sun properties

1. Our Star, the Sun

2. The Sun: Our Star
A glowing ball of gas
held together by its
own gravity and
powered by nuclear
fusion

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Radius: 700,000 km (435,000 miles)
Diameter: 1.392 million km (865,000 miles)
Circumference: 4.4 million km (2.7 million miles)
Mass: 2.0 × 1030 kg (In lbs that would be 4.4 w/ 30 zeros!)
Density: 1400 kg/m3 (3,080 lbs/m³ or 1.4 g/cm³ or 1.4 times that of water)
about ¼ the earth’s density, similar to the Jovian planets
Rotation: We use sunspots to determine. Differential (faster at the equator
(25 days), slower at the poles (31 days at 6°degree latitude); period about
a month
Core Temp: 27 million°F
Surface Temp: 10,000°F (5,800°K - above melting point of any known
material)
Apparent surface of Sun is photosphere –not a solid surface
Physical Properties of
the Sun

4. The Sun is the Largest Object in
the Solar System
• The Sun contains more than 99.85% of the
total mass of the solar system
• If you put all the planets in the solar system,
they would not fill up the volume of the Sun
• 110 Earths or 10 Jupiters fit across the
diameter of the Sun
How big is the Sun?

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Let’s reduce the size of the solar system by a factor of
10 billion; the Sun is now the size of a large grapefruit
(14 cm diameter).
How big is Earth on this scale?
A. an atom
B. the tip of a ballpoint pen
C. a marble
D. a golf ball

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The scale of the solar system
• On a 1-to-10 billion
scale:
—Sun is the size of a
large grapefruit (14
centimeters).
— Earth is the size of a
tip of a ballpoint pen,
15 meters away.
Relative Distance of the Nearest Star

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Scales and Sizes In Astronomy
• Mercury’s distance from the Sun.
• Is about half the Sun-Earth distance.
• It is half an Astronomical Unit.
• The star Sirius is about twice as massive as the Sun
• We say it has a mass of two solar masses.
• Sirius is about 25 times more luminous than the Sun.
• We say it has a luminosity of twenty-five solar luminosities.

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SOHO: Eavesdropping on the Sun
SOHO: Solar and Heliospheric
Observatory
Orbits at Earth’s L1 point,
outside the magnetosphere
Multiple instruments measure
magnetic field, corona,
vibrations, and ultraviolet
emissions

10. Sunspots
What are they?
What do they do to us?
Why should you even care?

11. What is a sunspot
 Sunspots are temporary phenomena on the
photosphere of the Sun that appear visibly as
dark spots compared to surrounding regions.
They are caused by intense magnetic activity
that draws off the convection of heat to the
surface, thus cooling the surface.
 Sunspots are usually in pairs because of the
magnetic activity causing North and South
poles at either of the spots.
Pic on next slide

12. NASA Image of sunspots,
September, 2011

13. What do sunspots do to us?
 Sunspots are a main hotbed of solar flares and
prominences from the sun.
 These are in turn pushed by their energy into
space as solar wind once they break free of
the sun's gravity
 These solar winds are comprised of highly
charged particles hurtling towards Earth

14. Sunspot projecting a flare into space

15. What does that mean to you?
 All of those charged particles will wreak havoc with
electronics. A particularly large solar flare caused
blackouts over a large portion of Canada.
 The particles can also cause the Aurora Borealis over
the northern latitudes, known as the Northern Lights.
 On a darker note this can also cause massive
disruptions to communications, GPS, and military
satellites. So if a bad solar storm were to hit, it could
potentially cut off your phone from Facebook, cause
your car to get wrong directions, and make the Air
Force shoot a missile at the wrong building.

16. What happens with a solar flare.

17. Watch Youtube Video:
Whats a Solar Flare or CME and
WHY are they dangerous?

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Day 2 Notes

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Physical Properties of
the Sun
This is a filtered image of the Sun showing sunspots, the
sharp edge of the Sun due to the thin photosphere, and the
corona

20. The Active Sun
1. Sunspots
appear dark because they are cooler areas
they have a regular 11 year cycle
2. Prominences
Huge cloudlike structures of chromatic gases
trapped by magnetic fields
3. Solar flares
sudden brightening above a sunset cluster
Auroras-display of color near poles caused by
solar flares

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What is the Sun Made of?

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Interior structure of the
Sun: The core is where
nuclear fusion takes place
The photosphere is the
visible “surface” of the
Sun. Below it lie the
convection zone, the
radiation zone, and the
core. Solar atmosphere
consists of the
chromosphere, the
transition zone
(temperature rises
dramatically), and the
corona.

23. Convection zone and Radiation
zone
• Convection
-Below photosphere where the material
is in constant convective motion
• Radiation
– Solar energy is transported due to radiation

24. Photosphere
• Grainy appearance to sun when look in a
telescope caused by granules, areas of
hotter gases rising—last 10 minutes and
new ones arise causing a convection
• 90% of sun’s surface are hydrogen
• 10% helium

25. Chromosphere
Above the photosphere is a thin layer of hot
gases. It is viewed during an eclipse as a
thin red rim

26. Corona
Outermost portion of the atmosphere
Visible only when photosphere is covered
Solar wind—ionized gases that escape the
gravitational pull of the sun and bombard
parts of solar system, it can effect our
atmosphere.

27. The Solar Interior
Nuclear Fusion
-Converts four Hydrogen nuclei into one
helium releasing energy
energy is released because some matter is
converted to energy
Causes the core to grow in size
Sun can exist in its present state another 10
billion years

28. • Nuclear fusion in the sun is a process by
which rapidly colliding nuclei, like those of
hydrogen and helium, fuse together at
very high temperatures, to form nuclei of
higher atomic weight.
• Nuclear fusion in the sun is a merger of
smaller nuclei into heavier ones, releasing
a lot of energy in the process.
What is nuclear fusion in the sun?

29. How it works!
• In the process of the hydrogen and helium
fusing together, some mass is lost and
converted into energy.
• Nuclear fusion in the sun is only possible
when the repulsion between protons is
overcome.
– For that to happen, energy and temperature
at the suns core has to be really high.

30. The Suns core
• The total radius of the sun is 6.955 x 10^5
km (about 109 times the radius of Earth)
– Its core extends from the center to about 1.8
km, with a temperature of 14.5 million Kelvin.

31. • Consider that four hydrogen atoms have a combined
atomic mass of 4.032 atomic mass units whereas the
atomic mass of helium is 4.003 atomic mass units, or
0.029 less than the combined mass of hydrogen. The
tiny missing mass is emitted as energy as according to
Einstein's equation:
E=mc^2
• E equals energy, m equals mass, and c equals the
speed of light. Because the speed of light if very great
(300,000 km/s), the amount of energy released from
even a small amount of mass is enormous.

32. • The conversion of just one pinheads worth of hydrogen
to helium generates more energy than burning thousand
of tons of coal.
• The sun is consuming an estimated 600 million tons of
hydrogen each second; about 4 million tons are
converted to energy.
– Even at the enormous rate of consumption, the sun
has enough fuel to last easily another 100 billion
years.
– However, evidence from other stars indicates that the
sun will grow dramatically and engulf Earth long
before all of its hydrogen is gone.
– It is thought that a star the size of the sun can exist in
its present state for 10 billion years.

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Day 3 notes

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Luminosity—total energy radiated by the Sun— can be
calculated from the fraction of that energy that reaches Earth.
Solar constant—amount of Sun's energy reaching Earth—is
1400 W/m2. (W = watts)
Total luminosity is about 4 × 1026 W—the equivalent of 10
billion 1-megaton nuclear bombs per second.
Physical Properties of
the Sun

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We can draw an imaginary
sphere around the Sun so that
the sphere’s surface passes
through Earth’s center. The
radius of this imaginary sphere
equals 1 AU. The “solar
constant” is the amount of
power striking a 1-m2 detector
at Earth’s distance. By
multiplying the sphere’s surface
area by the solar constant, we
can measure the Sun’s
luminosity—the amount of
energy it emits each second.
Solar Luminosity

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Doppler shifts of solar spectral lines indicate a complex
pattern of vibrations

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Solar Oscillations
(a) The Sun has been found to vibrate in a very
complex way. By observing the motion of the
solar surface, scientists can determine the
wavelength and the frequencies of the
individual waves and deduce information about
the solar interior not obtainable by other means.
The alternating patches represent gas moving
down (red) and up (blue).
(b) (b) Depending on their initial directions, the
waves contributing to the observed oscillations
may travel deep inside the Sun, providing vital
information about the solar interior. (National
Solar Observatory)

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Solar
density and
temperature
, according
to the
standard
solar model

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Sunspots come
and go, typically
in a few days.
Sunspots are
linked by pairs of
magnetic field
lines.
Solar Magnetism

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Solar Magnetism
Sunspots originate when magnetic field lines are
distorted by Sun’s differential rotation

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The Sun has an 11-year sunspot cycle, during which
sunspot numbers rise, fall, and then rise again
Solar Magnetism

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This is really a 22-year cycle, because the spots switch
polarities between the northern and southern hemispheres
every 11 years
Maunder minimum: few, if any, sunspots
Solar Magnetism

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Solar Convection
Physical transport of energy in the Sun’s convection zone. We
can visualize the upper interior as a boiling, seething sea of
gas. Each convective loop is about 1000 km across. The
convective cell sizes become progressively smaller closer to the
surface.

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Solar Granulation
Typical solar granules are
comparable in size to
Earth’s continents. The
bright portions of the
image are regions where
hot material is upwelling
from below. The dark
regions correspond to
cooler gas that is sinking
back down into the
interior.

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Solar Spectrum A
detailed spectrum of
our Sun shows
thousands of
Fraunhofer spectral
lines which indicate
the presence of
some 67 different
elements in various
stages of excitation
and ionization in the
lower solar
atmosphere. The
numbers give
wavelengths, in
nanometers.
(Palomar
Observatory/Caltech)

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What are Neutrinos?
Neutrinos are subatomic particles produced by the decay of
radioactive elements and are elementary particles that lack
an electric charge
Neutrinos are emitted directly from the core of the Sun and
escape, interacting with virtually nothing. Being able to
observe these neutrinos would give us a direct picture of what
is happening in the core. Unfortunately, they are no more
likely to interact with Earth-based detectors than they are with
the Sun;
Observations of Solar
Neutrinos

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16.7 Observations of Solar
Neutrinos
Typical solar neutrino detectors; resolution is very poor

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• Main interior regions of Sun: core, radiation zone, convection
zone, photosphere, chromosphere, transition region, corona, solar
wind
• Energy comes from nuclear fusion; produces neutrinos along
with energy
•Study of solar oscillations leads to information about interior
•Absorption lines in spectrum tell composition and temperature
• Sunspots associated with intense magnetism
• Number of sunspots varies in an 11-year cycle
• Large solar ejection events: prominences, flares, and coronal
ejections
Summary of the sun