Earth has a star {Sun}.
location
Sun is in galaxy horizontal plane, 27,000 light-years, 2/3 galaxy radius, from galaxy center, in Sagittarius arm.
orbit
Orbit around galaxy takes 2.5 x 10^6 years.
speed
Speed through space is 12 miles/second. Speed around galaxy is 150 miles/second.
formation
Sun and solar system formed 4,600,000,000 years ago, from gas cloud.
energy
Sun electromagnetic radiation is 10^33 ergs per second. Photons from Sun hit Earth with energy 1 eV, which is average needed for chemical reactions.
properties
Sun gas has atomic nuclei and electrons, with density 1.5 g/cm^3 at surface. Sun has average size. Mass is 2 x 10^30 kilograms, 10^6 times Earth mass. Diameter is 432,000 miles.
temperature
Temperature is 10^7 K at center and 5800 K at surface.
rotation
Equator rotates once every 27 days, around axis perpendicular to ecliptic. Polar regions rotate once every 23 to 24 days.
vibration
Sun vibrates with period 10 to 48 minutes after surface activity.
cycle
Sunspots, solar flares, and magnetic storms follow cycle of 11.1 years, with maximum at 1994 and 2005.
Light intensity from edge is 70% less than from center {limb-darkening}. Center is hotter. Edge is cooler. Edge light has to travel longer through Sun atmosphere.
Bright spots can be at Sun sides {parhelion}.
Inner sphere {inner core, Sun} has most of Sun mass and rotates once a day.
In next layer {radiative zone}, heat transfers only by radiation, not convection.
In layer {convective zone} under surface, turbulence and shock waves transfer heat by convection and make sunspots. Convective zone has 1% of Sun mass and 20% of radius.
Convective-zone gas-circulation pattern has 1,000,000-m swirls {granulation} and 30,000,000-m swirls {supergranulation}.
Strong magnetic fields near surface cause lower darker regions {sunspot}| of cooler 3900-K gas. Sunspots last 1 to 21 days and are 1 to 10 times wider than Earth. Sunspots start as small specks in horizontal belt, coagulate to make east-west pair, and then drift toward equator. Small sunspots {pore, Sun} can be near sunspots.
Above convective zone is layer {photosphere} that makes visible light, at 5700 K.
The layer {chromosphere} above photosphere makes star color, at 4500 K to 35,000 K. Photosphere and chromosphere are 9000 miles thick.
Chromosphere has luminous-material columns {spicule, Sun} 500,000 meters wide and 1,000,000 meters high, lasting 10 minutes.
Above chromosphere, low-density yellow layer {inner corona} extends from 9000 miles above surface to 300,000 miles above surface and is 10^5 to 10^6 K. Temperature is due mostly to solar flares. Alfven magnetic waves, whose field can oscillate but at constant pressure or which can change pressure like sound waves, affect temperature slightly. Corona temperature and density decrease over poles {coronal hole}.
High-speed electron and atomic-nucleus streams {solar prominence} {solar flare}| arch from chromosphere into inner corona, up to 400,000,000 meters high and 50,000,000 meters wide, for up to 30 minutes. Solar flares can make x-rays. Sunspots and solar flares can have large plasma ejections {coronal mass ejection} (CME).
cause
Magnetic lines with opposite polarity squeeze together along current sheet, where they break to form new ends that connect {magnetic field reconnection} {Sweet-Parker magnetic reconnection} {slow reconnection} {Petschek magnetic reconnection} {fast reconnection} with opposite-polarity lines and annihilate.
Corona high temperature is due mostly to solar flares. Magnetohydrodynamic waves {Alfven wave}, whose field can oscillate but at constant pressure or which can change pressure like sound waves, affect temperature slightly.
Above inner corona, a low-density white gas layer {outer corona} {K corona} ends 10^6 miles from surface.
Outer corona expands away from Sun in waves {solar wind}|, as 5 x 10^5 tons of charged particles per second leave at 500,000 meters per second.
Cool gas and dust {F corona} surround outer corona.
Sun has a magnetosphere {heliosphere}. Ionized-gas convection makes magnetic fields. Because Sun plasma conducts, magnetic fields flow around convective zone and core. Faster rotation at equator wraps magnetic force lines around Sun, making stronger magnetic field than with no wrapping: 1000 gauss rather than 1 gauss like Earth. Magnetic-force lines repulse each other, making gas less dense there.
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Date Modified: 2022.0225