The primary source of the tides is the moon's gravitational pull. As the moon and Earth move, the moon's gravitational pull causes Earth and its oceans to bulge out directly toward the moon and directly away from the moon. These two bulges are the high tides, and areas far from these bulges will be the low tides.

The strength and timing of tides are also controlled by the sun's gravitational pull, the moon's orbit around Earth, Earth's tilt, weather, geography, and more. These many factors can make tidal predictions complicated.

The relationship between the moon's position, the sun's position, and a location on Earth plays a huge role in how the height of a high tide or low tide changes over time. The sun affects the tides just like the moon, but only with about half the power.

When the sun and moon align relative to Earth (at a full moon or new moon), their tidal bulges will add together. This added power will create higher high tides and lower low tides. When the sun and moon do not align with Earth, tidal effects are more muted.

Even the elliptic shape of Earth's orbit around the sun and the moon's orbit around Earth can cause tidal differences. In January, the Earth is physically closer to the sun (perihelion) and experiences more of the sun's gravitational power; similarly, once a month, the moon is closer to the Earth than it is any other time (perigee). A "king tide" (not a scientific term) can occur when the Earth is physically closer to both the sun and the moon at the same time and also experiencing a full or new moon. These king tides typically cause the largest tidal range of the year.

Of course, weather can modify the final effect of these astronomical events.

Since the moon's position and pull is largely responsible for the tides, the time the moon takes to move through the sky is important to know in predicting tides. It takes about 24 hours and 50 minutes for the moon to return to the same meridian (longitude line) in the sky as Earth rotates (also known as the moon's "apparent orbit" from Earth).

During this "tidal day", many coastal locations on earth such as Wells will experience two high tides and two low tides — two times where the ocean around Wells bulges toward or away from the moon, and two times where water flows away. The time between two high tides and the time between two low tides should be half a tidal day: roughly 12 hours and 25 minutes.

This timing, however, is not exact. As discussed before, many other factors can influence the tides. These factors can change both the height and timing of high and low tides.

Earth's geography can even cause some coastal locations to regularly experience fewer than two tides a day or to experience irregular high and low tide times.

NOAA (National Oceanic and Atmospheric Administration) is responsible for the recording and sharing of both weather and tidal data in the United States.

NOAA uses data recording stations to collect measurements and send them to servers for processing. A NOAA data recording station is set up at the Wells town pier, though at this time its data is not accessible. Instead, this app makes use of the NOAA station in Portland, Maine to get measurements and scale them to what can be expected in Wells.

NOAA also runs the Gulf of Maine Operational Forecast System (GoMOFS) to create advanced predictive models that can be more accurate than traditional tide charts. Traditional tide charts account only for the sun, the moon, and Earth's rotation; GoMOFS attempts to account for water level changes due to additional factors like wind, atmospheric pressure, and river flow.

Many weather apps and services rely on the data NOAA provides, whether observational or predictive.