
rock-solid explanations. It definitely seems to have to do with
the fact that the sun
rotates faster at the equator than closer to the poles. This
seems to wind
up the magnetic fields, causing kinks. Then about every eleven
years (give
or take a few years) the magnetic field becomes so kinked and wound
up, it goes
"boing!" and straightens itself out by flipping polarity. The
details are sketchy.
Q: the section called "Changes in the Solar System" had me
confused. When it says it is not always 11 years but actually
22 years and
can be as small as 7 years, what does this mean? Does that mean
it is not
constant? Or with time it changes? Please expound upon
this property.
A: It takes an average of 11 years for the sun to go from a period of
sunspot maximum (the time when the magnetic field is the most kinked)
through a
period of sunspot minimum, then back to a period of maximum.
During that 11 year
period, the sun has flipped the polarity of its magnetic field.
It takes another 11
years for the field to get flipped back to its original polarity, hence
the
statement that the solar cycle is 22 years when you take polarity into
account.
Now although the average time between periods of sunspot maxima is 11
years,
sometimes it only takes 7 years, and sometimes it takes as long as
16 years.