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Basics of Celestial Motion
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Welcome to the Basics of Celestial Motion. This website is designed to introduce the “science-shy”, the “celestially misinformed” and anyone who doesn't know how much they really don't know about the Earth, Sun and Moon, to the facts about "celestial motion" or how these "celestial bodies" move in space relative to each other.

“Well what’s there to know?” you might ask. The Earth moves around the Sun in a year, the Moon moves around the Earth in a month, and the Earth spins on its own axis in a day. These are really basic facts that we all know and understand.

But do we really understand celestial motion?

Popular Astronomy Misconceptions

As basic as it all sounds many people, many smart people, really don't understand the motion of the Earth, Sun and Moon and how it affects how we experience our world. They believe they understand simple facts about celestial motion but instead they often subscribe to a number of very common or popular misconceptions. Take, for example, the following questions and answers about two basics of celestial motion:
  • Question #1: What causes the seasons?
    Answer: The seasons are caused by the Earth's changing distance from the Sun. When the Earth is closer to the Sun it grows warmer so we have summer. When the Earth is farther from the Sun it is less warm so we have winter.
  • Question #2: What causes the phases of the Moon?
    Answer: The phases of the Moon are caused by the Earth's shadow falling on the Moon, blocking out the Sun, and making part or all of the Moon appear very dark or invisible.
References: [Bailey, et. al., 2003, Prather,, 2004, Sadler 1992]

If you thought the answers were correct then this site is for you!

You are not alone ...

In a well-known video documentary, entitled "A Private Universe", filmed at a 1989 Harvard University graduation, 21 of 23 students, alumni and faculty gave the answers indicated to the two questions above. The video later shows ninth graders from a local high school, with little science education, giving the same answers.

And every one of them -- from distinguished Harvard faculty down to "science-shy" ninth-grader -- was wrong!

How to Use this Site

Each of the website sections linked below introduces one popular misconception about celestial motion and then provides, in (hopefully) simple terms, a scientifically accurate explanation. The first two sections, The Earth and the Sun, and The Earth and the Moon discuss, respectively, the two popular misconceptions described above regarding the four seasons and the phases of the Moon, while the third section, The Major Planets, discusses a third "convenient misconception" about the relative sizes and distances of the planets from Earth. In each case the phenomenology of celestial motion is described in text and images, and key terms are introduced and historical context is provided when important. The final page of each section summarizes the basics of celestial motion, and provides links to other online astronomy resources to help you broaden your understanding and appreciate your new found understanding!

The goal of this website is to serve as a "stepping stone" to understanding more complex facets of astronomy.
The Earth and the Sun The Earth and the Moon The Major Planets
The Four Seasons The Phases of the Moon Solar System
The Seasons Phases of the Moon Celestial Magnitudes
Animation courtesy of Best Animations

About this Site | References | Image Usage | Glossary | Site Map
Note: this website has been created as the final design project for the course "Internet and WWW for Educators" (SED EM 610 OL) as part of the requirements for the Graduate Certificate in Internet Technology (CIT) at the Boston University School of Education. This site has been constructed primarily as a demonstration of educational website design.
Last Updated: December 8, 2006
Basics of Celestial Motion. Copyright 2006   S. E. ScruggsEmail Address