Astronomy Notes - Weeblybouldercreekwinters.weebly.com/.../astronomy_notes_only.pdf–The missing...
Transcript of Astronomy Notes - Weeblybouldercreekwinters.weebly.com/.../astronomy_notes_only.pdf–The missing...
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Astronomy Notes
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LESSON 1
Solar System
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axis of rotation
period of rotation
period of revolution
ellipse
astronomical unit
11.1 Structure of the Solar System
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What is the solar system?
• Our solar system includes planets and dwarf planets, their moons, a star called the Sun, asteroids and comets.
11.1 Structure of the Solar System
• Planets, dwarf planets, asteroids, and comets all orbit the Sun.
Solar Systems
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The Motion of the Planets
• Planets spin like a top spins on the floor.
• This spin is known as rotation.
• The axis of rotation is an imaginary line through the center of the planet around which the planet rotates.
11.1 Structure of the Solar System
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The Motion of the Planets (cont.)
• Period of rotation—the amount of time it takes to make one complete rotation
• Period of revolution—the time it takes a planet to move around the Sun.
11.1 Structure of the Solar System
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The Motion of the Planets (cont.)
11.1 Structure of the Solar System
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Kepler’s Laws of Planetary Motion
• Kepler studied the motion of planets in the early 1600s.
11.1 Structure of the Solar System
• He proposed three laws that govern the motion of the planets.
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Kepler’s First Law: Planets Orbits the Sun in Elliptical Paths
• Kepler concluded that Mars’ orbit around the Sun is an oval, or ellipse.
11.1 Structure of the Solar System
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Kepler’s Second Law: Equal Area in Equal Time
• A line joining any planet to the Sun sweeps out equal areas in equal time.
• Planets move faster when they are closer to the Sun than when they are far from the Sun.
11.1 Structure of the Solar System
Block 2—4/13
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Kepler’s Third Law: Orbital Period Increases with Distance from the Sun
• A planet’s period of revolution increases as its distance from the Sun also increases.
11.1 Structure of the Solar System
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The Astronomical Unit
• The astronomical unit (AU) is the average distance between the Sun and Earth.
• One AU is about 1,496,000,000 km.
11.1 Structure of the Solar System
Block 1—4/13
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The Astronomical Unit (cont.)
11.1 Structure of the Solar System
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Gravity and the Solar System
• Recall that all objects that have mass attract each other.
• The planets are attracted towards the Sun.
11.1 Structure of the Solar System
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The Law of Universal Gravitation
• Isaac Newton explained that the force holding the planets in orbit was gravity.
11.1 Structure of the Solar System
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Formation of the Solar System
• Some scientist think that the solar system was formed from a giant cloud of gas and dust called a nebula.
• Dense areas in the cloud attracted more mass and became even more dense.
11.1 Structure of the Solar System
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Gravity Forming Stars and Planets
• The center of the nebula became more dense and the temperature increased.
• The Sun formed from nuclear reactions in the center of the nebula.
• Material farther away from the center of the nebula formed a disk and began to clump together, eventually becoming planets.
11.1 Structure of the Solar System
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Lesson 2
Stars
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What are stars?
• Stars are balls of plasma, mostly hydrogen, that produce light by nuclear reactions in their cores.
12.1 Stars
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The Structure of Stars
• Stars have layered structures.
• Energy is produced in the core.
• Temperatures range from 5,000,000K to 100,000,000K in the core.
• Atoms separate from their nuclei forming plasma.
12.1 Stars
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Types of Stars
• Stars have many sizes, masses, and surface temperatures.
• Our Sun is a medium-sized star with a surface temperature of about 5800K.
12.1 Stars
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Distances Between Stars
• One AU is the average distance between the Sun and Earth.
• A light-year is the distance light travels in one year—9,500,000,000,000 km or 63,000 AU.
12.1 Stars
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What are stars made of?
• Stars can only be studied by the light they emit.
• A spectroscope is an instrument that is used to study light.
• Astronomers can determine what elements are present in a star.
12.1 Stars
How does the chemical composition of stars determine their classification?
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The Brightness of Stars
• The brightness of stars depends on two things—energy (absolute Brightness) and distance. • Light looks brighter as you move closer to the source.
12.1 Stars
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Classifying Stars—The H-R Diagram
• Two astronomers independently developed diagrams of how absolute magnitude, or luminosity, is related to the temperature of stars.
12.1 Stars
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Classifying Stars—The H-R Diagram
• 90% of stars fall on a diagonal, curved line, called the main sequence.
• The remaining stars fall into one of three other groups.
(cont.)
– Red giants
– Supergiants
– White dwarfs
12.1 Stars
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The H-R Diagram
12.1 Stars
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Lesson 3
Galaxies
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Stars Cluster in Galaxies
• Stars are not uniformly distributed through the universe but gather in large groups called galaxies.
• Galaxies contain billions of stars.
• Star clusters within galaxies contain millions of stars.
12.3 Galaxies
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Types of Galaxies
• Galaxies have different sizes and shapes.
• Spiral galaxies can be regular or barred.
12.3 Galaxies
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Types of Galaxies (cont.)
• Both types have spiral arms when viewed from above.
• They have three components—the nucleus, arms, and halos.
12.3 Galaxies
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Types of Galaxies (cont.)
• The spiral arms are star-forming regions and the halo contains mostly old star clusters.
• From the side, spiral galaxies look flat.
12.3 Galaxies
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Types of Galaxies (cont.)
• Some galaxies contain a bar of stars, dust, and gas that passes through the center of the galaxy—these are called barred spirals.
12.3 Galaxies
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The Milky Way
• Our solar system is located in the Milky Way galaxy.
12.3 Galaxies
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Elliptical and Irregular Galaxies
• Elliptical galaxies have an oval shape and are composed of old, reddish stars.
• Irregular galaxies have a patchy appearance and are difficult to classify.
12.3 Galaxies
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The Distances Between Galaxies
• Galaxies are so far away that even the closest galaxies appear as fuzzy patches of light.
12.3 Galaxies
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The Local Group
• Galaxies are grouped together into clusters, which form superclusters.
• The Milky Way is part of a cluster called the Local Group.
12.3 Galaxies
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Superclusters
• Our cluster is part of the Virgo supercluster.
• The Virgo supercluster contains thousands of galaxies spread across 100 million light years.
• The farthest galaxies from Earth are about 14 billion light years away.
12.3 Galaxies
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The Big Bang Theory
• In the late 1920s, Edwin Hubble discovered that most of the galaxies he observed were moving away from Earth.
• This could only be explained if the entire universe as expanding.
• The Big Bang Theory states the expansion of the universe began about 14 billion years ago.
12.3 Galaxies
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The Big Bang Theory (cont.)
• The universe was a tiny point that contained all the energy and matter of the universe.
• The universe began to expand rapidly and cool.
12.3 Galaxies
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The Expanding Universe and the Big Bang Theory
• The universe was too hot to form elements for several hundred thousand years.
• The universe consisted of radiation and subatomic particles.
• As the universe cooled, hydrogen and helium atoms formed.
12.3 Galaxies
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The Formation of Galaxies
• Galaxies began forming several hundred million years after the Big Bang.
• Clouds of hydrogen and helium possibly became more dense in some regions.
12.3 Galaxies
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The Formation of Galaxies (cont.)
• The dense regions began to clump and form stars.
12.3 Galaxies
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Dark Matter and Dark Energy
• Scientists can calculate how much mass the universe should contain by the way galaxies move through space.
• All the matter they can detect added together is less than the amount needed.
– The missing matter is called dark matter.
– The missing energy needed to explain the expansion of the universe is called dark energy.
12.3 Galaxies