Tides are caused by the combined gravitational forces of the sun and moon on Earth's oceans. There are two types of tides: spring tides that occur during a new or full moon when the sun and moon are aligned, producing the highest high tides and lowest low tides; and neap tides that happen during a first quarter or third quarter moon when the sun and moon are at a right angle, resulting in smaller tidal ranges with higher low tides and lower high tides than normal.

1. Tides

2. Different kind of tides
Monthly tidal cycle based on Earthsun-moon position
Spring & Neap tides

3. Moon phase: New
or Full
Spring Tide
moon
earth
- Sun, Earth, and Moon are all aligned
- gravitational force of the moon and sun combine
- Highest high tide and lowest low tide
- Greatest tidal range
sun

4. Spring Tide
Moon phase: New or Full

5. Moon phase: First Quarter or Third Quarter
Neap Tide
sun
earth
moon
- Sun and Moon are at a right angle (perpendicular)
- gravitational force of the moon and sun partially cancel
- High tides are lower and Low tides are higher than normal
- moderate tidal range

6. Neap Tide
solar tide partially cancels out lunar tide
Moon phase: 1st Quarter & Third Quarter

7. Sun and moon effects can be additive or not…

8. Draw in the tidal bulges
moon
sun
earth

9. moon
earth
sun

10. moon
earth
sun