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Astronomy Notes
LESSON 1
Solar System
axis of rotation
period of rotation
period of revolution
ellipse
astronomical unit
11.1 Structure of the Solar System
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
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
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
The Motion of the Planets (cont.)
11.1 Structure of the Solar System
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.
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
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
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
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
The Astronomical Unit (cont.)
11.1 Structure of the Solar System
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
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
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
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
Lesson 2
Stars
What are stars?
• Stars are balls of plasma, mostly hydrogen, that produce light by nuclear reactions in their cores.
12.1 Stars
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
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
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
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?
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
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
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
The H-R Diagram
12.1 Stars
Lesson 3
Galaxies
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
Types of Galaxies
• Galaxies have different sizes and shapes.
• Spiral galaxies can be regular or barred.
12.3 Galaxies
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
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
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
The Milky Way
• Our solar system is located in the Milky Way galaxy.
12.3 Galaxies
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
The Distances Between Galaxies
• Galaxies are so far away that even the closest galaxies appear as fuzzy patches of light.
12.3 Galaxies
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
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
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
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
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
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
The Formation of Galaxies (cont.)
• The dense regions began to clump and form stars.
12.3 Galaxies
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
