Chapter 29 and 30
Explain how the sun converts matter into energy in its core. Describe the three layers of the sun s atmosphere. Explain how sunspots are related to powerful magnetic fields on the sun. Describe how the solar wind can cause auroras on Earth.
Using a device called a spectrograph, scientists break up the sun s light into a spectrum. Dark lines form in the spectra of stars when gases in the stars outer layers absorb specific wavelengths of the light that passes through the layers. By studying the spectrum of a star, scientists can determine the amounts of elements that are present in a star s atmosphere.
Both hydrogen and helium are found in the sun About 75% of the sun s mass is hydrogen, and hydrogen and helium together make up about 99% of the sun s mass. The sun s spectrum reveals that the sun contains traces of almost all other chemical elements.
nuclear fusion the process by which nuclei of small atoms combine to form a new, more massive nucleus; the process releases energy Nuclear fusion occurs inside the sun. Nuclei of hydrogen atoms are the primary fuel for the sun s fusion. Nuclear fusion produces most of the suns energy and consists of three steps.
1.) two hydrogen nuclei, or protons, collide and fuse. the positive charge of one of the protons is neutralized as that proton emits a particle called a positron. As a result, the proton becomes a neutron and changes the original two protons into a protonneutron pair.
2.) another proton combines with this protonneutron pair to produce a nucleus made up of two protons and one neutron. 3.) two nuclei made up of two protons and one neutron collide and fuse. As this fusion happens, two protons are released. The remaining two protons and two neutrons are fused together and form a helium nucleus. At each step, energy is released.
The energy released during the three steps of nuclear fusion causes the sun to shine and gives the sun its high temperature
sun s energy comes from fusion, and the mass that is lost during fusion becomes energy. In Einstein s equation E = mc 2 E = energy produced; m = mass; and c = speed of light (300,000 km/s) used to calculate the amount of energy produced from a given amount of matter. Using E = mc 2 astronomers were able to explain the huge quantities of energy produced by the sun.
The parts of the sun include the core, radiative zone, and convective zone. At the center of the sun is the core. The core makes up 25% of the sun s total diameter of 1,390,000 km. The temperature of the core is about 15,000,000 kmºc. The core is made up entirely of ionized gas, and is 10 times as dense as iron.
radiative zone located between the core and convective zone; energy moves by radiation The temperature of the radiative zone ranges from about 2,000,000ºC to 7,000,000 ºC. In the radiative zone, energy moves outward in the form of electromagnetic waves, or radiation.
Convective zone region of sun s interior between the radiative zone and the photosphere and in which energy is carried upward by convection The convective zone surrounds the radiative zone. The temperature of the convective zone is about 2,000,000ºC. Energy produced in the core moves through this zone by convection. Convection is the transfer of energy by moving matter.
surrounds the convective zone Because the sun is made of gases, the term atmosphere refers to the uppermost region of solar gases The sun s atmosphere has three layers: Photosphere- inner Chromosphere- middle Corona- outer
photosphere the visible surface of the sun Photosphere means sphere of light. The photosphere is made of gases that have risen from the convective zone. The temperature in the photosphere is about 6,000ºC. Much of the energy given off from the photosphere is in the form of visible light.
chromosphere thin layer of sun above the photosphere and that glows a reddish color during eclipses The chromosphere s temperature ranges from 4,000 C to 50,000 C. The gases of the chromosphere move away from the photosphere, forming narrow jets of hot gas that shoot outward and then fade away within a few minutes.
corona the outermost layer of the sun s atmosphere The corona is a huge region of gas that has a temperature above 1,000,000ºC. As the corona expands, electrons and electrically charged particles called ions stream out into space. These particles make up solar wind, which flows outward from the sun to the rest of the solar system.
sunspot a dark area of the photosphere of the sun that is cooler than the surrounding areas and has a strong magnetic field. movements of gases within convective zone and the movements caused by the sun s rotation produce magnetic fields. These magnetic fields cause convection to slow in parts creating sunspots. Observations of sunspots have shown that the sun rotates. rotates once every 27 days at the equator, but only once in 31 days at the poles.
The solar-activity cycle is caused by the changing solar magnetic field and releases solar ejections Solar ejections are events in which the sun emits atomic particles Prominences Solar Flares Coronal Mass Ejections
Prominances - arches of glowing gases that follow the curved lines of the magnetic force from a region of one magnetic force to a region of the opposite magnetic polarity. solar flare most violent, an explosive release of energy (from sunspots)that comes from the sun associated with magnetic disturbances on the sun s surface coronal mass ejection coronal gas and particles of solar flare thrown into space from the sun increasing the strength of the solar wind. cause disturbances to Earth s magnetic field.
aurora colored light produced by charged particles from the solar wind and magnetosphere that react with and excite the oxygen and nitrogen of Earth s upper atmosphere usually seen in the sky near Earth s magnetic poles. Auroras are the result of the interaction between the solar wind and Earth s magnetosphere.
star - a large celestial body that is composed of gas and that emits light. Stars are made up of different elements in the form of gases. All stars have dark-line spectra that reveals the star s composition and temperature. most common element in stars is hydrogen Helium is second most common Small quantities of carbon, oxygen, and nitrogen are also present
The temperature of most stars ranges from 2,800 C to 24,000 C. Blue stars have average surface temperatures of 35,000 C. Yellow stars, such as the sun, have surface temperatures of about 5,500 C. Red stars have average surface temperatures of 3,000 C.
Stars vary in size and mass. Stars such as the sun are considered mediumsized stars. The sun has a diameter of 1,390,000 km. Most stars visible from Earth are medium-sized stars. Many stars also have about the same mass as the sun, however some stars may be more or less massive.
apparent motion of stars is the motion visible to the unaided eye is caused by the movement of Earth. The rotation of Earth causes the apparent motion of stars to seem to move counterclockwise around the North Star. Earth s revolution around the sun causes the stars to appear to shift slightly to the west every night.
Some stars are always visible in the night sky. These stars never pass below the horizon. In the Northern Hemisphere, the movement of these stars makes them appear to circle the North Star. These circling stars are called circumpolar stars.
Most stars have several types of actual motion. Stars rotate on an axis. Some stars may revolve around another star. Stars either move away from or toward our solar system. Distance from Earth usually measured in light-years Doppler effect - an observed change in the frequency of a wave when the source or observer is moving Blue shift- toward earth Red shift away from earth
Apparent magnitude - the brightness of a star as seen from the Earth. The apparent magnitude of a star depends on both how much light the star emits and how far the star is from Earth. Absolute magnitude - how much light the star actually gives off if distance wasn t an issue
astronomers discovered a relationship between the absolute magnitude (real brightness) of a star and its surface temperature. They plotted the data on a graph called Hertzsprung-Russell (H-R) The graph shows grouping of stars, with majority of stars making a diagonal Observed stars moved through these groupings as time passes Determined star life cycle
So what does this show? Stars seemed to naturally group together
Nebula- a large cloud of gas and dust in interstellar space; a region in space where stars are born. A star beings in a nebula. When the nebula is compressed, some of the particles move close to each other and are pulled together by gravity. (this makes a star) As gravity makes dense regions within a nebula more compact, these regions spin and shrink forming a protostar. protostar increase in temperature for several million years. Eventually the gas becomes so hot its electrons are stripped from their parent atoms creating plasma
A protostar s temperature continually increases until it reaches about 10,000,000 C At this temperature nuclear fusion starts Nuclear fusion marks the birth of a star it can continue for billions of years.
The second and longest stage in the life of a star is the main-sequence stage. During this stage, energy continues to be generated in the core of the star as hydrogen fuses into helium. A star that has a mass about the same as the sun s mass stays on the main sequence for about 10 billion years. Scientists estimate that over a period of almost 5 billion years, the sun has converted only 5% of its original hydrogen nuclei into helium nuclei.
giant -a very large and bright star whose hot core has used most of its hydrogen. A star enters its third stage when almost all of the hydrogen atoms within its core have fused into helium atoms. A star s shell of gases grows cooler as it expands. As the gases in the outer shell become cooler, they begin to glow with a reddish color. These stars are known as giants.
Planetary Nebulas As the star s outer gases drift away, the remaining core heats these expanding gases. The gases appear as a planetary nebula, a cloud of gas that forms around a sunlike star that is dying.
As a planetary nebula disperses, gravity causes the remaining matter in the star to collapse inward. The matter collapses until it cannot be pressed further together. A hot, extremely dense core of matter - a white dwarf - is left. shine for billions of years before they cool completely. The gases appear as a planetary nebula, a cloud of gas that forms around a sunlike star that is dying.
We are now here Life cycle of our sun
nova - a star that suddenly becomes brighter Some white dwarfs revolve around red giants. When this happens, the gravity of the white dwarf may capture gases from the red giant. As these gases accumulate on the surface of the white dwarf, pressure begins to build up. This pressure may cause large explosions. These explosions are called novas.
A white dwarf may also become a supernova, which is a star that has such a tremendous explosion that it blows itself apart. The explosions of supernovas completely destroy the white dwarf star and may destroy much of the red giant.
This diagram follows the life of both large and average stars.
Main-sequence stars that are more massive than the sun will become larger than giants in their third stage. These highly luminous stars are called supergiants. These stars appear along the top of the H-R diagram.
Massive stars become supernovas as part of their life cycle. After the supergiant stage, the star collapses, producing such high temperatures that nuclear fusion begins again. When nuclear fusion stops, the star s core begins to collapse under its own gravity. This causes the outer layers to explode outward with tremendous force.
neutron star - a star that has collapsed under gravity to the point that the electrons and protons have smashed together to form neutrons Stars more massive than the sun do not become white dwarfs. After a star explodes as a supernova, the core may contract into a neutron star.
Pulsar - a rapidly spinning neutron star that emits pulses of radio and optical energy Some neutron stars emit a beam of radio waves that sweeps across space and are detectable here on Earth. These stars are called pulsars. For each pulse detected on Earth, we know that the star has rotated within that period.
black hole - an object so massive and dense that even light cannot escape its gravity Some massive stars produce leftovers too massive to become a stable neutron star. These stars contract, and the force of the contraction leaves a black hole.