Chapter 8: Section 5 - The Sun-Earth-Moon System

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In this section you will find materials that support the implementation of EarthComm, Section 5: The Sun-Earth-Moon System.

Learning Outcomes

  • Use a model to explain the relative motions of Earth, the Moon, and the Sun.
  • Carry out an investigation that examines the changes in the appearance of the Moon in the night sky.
  • Analyze and interpret data to determine the relationship between the motion of the Moon and coastal tides.
  • Use mathematics to calculate how Earth’s rotation has changed over time due to tidal forces.
  • Obtain information about the formation of Earth and the Moon.

Using Technology

To learn more about tides, complete the following:

Tides and Lunar Phases

  1. Table 1 in the Student Edition shows data from the month of January 2009.  Obtain tidal data during the same period that you are doing your Moon observations. Select several cities nearest your community.
    1. Record the highest high tide and the lowest low tide data for each city. Choose at least eight different days to compare. Correlate these records to the appearance of the Moon during your observation period. Make a table like Table 1 showing high and low tides for each location.
    2.  What do you notice about the correlation between high and low tides and the appearance of the Moon?

To find tidal data for several different cities, visit the following web sites:

Tidal Current Predictions, NOAA

Tides and Currents Data, NOAA

IMPORTANT: Please review the following information to help understand the tidal prediction data. Or try the following pages on the NOAA - Center for Operational Oceanographic Products and Service:

What formats are tide predictions available in?
Standard Format - This format is available in hard copy and an electronic, ASCII file which provides time and height of tide information for a single location in a page readable format. The following example for EASTPORT, ME, April, 1997 shows the predictions in AM/PM Time and has been adjusted for Daylight Savings Time.

Eastport, Maine T.M. 75 W.
Tide Predictions (High and Low Waters) April, 1997
NOAA, National Ocean Service

Standard Time










1 Tu


H 18.6 


 L 0.7


H 17.8 


L  1.5

2  W 


H  18.8


L   0.4


H  18.2


3 Th


L   0.9


H 19.2


L  -0.2 


H  19.0

4  F


L   0.0 


H  20.0


L  -1.1


H  20.1

5 Sa


L  -1.2 


H  20.9


L  -1.9


H  21.1

Example for EASTPORT, ME, April-June, 1997.
Please Note: All heights are in feet.

How accurate are the predictions?
The accuracy of the tide predictions is different for each location. Periodically we do a comparison of the predicted tides vs the observed tides for a calendar year. The information generated is compiled in a Tide Prediction Accuracy Table. We work to insure that the predictions are as accurate as possible. However, we can only predict the astronomical tides, we cannot predict the effect that wind, rain, freshwater runoff, and other short-term meteorological events will have on the tides.

In general, predictions for stations along the outer coast are more accurate than those for stations farther inland; along a river, or in a bay or other estuary. Inland stations tend to have a stronger non-tidal influence; that is, they are more susceptible to the effects of wind and other meteorological effects than stations along the outer coast. An example of an inland station which is difficult to predict is Baltimore, Maryland. This station is located at the northern end of Chesapeake Bay. Winds which blow along the length of the bay have been known to cause water levels to be 1-2 feet above or below the predicted tides.

Stations in relatively shallow water, or with a small tidal range, are also highly susceptible to meteorological effects and thus difficult to accurately predict. At these stations, short-term weather events can completely mask the astronomical tides. Many of the stations along the western Gulf of Mexico fall into this category. An example is Galveston, Texas. This station is in a bay which is relatively shallow and has a small opening to the sea. At this station it is possible for meteorological events to delay or accelerate the arrival of the predicted tides by an hour or more.

Inquiring Further

  1. To learn more about why the Earth has two tidal bulges, visit the following web sites:

    Tides Online, NOAA
    Access current tide information.

    Ocean in Motion: Tides - Characteristics, Office of Naval Research
    Learn more about why the Earth has two tidal bulges instead of just one.
  2. To learn more about tidal forces throughout the solar system, visit the following web sites:

    Jupiter: Moons: Io, NASA
    Compare the tides on Io to Earth.

    Galileo Continues to Return Data from February's Flyby of Io, Jet Propulsion Laboratory
    In July 10 - 16, 2000, the Galileo spacecraft flew by Io and sent back new information about its tides.

    Saturn - Lord of the Rings, Tufts University
    Why do planets have rings? Find out about the connection between rings and tidal forces.
  3. To learn more about impact craters throughout the solar system, visit the following web sites:

    Finding Impact Craters, NASA
    Get more information about impact craters on Earth and the moon.

    Impact Craters on the Planets, Lunar and Planetary Institute
    Check out images of impact craters on Mercury, Venus, the Moon, Jupiter's moon, Ganymede, Saturn's moon, Dione, and Uranus' moon, Miranda.
  1. To learn more about Isaac Newton’s discoveries and inventions, visit the following web sites:

Isaac Newton's Discoveries and Inventions, Newton Online
Read about how Isaac Newton’s discoveries and inventions widened the reaches of human thought and demonstrated the power of the scientific way of thinking.


To learn more about this topic, visit the following web sites:

The Formation of the Earth and Moon

Age of the Earth, USGS
Find out more about what scientists believe how and when the Earth formed.

The Formation of the Earth's Moon, NASA
Learn about the restrictions theories for the formation of the moon must account for, why some theories work, and why some do not work.


Our Restless Tides, NOAA, CO-OPS
Explains the basic astronomical factors which produce tides and tidal currents.

High Tides and the Full Moon,  Cornell Astronomy
Learn about high tides and the lunar cycle.

Lunar Tides,  NASA
Look at how the Earth has a tidal effect on the Moon.

Animations and Video

To view animations and video related to this topic, visit the following web site:

Launchpad: Solar Eclipses, NASA
Locate and watch the NASA eClip titled, "Launchpad: Solar Eclipses."  This video examines the unique geometry of the Sun-Earth-Moon system that creates eclipses.

Launchpad: Newton's Laws On-Board the International Space Station, NASA
Locate and watch the NASA eClip titled, "Launchpad: Newton's Laws On-Board the International Space Station."  This video examines Newton's Laws of Motion and applies the laws to certain situations experienced by astronauts on the International Space Station.

Launchpad: Moon Magic, NASA
Locate and watch the NASA eClip titled, "Launchpad: Moon Magic."  This video examines the Moon’s orbit, including its effects on tides.