Imagine a celestial engine so vast that its diameter could swallow a million Earths, yet so precisely balanced that its nearly perfect sphere holds 99.86% of our solar system's mass in a seething, dynamic fusion core.
Key Takeaways
- The Sun's equatorial diameter is precisely 1,392,684 kilometers
- The Sun's equatorial radius measures 695,700 kilometers
- The Sun's polar diameter is 1,392,060 kilometers due to slight oblateness
- The Sun's core pressure is 265 billion bar
- The Sun's core radius is 20-25% of solar radius or about 170,000 km
- The Sun's radiative zone extends from 0.25 to 0.7 solar radii
- The Sun's photosphere thickness is approximately 100-500 kilometers
- Photospheric temperature decreases outward from 6,400 K to 3,500 K
- Sun's photosphere granulation has brightness contrast of 15-20%
- Sun's corona extends millions of km, visible during eclipses
- Coronal temperature averages 1-3 million Kelvin
- Sun's coronal mass ejections (CMEs) expel 10^9 to 10^12 tons of plasma
- The Sun's 11-year Schwabe cycle has sunspot number peaking every 11 years
- Maunder minimum from 1645-1715 had few sunspots
- Sunspot cycle 25 began December 2019, peak expected 2025
The Sun is an immense, dynamic, and mostly spherical star powered by nuclear fusion.
Atmosphere
- The Sun's photosphere thickness is approximately 100-500 kilometers
- Photospheric temperature decreases outward from 6,400 K to 3,500 K
- Sun's photosphere granulation has brightness contrast of 15-20%
- Average granule lifetime in photosphere is 8-20 minutes
- Sunspot umbra temperature is 4,100-4,700 K, cooler than surroundings
- Photospheric faculae are bright regions 10% hotter than average
- Sun's limb darkening coefficient follows Eddington-Barbier relation
- Optical depth tau=2/3 defines visible photosphere surface
- Supergranules in photosphere span 30,000 km with 5-hour lifetime
- Mesogranules average 5,000-10,000 km diameter
- Sun's photospheric magnetic field averages 1 gauss, up to 3,000 G in spots
- Wilson depression in sunspots is 200-1,000 meters deep
- Photospheric velocity oscillations have 5-minute period p-modes
- Sun's chromosphere extends 2,000-3,000 km above photosphere
- Chromospheric spicules reach heights of 10,000 km at 20-30 km/s
- Temperature minimum at 500 km above photosphere is 3,800-4,200 K
- Chromospheric network shows magnetic concentrations at supergranule boundaries
- Fibrils in chromosphere are dark absorption features 300 km wide
- Sun's H-alpha plages are bright chromospheric regions around sunspots
- Chromospheric temperature rises to 20,000 K at upper boundary
- Prominences in chromosphere/mantle mass 10^10 to 10^12 kg
- Sun's mottles are short-lived spicule-like features 5,000-10,000 km long
- Dynamical chromosphere shows 3-7 minute oscillations
- Sun's transition region between chromosphere and corona is 100 km thick
- Chromospheric Ca II K-line bright points indicate magnetic activity
Atmosphere Interpretation
Even though its radiant photosphere appears serene from afar, our Sun is actually a broiling, magnetically complex star whose skin crackles with granules like popping corn, whose blemishes are planet-sized storms of comparative chill, and whose upper atmosphere bristles with million-degree jets and vast, glowing loops anchored in a relentless, simmering turmoil.
Corona and Solar Wind
- Sun's corona extends millions of km, visible during eclipses
- Coronal temperature averages 1-3 million Kelvin
- Sun's coronal mass ejections (CMEs) expel 10^9 to 10^12 tons of plasma
- Solar wind speed at 1 AU is 300-800 km/s fast/slow streams
- Corona's density at base is 10^-12 g/cm³, drops to 10^-24 at 1 AU
- Sun's Alfvén critical surface at 10-20 solar radii for solar wind acceleration
- Coronal holes are source of fast solar wind at 700-800 km/s
- Sun's streamer belt divides hemispheres in corona during solar minimum
- Solar wind mass loss rate is 2-3 × 10^-14 solar masses per year
- Corona's X-ray brightness varies with 11-year cycle
- Sun's helmet streamers form pseudostreamers in corona
- Coronal loops have lengths 10,000-500,000 km with 10^6 K temperatures
- Solar wind dynamic pressure at 1 AU is 2-3 nPa
- Sun's coronal dimming regions follow CMEs with density drops 20-50%
- Heliospheric current sheet warps into ballerina skirt shape
- Sun's sigma parameter for CME magnetic flux is up to 10^22 Mx
- Coronal rain consists of 10^4-10^5 K plasma falling at 50-200 km/s
- Solar wind proton flux at 1 AU is 5 cm^-3
- Sun's quasi-streaming electrons in corona reach 0.1c speeds
- Coronal heating via nanoflares totals 10^27 erg/s over active regions
Corona and Solar Wind Interpretation
The Sun wears its corona like a dazzling but volatile crown, a million-degree halo that breathes billion-ton storms and whispers a supersonic wind across the solar system, all while keeping its own explosive secrets on a tight, eleven-year leash.
Interior Structure
- The Sun's core pressure is 265 billion bar
- The Sun's core radius is 20-25% of solar radius or about 170,000 km
- The Sun's radiative zone extends from 0.25 to 0.7 solar radii
- The Sun's convective zone thickness is from 0.7 to 1.0 solar radius
- The Sun's tachocline layer is 0.05 solar radii thick at base of convection zone
- Fusion in Sun's core fuses 620 million metric tons of hydrogen per second
- The Sun's core produces 99.9% of its energy via proton-proton chain
- Sun's core density peaks at 150 g/cm³
- Energy generation rate in core is 276 watts per cubic meter average
- Neutrinos from core number 6.5 × 10^10 per cm² per second at Earth
- Sun's pp neutrino flux is 6.1 × 10^10 /cm²/s
- CNO cycle contributes 1.7% of core fusion energy
- Sun's luminosity from core travels 171,000 to 1 million years to surface
- Radiative zone opacity dominated by H- ion absorption
- Convection zone carries 1% of Sun's energy outward
- Sun's differential rotation originates in tachocline shear
- Helium abundance in core is 34% by mass
- Sun's central temperature gradient follows Kelvin–Helmholtz mechanism initially
- Energy flux in radiative zone is 6.3 × 10^6 erg/cm²/s
- Sun's overshoot region extends 0.01-0.05 solar radii into radiative zone
- Convection cells (granules) average 1,000 km diameter in photosphere
- Sun's internal sound speed peaks at 500 km/s in core
- Helioseismology reveals p-mode frequencies up to 5 mHz
- Sun's core rotation rate is 430 nHz, uniform
- Fractional helium mass Y=0.25 in convection zone
- Sun's energy output per proton fused is 26.73 MeV
- ppI chain branch produces 69% of neutrinos
- Sun's core composition: 70% H, 28% He, 2% metals by mass
Interior Structure Interpretation
While outwardly just a gently warming orb, the Sun internally operates as a relentless, multimillion-degree factory where 620 million tons of hydrogen are annihilated every second in a crush of unimaginable pressure, a process so inefficient per cubic meter that it requires a core the size of twenty Earths and a leisurely hundred-thousand-year journey just to get a single photon to the surface.
Physical Properties
- The Sun's equatorial diameter is precisely 1,392,684 kilometers
- The Sun's equatorial radius measures 695,700 kilometers
- The Sun's polar diameter is 1,392,060 kilometers due to slight oblateness
- The Sun's mass is 1.9885 × 10^30 kilograms, accounting for 99.86% of the Solar System's total mass
- The Sun's mean density is 1.408 grams per cubic centimeter
- The Sun's surface gravity is 274 meters per second squared, 28 times Earth's
- The Sun's escape velocity from the surface is 617.7 kilometers per second
- The Sun rotates once every 25.05 days at the equator
- The Sun's rotation period at 30° latitude is 28 days
- At solar poles, the Sun rotates every 34.4 days
- The Sun's oblateness is 9 × 10^-6, nearly spherical
- The Sun's luminosity is 3.828 × 10^26 watts
- The Sun's bolometric magnitude is 4.83
- The Sun's absolute visual magnitude is 4.83
- The Sun's mean surface temperature is 5,772 Kelvin
- The Sun's core temperature reaches 15.7 million Kelvin
- The Sun's photospheric temperature averages 5,778 K
- The Sun's volume is 1.412 × 10^18 cubic kilometers
- The Sun is 109.3 times Earth's diameter
- The Sun's mass is 333,000 times Earth's mass
- The Sun's density is 1/4th of Earth's density at 1.41 g/cm³
- The Sun's angular diameter from Earth is 31.6 to 32.7 arcminutes
- The Sun's distance from Earth averages 149.6 million kilometers or 1 AU
- The Sun's heliocentric longitude of ascending node is 0°
- The Sun's age is approximately 4.6 billion years
- The Sun's expected lifespan is 10 billion years total
- The Sun's current main sequence phase is halfway through at 5 billion years remaining
- The Sun's spectral classification is G2V
- The Sun's metallicity [Fe/H] is 0.00 dex
- The Sun's surface rotation velocity at equator is 7.284 km/s
Physical Properties Interpretation
Despite being a nearly perfect sphere of serene plasma, the Sun is a tyrannical, middle-aged furnace that rotates like a lazy top, contains almost every scrap of matter for light-years, and will, in its own sweet cosmic time, cook us all.
Solar Activity
- The Sun's 11-year Schwabe cycle has sunspot number peaking every 11 years
- Maunder minimum from 1645-1715 had few sunspots
- Sunspot cycle 25 began December 2019, peak expected 2025
- Average sunspot number maximum is 120-150 during cycle peaks
- Solar flares classified A<B<C<M>X by peak flux in 1-8 Ångstroms
- Largest recorded flare was X45 in 2003 from GOES satellite
- Sun's active regions have magnetic fields 100-3,000 gauss
- Filament eruptions produce 50% of CMEs
- Solar cycle length varies 9-14 years, average 11 years
- Sunspot butterfly diagram shows migration from 30° to equator
- Hale's polarity law: leading spots opposite polarity in hemispheres, reverses per cycle
- Joy's law: sunspot tilt increases with latitude, 2.5-5° per degree
- Solar maximum of cycle 24 had smoothed sunspot number 116 in 2014
- Flares release 10^24 to 10^29 ergs energy
- Sun's 27-day rotation periodicity seen in geomagnetic storms
- Gnevyshev split: secondary maximum in odd cycles at 1.5 years after primary
- Solar dynamo Babcock-Leighton model explains cycle via flux transport
- Active longitudes persist 140-360 days with enhanced activity
- Sunspot groups classified by Zurich system: A, B, C, D, E, F, G, H types
- Magnetic helicity buildup leads to flares via reconnection
- Solar cycle 25 prediction: peak sunspot number 115 in July 2025
- Dalton minimum 1790-1830 had reduced activity
- Spörer minimum 1460-1550 coincided with Little Ice Age onset
Solar Activity Interpretation
Despite its reputation for being a steady cosmic metronome, our Sun is a fickle, magnetically-driven drama queen whose 11-year sunspot tantrums, occasional centuries-long sulks, and explosive X-class outbursts have been meticulously catalogued by patient astronomers, all to predict its next fiery mood swing with only moderate confidence.