Astronomy

0% Complete
0 out of 65 Lessons
0% Complete
0 out of 4 Exams
Previous Lessons
Open Chapter Ch. 1: A Modern View of the Universe
Lesson #1 The Scale of the Universe
Incomplete Assignment Study Questions for Lesson 1
Lesson #2 The History of the Universe
Incomplete Assignment Study Questions for Lesson 2
Lesson #3 Spaceship Earth
Incomplete Assignment Study Questions for Lesson 3
Open Chapter Ch. 2: Discovering the Universe for Yourself
Lesson #4 Patterns in the Night Sky
Incomplete Assignment Study Questions for Lesson 4
Lesson #5 The Reason for Seasons
Incomplete Assignment Study Questions for Lesson 5
Lesson #6 The Moon, our Constant Companion
Incomplete Assignment Study Questions for Lesson 6
Lesson #7 Ancient Mystery of the Planets
Incomplete Assignment Study Questions for Lesson 7
Open Chapter Ch. 3: The Science of Astronomy
Lesson #8 The Ancient Roots of Science
Incomplete Assignment Study Questions for Lesson 8
Lesson #9 Ancient Greek Science
Incomplete Assignment Study Questions for Lesson 9
Lesson #10 The Copernican Revolution
Incomplete Assignment Study Questions for Lesson 10
Lesson #11 The Nature of Science
Incomplete Assignment Study Questions for Lesson 11
Open Chapter Ch. 4: Understanding Motion, Energy, and Gravity
Lesson #12 Describing Motion
Incomplete Assignment Study Questions for Lesson 12
Lesson #13 Newton's Laws of Motion
Incomplete Assignment Study Questions for Lesson 13
Lesson #14 Conservation Laws in Astronomy
Incomplete Assignment Study Questions for Lesson 14
Lesson #15 The Force of Gravity
Incomplete Assignment Study Questions for Lesson 15
Open Chapter Ch. 5: Light: The Cosmic Messenger
Lesson #16 Basic Properties of Light and Matter
Incomplete Assignment Study Questions for Lesson 16
Lesson #17 Learning from Light
Incomplete Assignment Study Questions for Lesson 17
Lesson #18 Collecting Light with Telescopes
Incomplete Assignment Study Questions for Lesson 18
Exam Exam 1
Open Chapter Ch. 6: Formation of the Solar System
Lesson #19 A Brief Tour of the Solar System
Incomplete Assignment Study Questions for Lesson 19
Lesson #20 The Nebular Theory of Solar System Formation
Incomplete Assignment Study Questions for Lesson 20
Lesson #21 Explaining the Major Features of the Solar System
Incomplete Assignment Study Questions for Lesson 21
Lesson #22 The Age of the Solar System
Incomplete Assignment Study Questions for Lesson 22
Open Chapter Ch. 7: Earth and the Terrestrial Worlds
Lesson #23 Earth as a Planet
Incomplete Assignment Study Questions for Lesson 23
Lesson #24 The Moon and Mercury: Geologically Dead
Incomplete Assignment Study Questions for Lesson 24
Lesson #25 Mars, a Victim of Planetary Freeze Drying
Incomplete Assignment Study Questions for Lesson 25
Lesson #26 Venus, a Hothouse World
Incomplete Assignment Study Questions for Lesson 26
Lesson #27 Earth as a living planet
Incomplete Assignment Study Questions for Lesson 27
Open Chapter Ch. 8: Jovian Planet Systems
Lesson #28 A Different Kind of Planet
Incomplete Assignment Study Questions for Lesson 28
Lesson #29 A Wealth of Worlds: Satellites of Ice and Rock
Incomplete Assignment Study Questions for Lesson 29
Open Chapter Ch. 9: Asteroids, Comets, and Dwarf Planets
Lesson #30 Classifying Small Bodies
Incomplete Assignment Study Questions for Lesson 30
Lesson #31 Asteroids
Incomplete Assignment Study Questions for Lesson 31
Lesson #32 Comets
Incomplete Assignment Study Questions for Lesson 32
Lesson #33 Pluto and the Kuiper Belt
Incomplete Assignment Study Questions for Lesson 33
Lesson #34 Cosmic Collisions - Small Bodies vs Planets
Incomplete Assignment Study Questions for Lesson 34
Open Chapter Ch. 10: Other Planetary Systems
Lesson #35 Detecting Planets Around Other Stars
Incomplete Assignment Study Questions for Lesson 35
Lesson #36 The Nature of Planets Around Other Stars
Incomplete Assignment Study Questions for Lesson 36
Lesson #37 The Formation of Other Planetary Systems
Incomplete Assignment Study Questions for Lesson 37
Exam Midterm Exam
Open Chapter Ch. 11: Our Star
Lesson #38 The Sun, Our Star
Incomplete Assignment Study Questions for Lesson 38
Lesson #39 Nuclear Fusion in the Sun
Incomplete Assignment Study Questions for Lesson 39
Lesson #40 Sun-Earth Connection
Incomplete Assignment Study Questions for Lesson 40
Open Chapter Ch. 12: Surveying the Stars
Lesson #41 Properties of Stars
Incomplete Assignment Study Questions for Lesson 41
Lesson #42 Patterns in the Stars
Incomplete Assignment Study Questions for Lesson 42
Lesson #43 Star Clusters
Incomplete Assignment Study Questions for Lesson 43
Open Chapter Ch. 13: Star Stuff
Lesson #44 Star Birth
Incomplete Assignment Study Questions for Lesson 44
Lesson #45 Life as a Low Mass Star
Incomplete Assignment Study Questions for Lesson 45
Lesson #46 Life as a High Mass Star
Incomplete Assignment Study Questions for Lesson 46
Open Chapter Ch. 14: The Bizarre Stellar Graveyard
Lesson #47 White Dwarfs
Incomplete Assignment Study Questions for Lesson 47
Lesson #48 Neutron Stars
Incomplete Assignment Study Questions for Lesson 48
Lesson #49 Black Holes: Gravity’s Ultimate Victory
Incomplete Assignment Study Questions for Lesson 49
Exam Exam 3
Open Chapter Ch. 15: Our Galaxy
Lesson #50 The Milky Way Revealed
Incomplete Assignment Study Questions for Lesson 50
Lesson #51 Galactic Recycling
Incomplete Assignment Study Questions for Lesson 51
Lesson #52 The History of the Milky Way
Incomplete Assignment Study Questions for Lesson 52
Open Chapter Ch. 16: A Universe of Galaxies
Lesson #53 Islands of Stars
Incomplete Assignment Study Questions for Lesson 53
Lesson #54 Distances of Galaxies
Incomplete Assignment Study Questions for Lesson 54
Lesson #55 Galaxy Evolution
Incomplete Assignment Study Questions for Lesson 55
Lesson #56 The Role of Supermassive Black Holes
Incomplete Assignment Study Questions for Lesson 56
Open Chapter Ch. 17: The Birth of the Universe
Lesson #57 The Big Bang Theory
Incomplete Assignment Study Questions for Lesson 57
Lesson #58 Evidence for the Big Bang
Incomplete Assignment Study Questions for Lesson 58
Lesson #59 The Big Bang and Inflation
Incomplete Assignment Study Questions for Lesson 59
Open Chapter Ch. 18: Dark Matter, Dark Energy, and the Fate of the Universe
Lesson #60 Unseen Influences in the Cosmos
Incomplete Assignment Study Questions for Lesson 60
Lesson #61 Structure Formation
Incomplete Assignment Study Questions for Lesson 61
Open Chapter Ch. 19: Life in the Universe
Lesson #62 Life on Earth
Incomplete Assignment Study Questions for Lesson 62
Lesson #63 Life in the Solar System
Incomplete Assignment Study Questions for Lesson 63
Lesson #64 The Search for Extraterrestrial Intelligence
Incomplete Assignment Study Questions for Lesson 64
Lesson #65 Interstellar Travel and Implications for Civilizations
Incomplete Assignment Study Questions for Lesson 65
Exam Final Exam

Assignments:

Unfinished Assignment Study Questions for Lesson 16

Lesson Objectives:

- What is light
- Light as a wave
- Light as a particle
- Forms of light
- Understanding matter and atoms
- Interaction between light and matter



Prior to Newton's experiments with light in the 1660s, it was already known that passing white light through a prism created a rainbow of color called a spectrum. The visible light seen in a spectrum, however, is only a tiny part of the complete spectrum of light, which is usually called the electromagnetic spectrum. The image in the figure shows the electromagnetic spectrum, which is the complete spectrum of light. Another name for light is electromagnetic radiation.



Light is a wave, which means it transmits energy without carrying material along with it. A wave moves up through peaks, and down through troughs.

Wavelength is the distance between adjacent peaks. Frequency is the number of times the wave moves up and down each second. It is measured in hertz, or the number of cycles per second.

Wavelengths increase as we go from gamma rays to radio waves, while frequency and energy are the opposite. The longer the wavelength, the lower the frequency, and vice-versa.

Light can interact with both electrically charged particles and magnetic fields, meaning it is an electromagnetic wave. That is why it is called electromagnetic radiation and the full spectrum of light is called the electromagnetic spectrum.



Light can behave both as a wave and as a particle. Particles of light are called "photons," and are characterized by a wavelength and frequency. The higher the frequency of the photon, the more energy the light carries.

All light travels at the same speed, which is about 300,000 kilometers per second. So a radio wave moves just as quickly as visible light, which moves at the same speed as a gamma ray. The difference in light is based on the frequency and wavelength - the speed stays the same.



There are many forms of light - radio waves, infrared, ultraviolet, x-rays, microwaves, and gamma rays, with radio waves being on the left end of the electromagnetic spectrum and having the longest wavelength, to gamma rays on the right extreme with the shortest wavelength.

Visible light has a wavelength of 400 nanometers, or 400 billionths of a meter, at the blue or violet end of the spectrum and 700 nanometers at the red end. If the light has a wavelength a bit longer than red light, then it is infrared. If it has a wavelength a little shorter than blue or violet light, then it is ultraviolet.

Around the border between infrared and radio waves is often called microwaves, since the wavelengths range from micrometers to centimeters.

The light our eyes can see is inside of an extremely limited segment of the electromagnetic spectrum. The reddest light we can see has a wavelength only twice as long as the bluest blue, while the radio waves from a radio station are a billion times longer than the X rays used in a doctor's office.



Ancient Greeks believed all matter came from fire, water, earth and air. Some Greeks starting with Democritus believed that these four elements were made up of tiny particles called atoms, which comes from a Greek word meaning indivisible.

Over time, we have learned that there are actually more than 100 chemical elements, each composed of a different type of atom, and that atoms themselves are made up of particles called protons, neutrons, and electrons.

Electrical charge is the physical property that describes how an object will interact with electromagnetic fields. Protons have a positive electrical charge (written as "plus 1") and electrons have a negative charge (minus 1). Neutrons are neutral with no charge.

At the center of the atom is the nucleus, which is made up of the protons and neutrons. The electrons surround the nucleus. The atom is held together because oppositely charged particles attract, so the negatively charged electrons are attracted to the positive charge of the protons inside of the nucleus.



What makes each element unique is the number of protons in each of its atoms. The number of protons in an element is called its atomic number. For example, Carbon always has six protons, so its atomic number is six.

When you combine the number of neutrons and protons in the nucleus of an atom, you get that element's atomic mass number. Carbon usually has an atomic mass number of twelve, since a typical atom has six protons and six neutrons, but the number of neutrons can vary. Isotopes are versions of an element with a different number of neutrons, so the most common isotope of carbon is carbon-12, with six protons and six neutrons, but there are also carbon-13 and carbon-14, with seven and eight neutrons, respectively.

Although there are only 118 chemical elements that have been identified so far, the number of material substances that exist is far greater because atoms from different elements combine to form molecules. For example, water exists because two hydrogen atoms bond with one oxygen atom.



For the study of astronomy, understanding how light and matter interact is very important. Light and matter interact in four ways.

The first way is emission. Matter can emit light; for example, we see a light bulb emit visible light.

Matter can absorb light. An example of this is when you place your hand near a light bulb. Your hand absorbs some of the light and this absorbed energy warms your hand.

Some forms of matter transmit light, or allow it to pass through. Examples are glass and air.

Finally, matter can reflect or scatter light when it causes light to bounce off. If the light bounces all in the same general direction, it is called reflection, and when it bounces off more randomly, we say that it scatters.

When a material transmits light, it looks transparent, whereas when it absorbs light, it is opaque. Many materials are partially transparent or partially opaque.

The color of an object is based on what light it transmits or reflects. For example, a leaf reflects green light but absorbs all other colors.