Other
Bad Astronomy/phil Plait: Tides and Why Our Days Are Getting Longer
Why does the Moon always shows the same face to the Earth? Why is the Moon's rotation period the same as the length of time it takes to orbit the Earth? Why are there two tides a day? These questions and more are answered here.
PBS
Pbs Learning Media: More on Galileo's Big Mistake
Even great scientists make mistakes! This illustrated essay from the NOVA Web site looks at Galileo's theory of the tides, which, while well thought out, was wrong.
Enchanted Learning
Enchanted Learning: Earth's Oceans Tides
This site explains what tides are and the difference between Proxigean Spring Tides, spring tides, and neap tides, and how these are formed. Graphic illustrations are provided.
Curated OER
Eyes on the Sky, Feet on the Ground: The Earth's Moon
In this online textbook produced by the Smithsonian, students explore the phases of the moon, the moon's orbit, the origin of the moon, and the tides. Includes numerous inquiry-based activities.