How the Sun Shines: The Nuclear Reactions that Power the Sun

The Sun was always a bit of a mystery.

No one could figure out what was powering it.

In the 19th century, some scientists thought it could all be explained by gravity.

The Sun began as a giant cloud of dust and gas.

And this cloud collapsed under the force of gravity releasing lots of heat.

This might explain why the Sun is hot, but it doesn't explain why the Sun has been hot for so long.

A clear picture didn't emerge until we had a better model of the atom.

At the center of each atom is a tiny nucleus made of protons and neutrons.

Protons have a positive electric charge and this is a problem because their charges are pushing them apart.

The electric force is trying to rip apart the nucleus.

But there is a strong force holding it together: the nuclear force.

The nuclear force brings protons and neutrons together.

It doesn't really affect pairs of protons or pairs of neutrons.

To hold everything together you need to have just the right combination of protons and neutrons.

Too many protons and it falls apart.

Too many neutrons and it falls apart.

But when you get just the right combination, you produce a nuclear reaction.

Nuclear reactions are similar to chemical reactions in many ways.

There are certain combinations of chemicals that are more stable. When you form stable compounds, you make energy.

For example, if you combine hydrogen and oxygen to make H₂0, this is a more stable combination and you make energy.

Similarly, if you combine two hydrogen nuclei into Helium, this is a more stable combination and you make energy.

But nuclear reactions are different from chemical reactions.

They're much harder to produce, they're much more powerful, and they involve neutrons.

Chemical reactions are part of our everyday life, but nuclear reactions are not. The reason is that the nuclear force only works over very short distances.

The protons are all positively charged.

So if you bring hydrogen nuclei together, they just repel each other.

If you bring them closer, they repel each other more.

The nuclear force only kicks in when they are extremely close.

Normally, the nuclei never get near each other.

It is only under conditions of extreme pressure and extreme heat that the nuclei will collide.

And this only happens at the center of a very massive object like our Sun or inside a nuclear bomb.

Neutrons are very important in nuclear reactions, but for chemical reactions they're irrelevant.

This is a hydrogen nucleus and so is this.

For the purposes of chemistry, we don't care about the neutrons.

But for nuclear reactions, we do.

We have to keep track of them.

So this is a Hydrogen-1 nucleus.

And this is a Hydrogen-2 nucleus.

The number at the end is the total number of protons and neutrons.

Two protons and a neutron make Helium-3.

Two and two make Helium-4.

Hydrogen-2 is also known as Deuterium.

Nuclear reactions are very powerful.

Let's look at our two reactions again.

The chemical reaction releases 5 eV of energy.

The nuclear reaction releases 24 million eV of energy.

So the nuclear reaction is 5 million times more powerful.

There's enough energy in just a pound of deuterium to power 10,000 homes for a year.

This is an insane amount of energy.

It's why the Sun is so bright, why nuclear bombs are so scary, and why scientists have been working on fusion power for decades with little success.

There's another nuclear force that we need to talk about.

We've been talking about the strong nuclear force, but there's also a weak nuclear force.

The strong force is what holds the nucleus together.

The weak force causes radioactivity.

And it's called the weak force because it acts slowly.

The weak force can cause protons and neutrons to switch identities.

A proton can turn into a neutron.

Or a neutron can turn into a proton.

This is called beta decay.

Neutrons are heavier than protons just barely.

But what this means is that a free neutron can lose some mass and turn into a proton.

But a proton cannot turn into a neutron unless it's near other particles.

The reason this process is called beta decay is because it's one of the ways that a radioactive element can decay.

Now it turns out that radioactivity can be slow.

Imagine you have a box full of Uranium-235 atoms.

Eventually, the Uranium atoms will all turn into Lead, but they're not in any hurry to do this.

If you want to wait until half your Uranium atoms have turned into Lead, you'll be waiting 700 million years.

Radioactivity involves more than just beta decay.

There's actually more going on here.

But the point is that beta decay can be a slow process and it's a random process.

Now we finally have covered enough background to explain how the Sun shines.

This was worked out in the 30s by Hans Bethe.

The Sun is mostly made of Hydrogen-1 which is just a proton.

The Sun is very hot and very dense so these protons collide.

But this doesn't cause a nuclear reaction because there are no neutrons.

Most of the time when two protons collide they immediately fly apart producing no energy.

But it is possible, very very rarely, that something else happens: beta decay.

At the moment the two protons collide, one of them undergoes beta decay and turns into a neutron.

This gives us Hydrogen-2 and releases tons of energy.

The Hydrogen-2 nucleus continues moving around and when it bumps into a proton it turns into Helium-3 and this releases tons of energy.

As this process continues, the Sun produces more and more Helium-3.

When two Helium-3 nuclei collide, they can form an even better combination,  Helium-4 and this releases tons of energy.

Hydrogen is converted into Helium in three steps.

First, two protons are combined into Deuterium through beta decay.

Next, a proton is added to make Helium-3 and finally, two Helium-3 nuclei collide creating

Helium-4 plus two leftover protons.

The first step is by far the slowest because you have to wait for beta decay.

For a typical proton in the center of the Sun, the first step takes on average one billion years.

Compare that to the second step which takes about 4 seconds.

Now in the final step, you have to find another Helium nucleus which is rare.

This takes about 400 years. These nuclear reactions are the source of the Sun's tremendous power.

The Sun is the ultimate energy source.

The Sun heats the air which causes wind.

The Sun heats water which causes rain giving us hydroelectric power.

Sunlight is the foundation of life.

The energy from ancient sunlight was deposited into the ground giving us our fossil fuels:

coal, oil, and natural gas.

Practically all the world's energy ultimately comes from either the Sun or nuclear power.

To summarize, we present Children Explaining Nuclear Physics.

Hydrogen-1 atoms.

The Sun is made up of most of these.

Now what if two of them collide?

Then one of them will turn into a neutron and you get Hydrogen-2.

Next, it collides with another atom and becomes Helium-3.

And then it collides with another one and you get Helium-4.

Beautiful!

Quiz: What Are Asteroids And Where Do They Come From?

Preview Test: What Are Asteroids And Where Do They Come From?

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QUESTION 1
Asteroids are known to be composed of clay and rocks, as well as metals like nickel and _______.

Hint

10 points

QUESTION 2
An asteroid is a small, rocky object that orbits the sun, just like the rest of the planets and celestial bodies in our solar system.

Although asteroids are present throughout the solar system, most of them live in the ............... — a region located between the orbits of Mars and Jupiter.

Hint

asteroid hoop
asteroid belt
asteroid way
asteroid city
asteroid orbit
asteroid ring
asteroid country
asteroid location
asteroid circle

10 points

QUESTION 3
Asteroids are found in three main regions of our solar system.

A significant amount of asteroids are found in the Asteroid ____, which lies between _____ and Jupiter.
Then there are _____ asteroids—a large group of asteroids that share the orbit of planets around the Sun.
Jupiter Trojans are the most well-known and numerous Trojans.
The total number of Jupiter trojans larger than 1 km in diameter is believed to be about 1 _______!

Finally, there are Near Earth Asteroids, or _____.
These circle closer to Earth than the sun.
It is believed that nearly 10,000 of all known asteroids are NEAs.

Hint

10 points

QUESTION 4
An asteroid capable of causing a global apocalypse would have to be more than 400 ______wide.
Impact from such an asteroid would cause massive destruction of both life and property on a global scale.
Fortunately, asteroids that huge strike Earth an average of once every 1000 _______.
All in all, asteroids can and do orbit near our planet, but most will never approach Earth, and even if they do, they usually get burned up in the atmosphere before ever making contact with our planetary surface.

Hint

10 points

QUESTION 5
Asteroids orbit the sun in _____ orbits, but additionally, they also ______, sometimes tumbling haphazardly through space.

Hint

10 points

QUESTION 6
The size of objects within the asteroid belt have a wide range, from being no bigger than a dust particle to almost a ........... wide.

Hint

ten thousand centimeters
ten thousand meters
thousand kilometers
hundred kilometers
hundred centymeters
thousand centimeters
hundred meters
ten thousand kilometers
ten kilometers
thousand meters

10 points

QUESTION 7
According to NASA, space rocks smaller than 25 meters will most likely burn up as they enter Earth's atmosphere.
However, some larger asteroids do make it through the atmosphere and impact our planet’s surface.
In 2013, an asteroid slammed into the atmosphere over the Russian city of .........
The shock wave created by this event injured 1,200 people.

Hint

Chihuahua
Chelmsford
Chengzhou
Moscow
Changzhou
Chicago
New York
Cheboksary
Chelyabinsk
London

10 points

QUESTION 8
Asteroids are also cratered or pitted, and their surface is thought to be covered in _________.

Hint

10 points

QUESTION 9
The largest asteroid from the asteroid belt, which is considered a dwarf planet.
__________
Hint

10 points
QUESTION 10

Our solar system came into existence about .............. years ago when a large cloud of gas and dust collapsed.

Hint

46 billion
460 billion
4.6 million
4.6 billion
46 thousand
460 million
46 million
4,600 billion
460 thousand

10 points


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What Are Asteroids And Where Do They Come From?

One of the most well-known theories concerning the death of the dinosaurs argues that these ancient creatures went extinct when a large stone from space slammed into Earth.
Through a series of events, this ultimately led to the extinction of dinosaurs.
You have probably heard countless stories and hypotheses regarding the disastrous consequences of an asteroid strike on Earth, but what exactly are asteroids?
Where do they come from?
And most importantly, could they really obliterate the entire planet if they were to strike Earth with enough force?
An asteroid is a small, rocky object that orbits the sun, just like the rest of the planets and celestial bodies in our solar system.
Although asteroids are present throughout the solar system, most of them live in the asteroid belt—a region located between the orbits of Mars and Jupiter.
The size of objects within the asteroid belt have a wide range, from being no bigger than a dust particle to almost a thousand kilometers wide.
In fact, the largest asteroid present in the asteroid belt—Ceres—is 940 kilometers wide and is considered a dwarf planet.
Although the asteroid belt hosts a multitude of asteroids, it’s not the only region where these rocky objects hang around.
Some asteroids are also found in the orbits of planets, which means that the planet and the asteroid circle the sun on the same elliptical path.
Earth and a few other planets have asteroids like this.
For some, a more interesting question is, how did these asteroids come into being?
Our solar system came into existence about 4.6 billion years ago when a large cloud of gas and dust collapsed.
Following this event, most of that material fell to the center of the cloud and resulted in the formation of the sun—the central star of our solar system.
Planets were formed from some of the condensing dust in that cloud, but not all celestial material had the chance to be incorporated into planets.
The leftovers from that time took the form of asteroids.
Asteroids vary greatly in terms of their shape and size.
An asteroid can be as large as Ceres, nearly a thousand kilometers wide.
On the other end of the spectrum, the smallest asteroid ever studied is a space rock called 2015 TC25.
It’s 2 meters wide and was observed when it made a close flyby of Earth in October 2015.
Almost all asteroids are irregularly shaped, although a few big ones, like Ceres, are nearly spherical.
Asteroids are also cratered or pitted, and their surface is thought to be covered in dust.
Asteroids orbit the sun in elliptical orbits, but additionally, they also rotate, sometimes tumbling haphazardly through space.
They may even have their own moons! We know of more than 150 asteroids that have a small companion moon, and some have more than one! Asteroids are found in three main regions of our solar system.
A significant amount of asteroids are found in the Asteroid belt, which lies between Mars and Jupiter.
Then there are Trojan asteroids—a large group of asteroids that share the orbit of planets around the Sun.
Jupiter Trojans are the most well-known and numerous Trojans.
The total number of Jupiter trojans larger than 1 km in diameter is believed to be about 1 million! Finally, there are Near Earth Asteroids, or NEAs.
These circle closer to Earth than the sun.
It is believed that nearly 10,000 of all known asteroids are NEAs.
Asteroids are known to be composed of clay and rocks, as well as metals like nickel and iron.
Now, since some asteroids are very close to Earth, in comparison to other celestial bodies, Is it possible for them to slam into our planet?
Absolutely! Ever since Earth came into being, it has been struck relentlessly by asteroids and comets.
In fact, the most popular theory regarding the extinction of dinosaurs is related to an asteroid that slammed into Earth, causing widespread destruction, obliterating most life forms in the global aftermath.
Although many celestial objects approach our planet, a significant number of them get burned up in the atmosphere and never make it to Earth’s surface.
According to NASA, space rocks smaller than 25 meters will most likely burn up as they enter Earth's atmosphere.
However, some larger asteroids do make it through the atmosphere and impact our planet’s surface.
In 2013, an asteroid slammed into the atmosphere over the Russian city of Chelyabinsk.
The shock wave created by this event injured 1,200 people.
An asteroid capable of causing a global apocalypse would have to be more than 400 meters wide.
Impact from such an asteroid would cause massive destruction of both life and property on a global scale.
Fortunately, asteroids that huge strike Earth an average of once every 1000 centuries.
All in all, asteroids can and do orbit near our planet, but most will never approach Earth, and even if they do, they usually get burned up in the atmosphere before ever making contact with our planetary surface.

Student Mistakes

 

A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. 
The primary greenhouse gases in Earth's atmosphere are water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O₃).
Without greenhouse gases, the average temperature of Earth's surface would be about −18 °C (0 °F), rather than the present average of 15 °C (59 °F). 
The atmospheres of Venus, Mars and Titan also contain greenhouse gases.

Answer: 1.12E2 

Do not enter ±1%.
One percent here is the range of answers that the test system evaluates as correct. Deviation of the student's answer from the correct value by less than one percent is not considered an error.

Here's the general rule for rounding:

If the number you are rounding is followed by 5, 6, 7, 8, or 9, round the number up. 

Example: 1.235 rounded to the 3 significant figures is 1.24

If the number you are rounding is followed by 0, 1, 2, 3, or 4, round the number down. 

Example: 1.234 rounded to the 3 significant figures is 1.23 

From the hint, use radii: the radius of the Earth is 1 radius of the Earth. The radius of Jupiter is equal to 11.19 radii of the Earth. Calculate the ratio: 11.19 / 1 = 11.19

Don't convert the result from regular notation to scientific notation, as this question doesn't have that requirement. 

If the diameter of the first spherical object is 3 times the diameter of the second spherical object, then how many times the volume of the first object is greater than the second. Hint

Given Answer:  3 Correct Answer:  27

Solution
From the hint: 

Then:
V₁/V₂ = (πd₁³/6) / (πd₂³/6) = d₁³/d₂³ = (d₁/d₂)³ = 3³ = 3⨯3⨯3 = 27

The orbital period of a satellite is the time it takes for it to complete one revolution around the Earth. Since the satellite is geostationary, this means that this time must be equal to the time of one rotation of the Earth around the Earth's axis of rotation, but it must be observed relative to the stars. So, the answer is a sidereal day. But we know (see the hint) that a sidereal day is about 4 minutes shorter than a solar day. So the answer is: 24 hours - 4 minutes = 23 hours 56 minutes.

Method of the calculation

In your internet browser make the copy of the text of the formula.

Then paste the text to the Google search of your internet browser.

Replace the degrees angle symbols with the word "degrees":

sin -106degrees  +   cos 296degrees   /   (sin -326degrees  - tan 236degrees ) 

Click "enter". 

The Google will give you following result: 

-1.43601403294

Transform this number from normal notation to the scientific notation for computers with 3 significant figures: 

-1.44E0

Asteroids, Comets, and Dwarf Planets: Their Nature, Orbits, and Impacts

 21) What characteristic distinguishes a meteorite from a terrestrial rock? 

A) A meteorite is usually covered with a dark crust from burning in Earth's atmosphere. 

B) A meteorite usually has a high metal content. 

C) Meteorites have different isotope ratios of particular elements when compared to terrestrial rocks. 

D) Meteorites contain rare elements, such as iridium, that terrestrial rocks do not. 

E) All of the above are true. 

Answer:  E

22) Primitive meteorites can be distinguished from other meteorites and terrestrial rocks because they 

A) contain a noticeable fraction of pure metallic flakes. 

B) resemble the composition of Earth's core. 

C) contain a lot of iron and were used by humans to make iron tools. 

D) resemble the composition of Earth's mantle. 

E) resemble the composition of rocks from lava flows that occurred on asteroids very shortly after the formation of the solar system. 

Answer:  A

23) Most meteorites are 

A) carbon-rich and primitive. 

B) rocky and primitive. 

C) carbon-rich and processed. 

D) rocky and processed. 

E) iron-rich and processed. 

Answer:  B

24) Processed meteorites with low metal content probably are 

A) leftover chunks of rock from the earliest period in the formation of the solar system. 

B) pieces of comets rather than of asteroids. 

C) chunks of a larger asteroid that was shattered by a collision. 

D) chunks of rock chipped off the planet Mercury. 

E) chunks of rock chipped off the planet Mars. 

Answer:  C

25) Meteorites can come from 

A) the cores of asteroids. 

B) the Moon. 

C) Mars. 

D) comets. 

E) all of the above 

Answer:  E