Principles of Astronomy

This work was created by Dr Jamie Love

and

licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

In this online sample, only the first quarter of the course is available. The other lessons are included in the complete hypertextbook. To learn more about this course and hypertextbook, visit the Principles of Astronomy website.

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Frequently Asked Questions

Principles of Astronomy
created by Dr Jamie Love 1997 - 2018

Welcome to your astronomy lessons.

Universal Time

January February March First Quarter Exams
April May June Second Quarter Exams
July August September Third Quarter Exams
October November December Fourth Quarter Exams

To keep up with current observations, reinforce specific lessons and complement your learning experience, be sure to spend some time looking at
the night sky and plan your observations for .

Here's your support materials - the Study Guide, the List of Terms learned and the List of Objects seen.

January

Introduction to the Course (Check the study guide for this lesson)
Please start here to learn what the course is all about and how to get the most out of it. This lesson will also address some of the most frequently asked questions.
Getting Your Bearings (Check the study guide for this lesson)
You'll learn how to find the "North Star" and use it to figure out which way is north, your latitude and how much time has passed. You'll also learn how we keep track of the nightly motion of the stars by using "right ascension" and you will learn the terms needed to explain the location of an object as seen by an observer. The Dippers, plus URSA MAJOR, URSA MINOR, and CASSIOPEIA are introduced.
The Earth's Motion (Check the study guide for this lesson)
The Earth's motion causes the sky to appear to move and understanding this motion is very important for understanding observational astronomy. Here you'll learn how the Earth moves, how to imagine the sky "motion" and how to keep track of it.
Optical Devices (Check the study guide for this lesson)
You do NOT need a telescope in order to enjoy astronomy. However, all amateur astronomers should understand how a telescope works. In this lesson I will teach you about the wonderful area of physics known as "optics" and show you how astronomers bend light in order to better view the universe.

February

Star Names and Brightness (Check the study guide for this lesson)
Each star can have several names and here I'll explain the modern system of naming stars based upon their brightness. This leads us to a short lesson on distances in space. I'll also explain declination - the sky equivalent to the Earth's latitudes. This will further your understanding of celestial coordinates and show you a different way to think about circumpolar stars. ORION and his two dogs, CANIS MAJOR and CANIS MINOR, are featured in this month's lesson.
The Moon's Motion (Check the study guide for this lesson)
The Moon's apparent motion explains our tides and tides explain why the Moon shows only one face to us. In this lesson I'll teach you how the Moon orbits the Earth. The physics you will learn in this lesson is relevant not only to the Moon but to all orbiting objects.
The Phases of the Moon (Check the study guide for this lesson)
You'll learn how the relative positions of the Earth, Moon and Sun cause the phases of the Moon. You'll also be introduced to two very important terms - synodic period and sidereal period. This lesson will lay down a solid foundation for later discussion about eclipses, orbits and the motion of planets.
The Lunar Landscape (Check the study guide for this lesson)
No one can look at the Moon without asking, "What is that part of the Moon called?". Even with the naked eye the Moon has obvious features and a small pair of binoculars will bring out lots of detail. In this lesson I will give you a tour of the Moon, pointing out its most obvious features and explaining how to get the best views. I'll even throw in a wee bit of lunar geography.

March

Star Colors and Temperatures (Check the study guide for this lesson)
You may have noticed that stars come in several colors. In this lesson you'll learn what causes differences in color as I introduce you to the physics of a star's surface. I'll also teach you how to find the constellation of TAURUS, the Bull.
Color Designation and the Hertzsprung-Russell Diagram (Check the study guide for this lesson)
This lesson builds upon the previous one by teaching you how we classify stars by color. We then use what you have just learned to introduce an important chart in astronomy - the Hertzsprung-Russell diagram. Along the way I will teach you the stars of The Twins (GEMINI) and the Charioteer (AURIGA). At the end of this lesson I will provide you with a map upon which you can test your identification skills and from which you can study.
The Positions of the Planets (Check the study guide for this lesson)
The planets are constantly changing their positions against the starfield and this can confuse students. Astronomers have developed a series of terms to describe the most important positions of the planets and in this lesson you will learn them all.
The Motion of the Planets (Check the study guide for this lesson)
Now that you know how we name the planets' positions you are ready to tackle how planets move. After this lesson you will have an understanding of some of the most important concepts in observational astronomy.

April

The Birth of Stars (Check the study guide for this lesson)
Here you will learn how a star is born and ends up on the H-R diagram. I'll show you how to find our nearest "star nursery" and teach you a trick (called "averted vision") that helps you see dim objects.
Star Clusters (Check the study guide for this lesson)
Stars are born in "families" called clusters. I'll teach you how clusters age and show you how to find several types of clusters in various stages of aging. In the process I'll show you how to identify two new Zodiac constellations - CANCER, the Crab and LEO, the Lion. I'll also show you some less well-known constellations - HYDRA, the Water Snake, SEXTANS, the Sextant, CRATER, the Cup, and CORVUS, the Crow.
Star Physics (Check the study guide for this lesson)
In this lesson I will teach you how a star creates its power by fusing atoms together. I'll also introduce you to the Eddington limit, a simple relationship that tells you how bright a star can really be. Some students may find this lesson difficult and be frightened by the equations but you don't need to understand all these details. I'm just presenting it because it is of interest to many folks and is NOT beyond the ability of most people to understand. Please give it a try. You may be a budding astrophysicist and not even know it!
Star Structure and Spectroscopy (Check the study guide for this lesson)
Stars are not simply balls of gas. They have a structure that defines how they work and affects their surface appearance. In this lesson I will show you the anatomy of a star, using the Sun as an example. Then I'll teach you about one of the most important techniques in astronomy since the invention of the telescope - spectroscopy! We will return to the subject of spectroscopy throughout the remainder of this course so this is a particularly important topic to understand.

May

Aging Stars and Red Giants (Check the study guide for this lesson)
The population of stars in our neighborhood is like the population of people in your neighborhood. They are born at different times so they have different ages. But stars age at different rates, based upon the star's mass, and when they enter old age they go through an amazing transformation to become red giants. In this lesson I'll teach you how a star's physics and structure change as it ages and how red giants come about.
Planetary Nebula and White Dwarfs (Check the study guide for this lesson)
All stars eventually die. After "old age", as a red giant, our Sun (like most stars) will explode, throwing much of its material into space and leaving behind a very curious "corpse". Learn all about it!
Spring Stars and Constellations (Check the study guide for this lesson)
In this lesson I will teach you how to identify many stars and constellations that appear in the sky during the spring months - BÖÖTES (The Herdsman), VIRGO (The Virgin), LYRA (The Harp), CORONA BOREALIS (The Northern Crown) and HERCULES. Along the way I will point out some objects that relate to the previous lessons.
The Earth's Aurora (Check the study guide for this lesson)
Here I will teach you about the beautiful, spooky and "mysterious" lights that visit our night sky. (No, no - not flying saucers! ) The auroras are caused by a combination of the Sun's solar winds and the Earth's magnetic field. In this lesson you will learn about this important area of astrophysics. This will extend your knowledge about the Sun and our own world.

June

Supernovas and Neutron Stars (Check the study guide for this lesson)
Here you will learn how a supergiant ages and dies in a huge explosion - a supernova. The "corpse" left behind is not a white dwarf but a strange thing called a neutron star.
Pulsars (Check the study guide for this lesson)
Most neutron stars spin very rapidly and as they do they beam large amounts of energy in a pulsating manner. I'll teach you about these incredible "astro tickers". Then I'll show you where you can find a pulsar and remnants of a supernova - the Crab Nebula. (You need a telescope to see it but it's worth knowing where it hides.)
Black Holes (Check the study guide for this lesson)
Extremely big supergiants don't go out with a bang - they just go out! This lesson completes your education about stellar aging by introducing you to the most incredible object in the universe - a black hole. I'll even tell you the location of a particularly close black hole and in the process I'll teach you how to identify the most familiar landmark (skymark?) in the summer night sky - the Great Summer Triangle - which includes LYRA, the Harp (which you know from last month), plus CYGNUS (the Swan) and AQUILA (the Eagle).
Orbits (Check the study guide for this lesson)
We've talked a lot about orbits but so far I have been keeping it simple and leaving some gaps in your education. In this lesson I will correct that as I teach you about the more complicated side of orbits, such as inclinations and Kepler's three laws of planetary motion. Every astronomer, from amateurs to professionals, understands these important complications because they help to explain more advanced subjects like multiple star systems, occulations and eclipses.

July

Eclipses (Part 1) (Check the study guide for this lesson)
Eclipses are a very important part of astronomy. To understand them you have to learn the fundamentals of the geometry of orbits and the physics of shadows. That's what this lesson will teach you.
Eclipses (Part 2) (Check the study guide for this lesson)
Here you will learn about some of the incredible phenomena that can be seen during an eclipse. I will tell you what I saw during two complete solar eclipses that I've witnessed! We'll conclude this lesson by talking you through the path of an eclipse.
Multiple Star Systems (Check the study guide for this lesson)
You may be surprised to learn that single star systems, like our own Solar System, are in the minority. Most stars have a companion or two. Here I will teach you how they formed, how they work and how to find a particular binary star that is eclipsed by its partner. In the process, I'll teach you a new constellation - PERSEUS.
Multiple Star Systems and Novas (Check the study guide for this lesson)
Some multiple star systems have properties that cause them to explode! Here you will learn about simple recurrent novas and Type I supernovas. I'll show you where to find some multiple star systems, show you where some nova have been seen, and along the way you'll learn some more stars and constellations.

August

The Formation of our Solar System and Long Period Comets (Check the study guide for this lesson)
Building upon what you learned in June about orbits, we now move into the advanced stuff! First I will tell you how our Solar System formed and this will help you to better understand the behavior of planets. Then I'll explain how some of the leftover bits ended up as comets that hide in the farthest reaches of the Solar System.
Short Period Comets and Comets in General (Check the study guide for this lesson)
Here you will learn about the more common and predictable short period comets including where they come from. I'll also teach you much more about comets, such as their composition, shape and behavior.
Meteors and Asteroids (Check the study guide for this lesson)
I think meteors and asteroids are fantastic and in this lesson I will tell you where they hang out and when is the best time to see meteor showers. I will teach you a little bit about their composition and how they are classified. We will conclude this lesson with a little story about interplanetary travel (of rocks).
The Late Summer Night Sky (Check the study guide for this lesson)
OK, now that you know all about meteors, I'll teach you how to spot the best meteor shower of the year! In the process, I'll introduce you to several more constellations (PEGASUS, LIBRA, SCORPIUS, SAGITTARIUS, OPHIUCHUS, and the two SERPENS) and stars.

September

The Tilt of a Planet's Rotation (Check the study guide for this lesson)
You may be surprised to learn that all the planets rotate at an angle to the path of their orbits. They have a tilt! I'll show you how the Earth's tilt causes our seasons and affects how we view the night sky. I'll also tell you how other planets are tilted.
The Path of the Sun in our Sky (Check the study guide for this lesson)
The tilt of the Earth causes the path of the Sun to change as the year goes by. Here I will show you how that affects our day/night times, and how we can use that information to help plan our viewing of planets.
The Milky Way Galaxy (Check the study guide for this lesson)
This lesson will introduce you to the galaxy in which we live. It's huge! Here you will learn about the shape, complexity and motion of our galaxy. I will also tell you how you can view our Milky Way Galaxy.
The Local Group (of Galaxies) (Check the study guide for this lesson)
Our galaxy is big but our neighborhood is bigger. In this lesson I will show you how to see, with your naked eye, our nearest neighboring galaxy - the Andromeda Galaxy. I'll also show you where you can find a few other nearby galaxies (with magnification) and a new, tiny constellation.

October

Classification of Galaxies (Check the study guide for this lesson)
Galaxies come in a wide variety of sizes and shapes so keeping track of them might seem overwhelming. Here I will teach you about a simple and useful method, developed by Hubble, for classifying galaxies. I will also introduce you to another "luminary" in astronomy - Charles Messier - and explain how his system of naming "fuzzy objects" are regularly used by amateur astronomers.
Structure, Evolution and Dynamics of Galaxies (Check the study guide for this lesson)
We begin this lesson by first returning to the idea of Population I and II stars and I will put them in perspective for you. Then we will go into more detail about galaxies as I teach you (our current understanding of) how galaxies age and how they interact.
The Zodiac (Check the study guide for this lesson)
I'm sure you've heard of the Zodiac and you have already learned some of its constellations. In this lesson I will tell you why the Zodiac is important and how astronomers use it. Also, I will show you how to find the remaining Zodiac constellations (CAPRICORNUS, AQUARIUS, PISCES and ARIES).
Celestial Coordinates (Check the study guide for this lesson)
OK, OK, I know that we have covered this subject before... But have we? Now that you understand the Zodiac you are ready to learn about the "First Point" and how it determines the RAs. In this lesson I will focus your mind on the important concepts that are the foundation of our celestial coordinate system and, in the process, review some important points. I will also show you two new, small and easily overlooked constellations - DELPHIUS, the Dolphin, and SAGITTA, the Arrow.

November

Strange Galaxies (Check the study guide for this lesson)
So far, you have learned about ordinary galaxies but there are some very strange galaxies out there. Most are very far away and produce huge amounts of energy. In this lesson I will tell you about those strange galaxies, what causes them to produce so much energy and what we can learn from them.
Precession of the Earth (Check the study guide for this lesson)
As if the world weren't complicated enough, now we come to precession! This important concept will not affect your astronomical observations but every astronomy student should understand how this slow wobble of the Earth will cause Polaris to move away from the Celestial North. During this lesson you will also learn some more constellations (CEPHEUS, the King and DRACO, the Dragon) and a little bit of Ancient history too
Distances in Space (Check the study guide for this lesson)
We have covered a lot of distance in this course - billions of light-years! In this lesson you will learn how astronomers go about estimating the distances to stars and galaxies. Don't let the math scare you. (Just read it and ignore it!) I will also tell you about another type of variable star and how to find it.
Movement in Space (Check the study guide for this lesson)
Everything is moving - even the stars but we don't notice it. In this lesson I will teach you how astronomers measure star motion and even use that motion to calculate the orbits of planets that orbit them! These techniques are also used to measure the motion of galaxies and it's important that you understand these techniques in order to appreciate the next month's lessons.

December

The Winter Southern Sky (Check the study guide for this lesson)
In this lesson I will teach you the remaining stars and constellations that can be seen from the Northern Hemisphere - PISCIS AUSTRALIS, Southern Fish, GRUS, the Crane, CETUS, the Sea Monster, ERIDANUS, the (wandering) River, LEPUS, the Hare and a few others . Some of these are so low on the southern horizon that you might not be able to see them all. That's a good introduction to our next lesson! Along the way I'll introduce you to Mira - a variable star that is a real treat for amateur astronomers.
The Extreme Southern Celestial Hemisphere (Check the study guide for this lesson)
In this lesson we take the big plunge south and show you some sights you cannot see from North America or Europe. However, you should be aware of some of these most important sights because the "wonder down under" includes our nearest neighbor (Alpha Centauri), nearest galaxies (Magellanic Clouds) and many other interesting objects. It would be wrong NOT to give you a small tour of these things. Learn where to find ARGO NAVIS, the Argo Ship, CARINA, the Keel, VELA, the Sails, PUPPIS, the Deck, MALUS, the Mast, PYXIS, the Compass, ANTLIA, the Pump, PICTOR, the Painter, CRUX AUSTRALIS, the Southern Cross, CENTAURUS, the Centaur, and many others!
The Expanding Universe (Check the study guide for this lesson)
All the galaxies outside our Local Group are moving away from us! That might seem odd but it's true and an important clue to the topic of our last lesson, so be sure you understand this one before going further. In this lesson I will teach you about Hubble's constant and return to the subject of quasars.
Cosmology (Check the study guide for this lesson)
Modern day astronomy allows us to collect data and analyze it in such a way as to give us a pretty good idea of where the universe came from and where it is going. This exciting field is sure to excite you and leave you feeling that there is more to your hobby than just staring at stars! What a great way to end our course!

Wishing you "Clear Skies",
Dr Jamie Love

This work was created by Dr Jamie Love and licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

Homepage How to get a FREE copy of the entire course (hypertextbook) Frequently Asked Questions

January	February	March	First Quarter Exams
April	May	June	Second Quarter Exams
July	August	September	Third Quarter Exams
October	November	December	Fourth Quarter Exams