Spectral
Type: G2 V Luminosity: 3.83 x
10 33 ergs/sec.
Age: 4.6 Billion Years
Synodic Period: 27.2753 days
Rotation Period at Equator: 26.8
days
Rotation Period at Poles: 36 days
Velocity Relative to Near Stars:
19.7 km/s
Mean Distance to Earth: 149.60
million km (92.96 million mi) (1 astronomical unit)
Solar Constant (Total Solar
Irradiance): 1.365 - 1.369 kW/m2
(at the mean distance of the earth from the Sun, about one AU)
Sun/Earth
Comparison
Bulk parameters
Sun Earth Ratio (Sun/Earth)
Mass (1024 kg) 1,989,100. 5.9736 333,000.
GM (x 106 km3/s2) 132,712. 0.3986 333,000.
Volume (1012 km3) 1,412,000. 1.083 1,304,000.
Volumetric mean radius (km) 696,000. 6371. 109.2
Mean density (kg/m3) 1408. 5515. 0.255
Surface gravity (eq.) (m/s2) 274.0 9.78 28.0
Escape velocity (km/s) 617.6 11.19 55.2
Ellipticity 0.00005 0.0034 0.015
Moment of inertia (I/MR2) 0.059 0.3308 0.178
Visual magnitude V(1,0) -26.74 -3.86 -
Absolute magnitude +4.83
Luminosity (1024 J/s) 384.6
Mass conversion rate (106 kg/s) 4300.
Mean energy production (10-3 J/kg) 0.1937
Surface emission (106 J/m2s) 63.29
Spectral type G2 V
Model values at center of Sun:
Central pressure: 2.477 x 1011 bar
Central temperature: 1.571 x 107 K
Central density: 1.622 x 105 kg/m3
Rotational and Orbital
parameters
Sun Earth Ratio (Sun/Earth)
Sidereal rotation period (hrs)* 609.12 23.9345 25.449
Obliquity to ecliptic (deg.) 7.25 23.45 0.309
Speed relative to nearby stars (km/s) 19.4
*This is the adopted period at
16 deg. latitude - the actual rotation rate varies with latitude L as:
( 14.37 - 2.33 sin2 L - 1.56 sin4 L ) deg/day
North Pole of Rotation
Right Ascension: 286.13
Declination : 63.87
Reference Date : 1.5 Jan 2000 (JD 2451545.0)
Sun Observational
Parameters
Apparent diameter from Earth
At 1 A.U.(seconds of arc) 1919.
Maximum (seconds of arc) 1952.
Minimum (seconds of arc) 1887.
Distance from Earth
Mean (106 km) 149.6
Minimum (106 km) 147.1
Maximum (106 km) 152.1
Solar Magnetic Field
Typical magnetic field strengths for various parts of the Sun
Polar Field: 1 - 2 Gauss
Sunspots: 3000 Gauss
Prominences: 10 - 100 Gauss
Chromospheric plages: 200 Gauss
Bright chromospheric network: 25 Gauss
Ephemeral (unipolar) active regions: 20 Gauss
Solar Atmosphere
Surface Gas Pressure (top of photosphere): 0.868 mb
Effective temperature: 5778 K
Temperature at bottom of photosphere: 6600 K
Temperature at top of photosphere: 4400 K
Temperature at top of chromosphere: ~30,000 K
Photosphere thickness: ~400 km
Chromosphere thickness: ~2500 km
Sun Spot Cycle: 11.4 yr.
Photosphere Composition:
Major elements: H - 90.965%, He - 8.889%
Minor elements (ppm): O - 774, C - 330, Ne - 112, N - 102
Fe - 43, Mg - 35, Si - 32, S - 15
The Milky Way
The Sun is a medium size star known
as a yellow dwarf. The Sun is just one of about 100
billion stars in our galaxy, The Milky Way. The Sun is by far the largest object
in the solar system. It contains more than 99.8% of the total mass of the Solar
System . The Sun is about 93 million miles away from the Earth. The distance
from the Earth to the Sun varies throughout the year. At its closest, the Sun is
91.1 million miles from Earth. At its farthest the distance between the Sun and
the Earth is 94.2 million miles. It takes light 8 min. 20 sec to travel from the
sun to the Earth.
The Sun Dwarfs The Planets In Size
The
composite above shows the Sun and the 5 largest planets (Earth is the tiny spot
between Jupiter and the Sun)
The Sun is about 4.5 billion years
old. It will continue to radiate for another 5 billion years. It will
start to run out of core hydrogen in *less* than 4 billion years from now, and
will be expanding into a red giant from that point on. In fact, the energy
output of the sun will increase prior to the red giant phase to a point where
the Earth will probably become too hot to support life in only 1 or 2 billion
years. When the sun does reach the red giant phase, the core will finally become
hot enough for helium fusion to occur (the "Helium flash", followed by
core Helium fusion and continued Hydrogen fusion in a shell around the growing
Helium core). After this Helium in the core is exhausted, the sun will then
collapse into a white dwarf.
The nearest stars to our sun
are:
Proxima Centauri (Alpha Cen C) 4.22
Light years away -39,900,000,000,000 km away
Rigil Kentaurus (Alpha Cen A) 4.35
Light years away
Alpha Centauri (B) 4.35 Light years
away
Barnard's Star 5.9 Light years
away
Wolf 359 7.6 Light years away
A light-year is a unit of
length used by astronomers to measure interstellar distance (the distance
between stars). A light-year is defined as the distance that light will
travel in a year. The speed of light is 186,000 miles per second (300,000 km
per second).
186,000 mi/sec
x 60 sec/min x 60 min/hr x 24 hr/day x 365 days/yr
one light-year
is equal to 9,500,000,000,000 kilometers or 5,865,696,000,000 miles
The Sun is personified in many
cultures: the Greeks called it Helios, the Egyptians principal god was Ra the
sun god and the Romans called it Sol.
Percent
of Sun's
Composition
Element
93.96000%
hydrogen
5.91900%
helium
0.06483%
oxygen
0.03946%
carbon
0.00817%
nitrogen
0.00423%
silicon
0.00376%
magnesium
0.00348%
neon
0.00301%
iron
0.00150%
sulfur
0.00028%
aluminum
0.00019%
calcium
0.00019%
sodium
0.00019%
nickel
0.00009%
argon
The Sun is an average star,
similar to millions of others in the Universe. It is classified as a yellow
dwarf of spectral class G2.
Sunspot Loops
Even a relatively quiet day on the Sun is busy.
This ultraviolet image shows
bright, glowing arcs of gas flowing around the sunspots.
Image Credit: NASA
It is a prodigious energy
machine, manufacturing about 4.0E023 kilowatts of energy per second. In other
words, if the total output of the Sun was gathered for one second it would
provide the U.S. with enough energy, at its current usage rate, for the next
9,000,000 years. The basic energy source for the Sun is nuclear fusion, which
uses the high temperatures and densities within the core to fuse hydrogen,
creating energy and producing helium as a by-product. The core is so dense and
the size of the Sun so great that energy released at the center of the Sun takes
about 50,000,000 years to make its way to the surface, undergoing countless
absorptions and reemissions in the process. The Sun's visible surface, called
the photosphere, has a temperature of 5,700 C(10,900 Degrees F). The gases heat up and become more
compressed at deeper levels, until the temperature reaches 15 million C( 27
Million Degrees F) deep
within the Sun's energy producing core (If the Sun were to stop producing
energy today, it would take 50,000,000 years for the effects to be felt at
Earth!
Layers of the Sun
The Sun, can be divided into six
layers. From the center out, the layers of the Sun are as follows: the solar
interior composed of the core (which occupies the innermost quarter or so of the
Sun's radius), the radiative zone, and the the convective zone, then there is
the visible surface known as the photosphere, the chromosphere, and finally the
outermost layer, the corona. The innermost layer of the sun is the core. With a
density of 160 g/cm^3, 10 times that of lead, the core might be expected to be
solid. However, the core's temperature of 15 million kelvins (27 million degrees
Fahrenheit) keeps it in a gaseous state.
The Core
In the core, fusion reactions
produce energy in the form of gamma rays and neutrinos. Gamma rays are photons
with high energy and high frequency. The gamma rays are absorbed and re-emitted
by many atoms on their journey from the envelope to the outside of the sun. When
the gamma rays leave atoms, their average energy is reduced. However, the first
law of thermodynamics (which states that energy can neither be created nor be
destroyed) plays a role and the number of photons increases. Each
high-energy gamma ray that leaves the solar envelope will eventually become a
thousand low-energy photons.
The neutrinos are extremely
nonreactive. To stop a typical neutrino, one would have to send it through a
light-year of lead! Several experiments are being performed to measure the
neutrino output from the sun. Chemicals containing elements with which neutrinos
react are put in large pools in mines, and the neutrinos' passage through the
pools can be measured by the rare changes they cause in the nuclei in the pools.
For example, perchloroethane contains some isotopes of chlorine with 37
particles in the nucleus (17 protons, 20 neutrons). These Cl-37 molecules can
take in neutrinos and become radioactive Ar-37 (18 protons, 19 neutrons). From
the amount of argon present, the number of neutrinos can be calculated.
Solar Envelope
Outside of the core is the
radiative envelope, which is surrounded by the convective envelope. The
temperature is 4 million kelvins (7 million degrees F). The density of the solar
envelope is much less than that of the core. The core contains 40 percent of the
sun's mass in 10 percent of the volume, while the solar envelope has 60 percent
of the mass in 90 percent of the volume.
The solar envelope puts pressure
on the core and maintains the core's temperature.
The hotter a gas is, the more
transparent it is. The solar envelope is cooler and more opaque than the core.
It becomes less efficient for energy to move by radiation, and heat energy
starts to build up at the outside of the radiative zone. The energy begins to
move by convection, in huge cells of circulating gas several hundred kilometers
in diameter. Convection cells nearer to the outside are smaller than the inner
cells. The top of each cell is called a granule. Seen through a telescope,
granules look like tiny specks of light. Variations in the velocity of particles
in granules cause slight wavelength changes in the spectra emitted by the sun.
Photosphere
The photosphere is the zone
from which the sunlight we see is emitted. The photosphere is a comparatively
thin layer of low pressure gasses surrounding the envelope. It is only a few
hundred kilometers thick, with a temperature of 6000 K. The composition,
temperature, and pressure of the photosphere are revealed by the spectrum of
sunlight. In fact, helium was discovered in 1896 by William Ramsey, when in
analyzing the solar spectrum he found features that did not belong to any gas
known on earth. The newly-discovered gas was named helium in honor of Helios,
the mythological Greek god of the sun.
Chromosphere
In an eclipse, a red circle
around the outside of the sun can sometimes can be seen. This is the
chromosphere. Its red coloring is caused by the abundance of hydrogen.
From the center of the sun to the
chromosphere, the temperature decreases proportionally as the distance from the
core increases. The chromosphere's temperature, however, is 7000 K, hotter than
that of the photosphere. Temperatures continue to increase through the corona.
Sunspots
Large
sunspot group -- Active region 9169
Sunspots are dark spots on
the photosphere, typically with the same diameter as the Earth. They have cooler
temperatures than the photosphere. The center of a spot, the umbra, looks dark
gray if heavily filtered and is only 4500 K (as compared to the photosphere at
6000K). Around it is the penumbra, which looks lighter gray (if filtered).
Sunspots come in cycles, increasing sharply (in numbers) and then decreasing
sharply. The period of this solar cycle is about 11 years.
The sun has enormous organized
magnetic fields that reach from pole to pole. Loops of the magnetic field oppose
convection in the convective envelope and stop the flow of energy to the
surface. This results in cool spots at the surface which produce less light than
the warmer areas. These cool, dark spots are the sunspots.
Corona
The outermost layer of the
sun is the corona. Only visible during eclipses, it is a low density cloud of
plasma with higher transparency than the inner layers. The white corona is a
million times less bright than the inner layers of the sun, but is many times
larger.
The corona is hotter than some of
the inner layers. Its average temperature is 1 million K (2 million degrees F)
but in some places it can reach 3 million K (5 million degrees F).
Temperatures steadily decrease as
we move farther away from the core, but after the photosphere they begin to rise
again. There are several theories that explain this, but none have been proven.
The Great Conveyor
Belt is a massive circulating current of fire (hot plasma) within the sun. It
has two branches, north and south, each taking about 40 years to complete one
circuit. Researchers believe the turning of the belt controls the sunspot cycle.
The center of the Sun
The center of the
sun is very hot (about 15 million degrees Celsius) and the pressure is immense
(about 100 billion times the airpressure here on Earth). Because of that, atoms
come so close to eachother that they fuse.
In every second, the
Sun spends 700 billion tons of protons (or: Hydrogen) in this way. And only a
small fraction (0.7 percent) is turned into light. Right now, about half of the
amount of Hydrogen in the core of the Sun has been fused into Helium.
Solar
Cycle
The
Schwabe solar cycle or Schwabe-Wolf cycle is the eleven-year cycle of solar
activity of the sun.
It
was named after Samuel Heinrich Schwabe (October 25, 1789 April 11, 1875) a
German astronomer remembered for his work on sunspots. At periods of highest
activity, known as solar maximum or solar max, sunspots appear. Periods of
lowest activity are known as solar minimum. The last solar maximum was in 2001.
The solar cycle is not strictly 11 years; it has been as short as 9 years and as
long as 14 years in recent years.
It
is followed by a period of quiet called the "solar
minimum".
Comet
NEAT and a CME in LASCO C3
During the solar maximum there are many sunspots, solar flares,
and coronal mass ejections, all of which can affect communications and weather
here on Earth.
