Everything you need to know about the Sun
An interactive study guide built from your three note decks: the Sun's life and characteristics, its layered structure, and the 11-year solar cycle that drives space weather. Read, flip, quiz yourself — then check it off.
A whole unit in three note decks
This guide turns Mrs. Dickinson's Sun notes into one continuous study flow. Work top to bottom, or jump straight to whatever you need to review.
1 · Read the three units
Characteristics, structure, and the solar cycle. Each unit ends with the same check-for-understanding questions from your notes.
2 · Drill the flashcards
Thirty-two cards across all three units. Flip, shuffle, and keep going until the answers feel automatic.
3 · Prove it with the quiz
Sixteen questions with instant explanations. Your best score and studied sections are saved in this browser.
Identify the approximate mass, size, motion, temperature, structure, and composition of the Sun.
Distinguish between nuclear fusion and fission, and identify the Sun's source of energy.
Describe the 11-year solar cycle and the significance of sunspots.
Analyze the origins and effects of space weather — solar wind, CMEs, prominences, flares, and sunspots.
Demonstrate the use of astronomical units and light years, minutes, and seconds.
Characteristics of the Sun
Life, death, and the numbers: how the Sun formed, what powers it, how it will end, and the vital statistics that describe it.
Vital statistics
The approximate size, mass, distance, temperature, and composition of the Sun.
1,390,000 km
109× wider than Earth
2 × 10³⁰ kg
333,000× Earth's mass
99.8%
Its gravity rules the system
30× Earth
You'd feel very heavy there
1 AU
149,600,000 km / 92 million mi
~8 light minutes
Sunlight you see left the Sun 8 minutes ago
~4.5 billion years
Born from a stellar nebula
H 71% · He 27%
Measured from surface spectra
How the Sun works
Nuclear fusion is the source of the Sun's energy — not fission. Gravity and pressure must stay balanced.
What the Sun does
The joining of 2 or more lighter atoms into a larger atom. The Sun fuses hydrogen into helium: H + H = He. Matter turns into energy!
- Fusion powers the Sun — its source of nuclear energy.
- Takes place in the core, then energy works its way outward.
- Powers every main sequence star.
NOT what the Sun does
The splitting of larger atoms into 2 or more smaller atoms. Do not confuse it with fusion!
- Used in nuclear power plants and some weapons on Earth.
- The Sun does not split atoms for energy.
- If it did, the Sun would behave completely differently.
The Sun balances gravitational forces (inward) against pressure from atomic collisions (outward).
Without that equilibrium, the Sun would collapse.
Life and death of the Sun
All stars start the same way. Mass decides how long they stay on the main sequence — and how they end.
- 1
Stellar Nebula
4.5 billion years agoDeep inside a stellar nebula, gravity pulled dust and gas together.
- The cloud coalesced (came together), spun, and flattened into an accretion disk.
- The accretion disk became the planets.
- 2
Protostar
Before fusion beginsMaterial clumped together in the center forming a "baby star."
- Gravity keeps compressing the clump of gas and dust.
- Once it starts fusing hydrogen, the protostar graduates to the next stage.
- 3
Main Sequence
NOW — the Sun's current stage We are hereOnce a star fuses hydrogen into helium, it becomes a main sequence star.
- The Sun is a yellow dwarf main sequence star.
- All stars begin life with stages 1, 2, and 3.
- Stars spend the majority of their lives in the main sequence.
- Mass determines how long a star stays in the main sequence — and what happens next.
- 4
Red Giant
In ~5.4 billion yearsThe Sun runs out of hydrogen; helium becomes unstable and fuses into carbon.
- As more hydrogen fuses into helium, the core shrinks, letting outer layers move closer to the core.
- That increases the Sun's gravitational force, fusion speeds up, and energy output rises — the Sun becomes hotter and brighter.
- The core compresses and the Sun expands, engulfing most of the inner solar system.
- 5
Planetary Nebula
After the red giant phaseGravity takes over, the Sun sheds its outer layers, and a planetary nebula forms.
- The Sun can no longer hold itself together.
- The shed layers change the outer solar system as well.
- 6
White Dwarf
Late in lifeThe Sun shrinks down to its core — a white dwarf — and continues fusing heavier and heavier elements until it burns completely out.
- Because of the Sun's smaller mass, it will NOT explode as a supernova.
- Earth would not survive to see this quiet ending as we know it.
- 7
Black Dwarf
The very endWhen the Sun's energy is gone and it has burnt out, it no longer shines — a black dwarf.
- A black dwarf is the cooled, dark remnant of a white dwarf.
- The universe may not even be old enough for one to exist yet!
Temperature ladder
From the core out to the corona — the upper atmosphere is unexpectedly hotter than the surface.
Where fusion happens — the hottest part.
The visible surface we see.
The upper atmosphere — hundreds of times hotter than the surface.
Bars use a logarithmic scale — otherwise the core would flatten everything else.
Location & motion
The Sun is one star in the Milky Way — and it isn't sitting still.
Galactic address
An arm of the Milky Way.
Orion Spur
Orbits
The black hole at the center of the Milky Way.
Sagittarius A*
Galactic year
One full trip around the galaxy.
~230 million years
Rotation at equator
Differential rotation — different speeds at different latitudes.
25.4 days
Rotation at poles
Differences likely due to temperature differences.
36 days
Check for understanding
7 questions · click to reveal
Structure of the Sun
Six layers, color-coded from the core out to the corona. Click a layer in the diagram — or in the list — to study it.
Click a ring to select that layer — 1 is innermost (core), 6 is outermost (corona).
Good to know
Details from the notes that tie the structure together.
Granulation
A manifestation of convection at the photosphere — hot, bright bubbles rising and cooler, darker material sinking, in cells roughly 20,000 km across.
Color-coding strategy
The notes use a rainbow mnemonic, inside → out: red core, orange radiative zone, yellow convective zone, green photosphere, blue chromosphere, purple corona.
Eclipse gave the clues
Total eclipses reveal the corona during totality, and annular eclipses reveal the reddish chromosphere — layers we otherwise can't see from Earth.
Check for understanding
4 questions · click to reveal
The 11-Year Solar Cycle & Space Weather
The Sun's magnetic field flips every 11 years. As it does, activity swings from solar minimum to solar maximum — and Earth feels the consequences.
Every 11 years, the Sun's magnetic field reverses. Differential rotation at the equator and poles tangles the magnetic field lines, and the north and south poles switch places. This can cause areas of the Sun to become very active and release energy.
Solar Minimum
Beginning of the cycle
- Fewer sunspots, and they appear at midlatitudes.
- Fewer flares and generally less activity.
Solar Maximum
Middle of the cycle
- More sunspots, appearing nearer the equator.
- More flares and generally more activity.
11 years
one full magnetic flip — north and south poles trading places — from minimum to minimum
Explore the 11-year cycle
Year 5.5 · Solar Maximum8 sunspots visible
The Solar Maximum officially started in December 2024.
Space weather, feature by feature
Six solar phenomena — what they are, and what they can do.
Sunspots
The dark marks on the photosphere
- Areas that are darker on the photosphere.
- Cooler than the areas around them, due to the strong magnetic fields there.
- Hundreds to thousands of kilometers across.
- Can last from a single day to months.
Solar Flares
Sudden explosions of energy
- Caused by the tangling, crossing, breaking, or reorganizing of the Sun's magnetic field.
- Cause an increase in radio and X-ray emissions.
- Originate near sunspots.
- Can last minutes or hours.
Prominences
a.k.a. Filaments · Huge loops of particles
- Anchored to the photosphere and extend into the corona.
- Can last several months.
- Loop out thousands of miles.
- Called filaments when seen against the disk.
Coronal Mass Ejections
Huge bubbles of radiation and particles
- Can accompany a solar flare.
- Released from the Sun and can shoot through the solar system.
- Can interfere with power grids, causing electricity shortages and power outages.
- Cause geomagnetic storms on Earth.
Solar Wind
A constant breeze of particles
- Generated because the corona's high temperatures give hydrogen and helium atoms enough energy to exceed escape velocity.
- These particles sweep through the solar system.
- Solar winds protect us from stray cosmic rays coming from other places in the galaxy.
Auroras
Lights near the poles
- Intense lights in the sky that form near the poles.
- Occur when charged particles from CMEs reach areas near the Earth.
- If the solar winds are strong enough, they push auroras further toward the equator.
- 1We can make preparations for possible disruptions to satellites and radio communications.
- 2We can make preparations for possible disruptions to electrical grids.
- 3We can prepare astronauts for when it is safe to leave their craft — and when it is best to stay in.
Check for understanding
5 questions · click to reveal
Flashcards
Thirty-two cards straight from the notes. Tap a card (or press space) to flip it, then arrow through the deck.
Keyboard shortcuts
- Flip card space
- Next card →
- Previous card ←
- Toggle dark mode d
Deck breakdown
- Characteristics17 cards
- Structure7 cards
- Solar Cycle8 cards
Study tip
Say the answer out loud before flipping. If you can explain the card to someone else — like why the corona is hotter than the surface — you own it.
Practice quiz
One question at a time, with instant feedback and an explanation for every answer. Your best score is saved automatically.
Reference sheet
The whole unit on one screen — handy the night before a test, or whenever a number slips your mind.
Numbers to know
- Diameter
- 1,390,000 km · 109× Earth
- Mass
- 2 × 10³⁰ kg · 333,000× Earth
- Share of solar system mass
- 99.8%
- Gravity
- 30× Earth
- Distance from Earth
- 149,600,000 km (92 M mi) = 1 AU
- Light travel time
- ≈ 8 light minutes
- Age
- ≈ 4.5 billion years → red giant in ≈ 5.4 billion
- Surface composition
- Hydrogen 71% · Helium 27%
- Core temperature
- 15,000,000 K (27,000,000 °F)
- Photosphere temperature
- 5,772 K (≈ 10,000 °F)
- Corona temperature
- 2,000,000 K (3,500,000 °F)
- Rotation
- Equator 25.4 days · poles 36 days
- Galactic orbit
- ≈ 230 million years around Sagittarius A*
Layers at a glance
- 1
Core · red
Nuclear fusion produces the Sun's energy.
- 2
Radiative Zone · orange
Energy moves slowly outward.
- 3
Convective Zone · yellow
Convection currents carry heat outward.
- 4
Photosphere · green
The literal, visible surface of the Sun.
- 5
Chromosphere · blue
Sculpted by the Sun's magnetic field.
- 6
Corona · purple
The solar (upper) atmosphere.
Units of measurement
Astronomical Unit (AU)
149,600,000 km
The average Earth–Sun distance (92 million miles). Sunlight takes ~8 light minutes to cover 1 AU.
Light second
299,792 km
The distance light travels in 1 second — nearly 300,000 km.
Light minute
~17,990,000 km
How far light travels in 1 minute — the Sun is about 8 of these away.
Light year
~9.46 trillion km
The distance light travels in 1 year — about 63,241 AU.
Space weather at a glance
| Feature | What it is | Effect on Earth |
|---|---|---|
| Sunspots | The dark marks on the photosphere | Areas that are darker on the photosphere. |
| Solar Flares | Sudden explosions of energy | Cause an increase in radio and X-ray emissions. |
| Prominences | Huge loops of particles | Anchored to the photosphere and extend into the corona. |
| Coronal Mass Ejections | Huge bubbles of radiation and particles | Can interfere with power grids, causing electricity shortages and power outages. |
| Solar Wind | A constant breeze of particles | Solar winds protect us from stray cosmic rays coming from other places in the galaxy. |
| Auroras | Lights near the poles | If the solar winds are strong enough, they push auroras further toward the equator. |
Glossary
The spinning, flattened disk of gas and dust left from a collapsing nebula, which became the planets.
Intense lights near the poles created when charged particles from CMEs reach near Earth.
The Sun's upper atmosphere, glowing in X-ray and UV, visible during a total solar eclipse.
The Sun spinning faster at the equator (25.4 days) than at the poles (36 days).
A manifestation of convection on the photosphere — cells of rising and sinking material about 20,000 km across.
A disturbance of Earth's magnetic field caused by space weather such as CMEs — it can knock out power grids.
The Sun's balance of gravity (inward) and pressure (outward); without it the Sun would collapse.
The "baby star" stage of a collapsing clump of gas and dust before fusion starts.
The black hole at the center of the Milky Way that the Sun orbits every ~230 million years.
Jets of hot gas in the chromosphere.
A cloud of dust and gas where all stars begin — the Sun's story started 4.5 billion years ago in one.