Term
| What is the shape of the Milky Way Galaxy? |
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Definition
| A huge, slowly revolving disk. |
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Term
| How can we determine the true size of the Milky Way Galaxy? |
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Definition
| We can determine the true size of the Milky way by mapping where the globular clusters lay b/c they are so luminous that we can see whether or not they are above or below the dense disk of the Milky Way. |
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Term
| What are the THREE main parts of the Milky Way Galaxy? |
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Definition
| Disk, halo, and bulge. A disk about 30-40 kiloparsecs in diameter, a more spherically distributed component called the halo, and a flattened, somewhat elongated bulge of stars at its center. Within the disc, numerous bright young stars collect into spiral arms that wind outward from near the center. |
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Term
| What type of material do we find in each region of the Milky Way Galaxy? |
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Definition
| 15% of the disk's mass made of huge clouds of gas and dust. The core of our galaxy contains a dense swarm of stars and gas as well as a supermassive black hole. |
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Term
| Where do we find the youngest stars in the Milky Way Galaxy? |
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Definition
| Young stars, gas, and dust are found close to the plane of the disk. |
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Term
| Where do we find the oldest stars in the Milky Way Galaxy? |
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Definition
| Older stars span a much larger range of distances from the plane, extending up to several kiloparsecs. |
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Term
| What are the differences b/w Pop I stars and Pop II stars? |
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Definition
PopI stars are young, typically less than a few billion years old, and many of them are blue. They lie in the plane of the galaxy's disk.
PopII stars are generally red and old - more than about 10 billion years old. They lie in the bulge and halo of the galaxy. |
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Term
| How do we determine the mass of the Milky Way Galaxy? |
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Definition
| Astronomers can calculate the Milky Way's mass from the gravitation attraction needed to hold the Sun and other stars in orbit. This is yet another application of Newton's law of graviation. |
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Term
| How was the existence of galaxies other than the Milky Way discovered? |
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Definition
| The studies of external galaxies began in the 18th century when the French astronomer CHarles Messier accidentally discovered many galaxies during his searches for new comets. He realized that some of the faint, diffuse patches of light never moved; so to avoid confusing them with comets, he assigned them numbers and made a catalog of their positions. |
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Term
| What are the five different types of galaxies found in the universe? |
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Definition
Spiral Galaxies
Elliptical Galaxies
Irregular Galaxies
Low Surfess Brightness Galaxies
Dwarf Galaxies |
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Term
| Which galaxy type has the most gas, dust? |
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Definition
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Term
| Which galaxy type has the least gas, dust? |
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Definition
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Term
| Which galaxy type has the oldest stars? |
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Definition
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Term
| Which galaxy types has the youngest stars? |
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Definition
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Term
| Which galaxy type are typically the largest galaxies in the universe? |
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Definition
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Term
| Which galaxy type are typically the smallest galaxies in the universe? |
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Definition
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Term
| What causes the different galaxy types? |
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Definition
| Merger - the resultant galaxy from when galaxies collide and form a single larger system. |
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Term
| Where is the Sun located in the Milky Way? (How do we know?) |
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Definition
| The Sun is 28,000 ligh-years out from the galactic center. We know this by measuring the distances to the globular clusters. |
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Term
E = m c squared
What does it mean? Why is it important? |
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Definition
Energy = mass X speed of light squared
This relationship states that mass and energy are EQUIVALENT and that mass can become energy.
A small amount of mass contains a LARGE amount of energy. |
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Term
| Where do stars form in our galaxy? |
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Definition
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Term
| How does graviational contraction work? |
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Definition
| Outward gas pressure (temperature) is less than the inward gravity (mass of cloud) |
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Term
| From protostars to main sequence stars (what are the steps involved)? |
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Definition
- The protostar "moves" down and to the left on the H-R diagram towards the Main Sequence. (The protostar has a "surface" now).
- High luminosity comes from gravitational collapse, surface temperature remains constant as the protostar shrinks.
- Slow steady contraction until equilibrium is reached.
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Term
| What is the process of the Proton-proton cycle? |
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Definition
Nucleus of hydrogen ---> He(nucleus of Helium) + 2y(Gamma Ray photons-ray of light)
=
Helium + light
Two protons fuse to form the isotope of hydrogen. |
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Term
| What are the energy sources of the stars? (What do we know it CAN'T be?) |
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Definition
Fusion is the process where two hydrogen atoms combine to form a helium atom, releasing energy.
It cannot be coal or wood. |
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Term
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Definition
The higher the mass of a star, the hotter and more luminous it is.
- High-mass stars require more pressure to support their greater mass.
- Greater pressure is produced by higher temperature
- Higher temperature produces higher luminosity
- Higher luminosity leads to faster fuel usage
- Faster fuel usage means a high-mass star burns out soon than a low-mass star.
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Term
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Definition
For low mass stars, the temperature never gets hot enough in the core to begin helium fusion.
For intermediate mass stars, the core eventually becomes hot enough for helium fusion to begin in the core and the star grows to become a RED GIANT. Because the envelope is very distended, rapid mass loss occurs in red giants. |
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Term
| Red giants/red supergiants (what are they? why do they form?) |
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Definition
Red giant: a cool, luminous star with a radius much larger than the Sun's. Red giants are found in the upper right portion of the H-R diagram.
Red Super Giants: a very large-diameter and luminous star, typically at least 10,000 times the Sun's luminosity.
When a star is a red giant or supergiant, it possesses a strong stellar wind. The winds strip away most of a giant's mass and the gravitation force squeezing the core drops. |
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Term
| Planetary nebulae (what are they? how do they form?) |
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Definition
a planetary nebula is a shell of gas ejected by a low-mass star late in its evolutionary lifetime. Plaentary nebulae typically appear as a glowing gas ring around a center star.
They form when the envelope of a red giant expands. The nebula eventually expands and dissipates leaving behind a dense stellar core that is inactive. IT IS REMNANT OF WHAT USED TO BE A STAR.
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Term
| White dwarf stars (what are they?) |
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Definition
a white dwarf star is a dense star whose radius is approximately the same as the Earth's but whose mass is comparable to the Sun's. White dwarfs burn no nuclear fuel and shine by residual heat. They are the end stage of stellar evolution for low-mass stars like the Sun.
- Composed of mostly carbon nuclei
- Temp up to 50,000 degrees k
- No internal energy source
- radius = about Earth-sized
- Mass equals that of the remnant core
- VERY DENSE!
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Term
| Supernovae (what are they? why do they occur?) |
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Definition
| A supernova is an explosion marking the end of most massive stars' evoluton. The explosion is triggered when mass from a companion star falls onto the white dwarf and causing the star to collapse. Type II supernovae probably occur when a massive star's iron core collapses. |
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