Download 3 - MrFuglestad

Chapter 30 REVIEW
Name
Date
Period
Objective: Know the structure and composition of stars.
1. Stars are made up mostly of what two elements?
Hydrogen and Helium
Objective: Know what spectra are, and how they are used.
2. How do Astronomers know what elements are in a star?
Spectra are a unique light emissions or absorptions for each element.
When Astronomers look at the light coming from a star they analyze it using a spectrometer . This analysis
tells them the elements that the star is made of by comparing it to known spectra for a given element.
Objective: Describe the solar activity cycle and how it affects Earth.
3.What is the solar wind?
Ions and other particles emitted from the Sun
4. How are the northern lights formed?
1) Molecules in our upper atmosphere absorb charged particles that are streaming from the Sun in the
solar wind.
2) The electrons in those molecules become excited and move to the next highest energy level when they
absorb one of these charged particles.
3) Eventually they go back to their lower energy level, which releases the energy in the form of a photon
(visible light)
Oxygen makes a yellowish-green or red
Nitrogen makes the color red most often
Hydrogen and Helium make blue and purple but are often hard to see.
(This is the same thing that happens in a neon sign)
4) These lights dance across the sky in the upper atmosphere as the Earth’s magnetic field catches and
directs the charged particles in solar wind to the far north and far south of our planet.
Increased Sun activity makes for periods of more intense northern and southern lights.
Occasionally during these periods of high activity they can be seen farther south at our latitude.
5. What is nuclear fusion?
Nuclear fusion is the process where atoms of elements are fused together under intense pressure and
heat to form heavier elements. During that process some of the matter is converted to energy and is
released. This process allows sends and enormous amount of energy as a relatively steady fl ow.
Objective: Be able to classify a star by reading an H-R diagram.
6. Look at the H-R diagram in your book on page 819. What temperature range (from low to high) do
yellow stars occupy?
Approximately 6,000 – 9,000 degrees Kelvin.
7. What is the relationship between the temperature of a star and the color light (wavelength and energy)
that it produces?
Higher temperature stars are shifted toward blue light (higher energy and shorter wavelength)
Lower temperature starts are shifted toward red light (lower energy and longer wavelength)
8. What color are the hottest stars?
The hottest stars are blue. The coolest are red.
Objective: Know the life cycle of a star and be able to describe the evolution of a star at each
stage.
9. List the stages in a stars life cycle. Give a brief description of what occurs at each stage.
Nebula – A massive cloud of dust and gas where stars are born. Most of the gas in this cloud is
Hydrogen. Hydrogen is the most abundant element in the Universe (estimated 73%), wi th Helium
composing around 25% of the remainder.
Protostar – Particles clump together in a rotating disk with a star forming at its center. These particles are
attracted to each other by gravity. Everything that has mass in the Universe is attracted to other objects
by gravity.
Nuclear fusion – The protostar attracts more material and eventually has enough density and temperature
in the center for fusion to begin. The first reaction is Hydrogen fused together to form Helium. As the
percentage of Helium goes up the percentage of Hydrogen goes down.
Main sequence – The star converts its fuel through fusion into heavier elements and energy. Most stars
fall in the main sequence area of the H-R diagram. Know how to read the diagram.
Red Giant – Hydrogen fusion ends in the core, but continues in a layer just outside the Helium core. The
outer layers of the star expand because the area of Hydrogen being fused pushes the outer layers out.
These outer layers cool and become less luminous. Therefore there is a change in size and color for the
star. Helium in the core may continue to fuse to become Carbon during this stage depending on the stars
mass.
Larger mass stars can become Red Giants several times over the course of their lifetimes as each sourc e
of fuel is used up. The star expands and then pressure in the core “ignites” the next element in the
succession of fusion from Hydrogen to Iron.
Stars that end up with mass less than 1.5 times our Sun’s mass
White Dwarf – Earth sized star that is stable with no nuclear reactions and is made of helium or carbon
depending on the mass. Less massive than our Sun = Helium. There can be other elements present such
as Oxygen, etc. Often the White Dwarf stars are surrounded by nebula.
Black Dwarf – This star is a white dwarf that has cooled down to the point where it no longer emits light.
Nebula – The life cycle of the star starts all over again as clouds of dust and gas recycle star material into
new stars.
Stars that end up with a mass between 1.5 to 3.0 times the mass of our Sun
Neutron star – If a star ends up with a mass greater than 1.5 times our Sun it’s electrons and protons fuse
together at the core to from neutrons under immense pressure. This happens after all the material has
reacted to form Iron. At that point where the star is collapsing in on itself (because of the lack of outward
pressure from fusion) the core becomes only neutrons.
Supernovae – If a neutron star continues to have gases falling inward toward its core as it collapses it
violently explodes.
Stars that end up with a mass greater than 3.0 times the mass of our Sun
Black Hole - If a star is super massive a neutron star never forms because the pressure from inward
falling material is too great. It becomes a Black Hole. This an area in space that appears dark becomes it
does not emit any electromagnetic radiation (light). If any objects get near it they are “sucked in” by its
gravity.
Astronomers believe that the center of our Milky Way galaxy is a Black hole.