Unit 15, Table 2 By: Carlos Monsante, Emily Watkins, Ryan Barker

WWK Students will know the evidence and current theories concerning the evolution of the universe.

At First… Based on what we know about the universe about 14 billion years ago there was no universe, no stars, nothing. Then in an instant a small condensed point in space, containing all the matter in the universe, exploded. This event is known as the big bang. Due to the enormous explosion the universe and the stars are still moving a part from each other this process is called red shift. Our sun is only about 4 or 5 billion years old.

Universal Time On Earth we tell time by how the Earth spins on its axis on an orbit around the sun. This way of telling time is called universal time or solar time. It takes the Earth about days to move around our sun. Because of the extra one quarter of a day, every four years there is a leap day.

Sidereal Time Sidereal time is a method used by astronomers to know where to point there telescopes in the sky to look at a specific star. Because the Earth is spinning the position of the star is slightly different every sidereal day. Which is how much the position of the star has moved. As we tell time based on Earths axis spin fixed around our sun this way of telling time is Earth fixed around simply a different star.

KS How often is there a leap day?

WWK Students will know a star’s structure and how it aides nuclear fusion.

Structure At the center of stars is the core. The core is where nuclear fusion occurs. The temperature of our sun’s core is about 27,000,000°F or 15,000,000°C. The next layer of stars is the convection zone. The convection zone is made of less dense material which allows it to move the energy released through nuclear fusion in the core to the outer layers of the stars. This zone facilitates the transference of energy to the rest of the universe.

Structure Cont’d. The next level of stars is the photosphere, a shallow section that projects the star’s light. The chromosphere is where many solar flares erupt. Finally, the last layer is the corona. The corona is where the solar winds are which are caused by the out-flowing of energy.

Nuclear Fusion The entire structure of stars make the giant nuclear reactors. Stars use nuclear fusion to produce energy and to fuel themselves. Nuclear fusion only occurs in the core of stars and is a process where atomic nuclei are fused to from a heavier nucleus. Nuclear fusion is an exothermic reaction in which energy is released primarily as heat.

Types of Nuclear Fusion One type of nuclear fusion is a proton-proton chain. A proton-proton chain is the cycle of nuclear fusion where hydrogen atoms fuse to form helium. Another type of nuclear fusion is the CNO cycle. The CNO cycle, or carbon-nitrogen-oxygen cycle, is the type nuclear fusion that older and therefore larger massed stars use. Because older stars have used up most of their hydrogen at a certain time, they have to replace the proton-proton chain and use produce carbon, nitrogen and oxygen instead of hydrogen.

Energy Transfer Energy released through nuclear fusion must then find a way to go to the outer edges of the star and then to the rest of the universe. This is where the convection zone comes into play. The convection zone is made up of materials that aren’t as dense as the core is which allows the materials to move more freely. As energy emanates from the core, the zone picks up the energy and provides a medium for it to cycle through much in the same way a convection oven works. Once the energy is transferred to the photosphere, the materials cycle back around to the core to pick up more energy. The photosphere’s shallowness allows for the energy to flow quickly into the chromosphere and then into the corona. After leaving the star, the energy radiates at high speeds, a.k.a. light speed, until it travels to the planetary bodies that it reaches.

Relevancy of This to Us In essence, without the structure of stars, particularly ours, being the way it is, we wouldn’t have the energy for anything to grow. Without growth of crops, animals wouldn’t have a food source so there wouldn’t be any animals to eat either. As omnivores, people would have nothing of which to provide us sustenance and therefore, we would die if we lived at all. So, that my friends, is why we should be happy with our lovely sun and all the stars out there in the universe and the fact that they are giant nuclear reactors.

K.S. Which process of nuclear fusion combines hydrogen to make helium?

Video Time Video

 Students will know and understand the life cycle of stars.

 A protostar is a cloud of interstellar gas and dust that gradually collapses, forming a hot dense core, on evolves into a star once nuclear fusion can occur in the core.  Average Lifespan: 100,000 years.

 The next step in the life cycle of a star is known as the Main Sequence.  A Main Sequence star is a star that occupies a continuous distinctive band formed by plotting stellar color versus brightness for a large sample of stars.  Average Lifespan: 10 billion years.

 After the Main Sequence, comes the Red Giant.  A Red Giant is the phase near the end of a stars lifecycle when the star starts to convert helium to produce life. The helium sinks to the center of the star, with a shell of hydrogen around the helium core. As the star collapses, the pressure and temp. rise until it is high enough for helium to fuse to carbon, i.e. helium burning begins. to radiate the energy produced by the helium burning, the star expands into a Red Giant.  Average Lifespan: about 14 million years.

 After the Red Giant expands one of two things happen. It implodes and either a White Dwarf star or a Black Hole will be created.  A White Dwarf star is the aftermath of a Red Giant. After a star exhausts all of it nuclear fuel, it implodes and creates a White Dwarf. Near the end of its nuclear burning stage, this type of star expels most of its outer material, creating a planetary nebula. This star burns at approximately 100,000 Kelvin.  Average Lifespan: as long as 10^200 years or as short as a few hundred thousand.

 The other option, after the collapse of a Red Giant, is a Black Hole.  A Black Hole is formed when a star collapses, with most or all of its mass compressed into a sufficiently small area of space, causing infinite space-time singularity, a bending at a point. Because of its size of singularity nothing, not even light, is able to escape the “event horizon.”  Average lifespan: Approximately 1.2x10^67 years.

 What is the third stage of a stars life cycle?

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