Tides & Lunar-Solar Alignment

How Tides Work

• Tides are the regular up and down movement of ocean water.

  • When the water level is at its highest, it's called high tide.

  • When the water level is at its lowest, it's called low tide.

• The main reason for tides is the pulling forces (gravity) between Earth, the Moon, and the Sun.

• These pulling forces make the ocean water bulge out. There's a bulge on the side of Earth closest to the Moon (and Sun), and another bulge on the side directly opposite. These bulges are the high tides.

• The difference in height between a high tide and the next low tide is called the tidal range.

• Even though the Sun is much bigger than the Moon, it's so much farther away that its pulling effect on tides is smaller. • About how much each pulls:

  • Moon
    ≈ 54% of the total pulling force that creates tides.

  • Sun
    ≈ 46% of the total pulling force that creates tides.

• Important words to know: syzygy, spring (king) tide, neap tide.

Basics of Gravity

• The basic rule that explains why things pull on each other, called Newton's Law of Gravity, also explains tides:

  F = G\frac{m1 m2}{r^2}

  • F = the pulling force.

  • G = a special number for gravity.

  • m1, m2 = the sizes (masses) of the two objects pulling on each other.

  • r = the distance from the middle of one object to the middle of the other.

• Because the pulling force gets much weaker the farther things are apart, even a small change in distance can make a big difference in how strong the pull is. For example, when the Moon is a little closer to Earth (this is called perigee), its pull on the tides gets much stronger.

Syzygy: When Sun, Moon, and Earth Line Up

• What it means: when the Sun, Moon, and Earth are almost in a straight line.

• Happens during both the new moon and full moon.

• Why it's important: It makes the pulling forces of the Sun and Moon work together most strongly, leading to the highest high tides and lowest low tides.

Spring (King) Tides

• Also commonly known as king tides.

• What they are like:
  • The biggest difference between high and low tide each month (very high high tides and very low low tides).
  • Caused by syzygy.
  • Can lead to floods near the coast, beaches washing away, and stronger storm surges.

• Helpful hint: “Spring” here means the tides “jump up”; it's not about the season.

Neap Tides

• Happen when the Sun and Moon are at a 90-degree angle to Earth (like an 'L' shape).

  • This means that when you look from Earth, the Sun is in one direction (for example, straight ahead), and the Moon is directly to your side, forming a 90-degree angle. This happens during the first and third quarter moon phases.

• Their pulling forces partly work against (or cancel out) each other, making the difference between high and low tide very small.

• Neap tides are like “nipped” tides: the high tides aren't very high, and the low tides aren't very low.

Quick Comparison

Real-World Importance

• People managing coastal areas need to plan for king tides when building things (like roads and buildings), deciding how tall sea walls should be, and planning how to get people to safety. This means making sure water can drain away, raising buildings, and protecting swampy areas near the coast.

• Maps that show where floods might happen often use king tide information to guess what future sea levels might be like, which helps predict places that might be underwater all the time later.

Fast Look-Up List

• Syzygy: When Earth, Moon, and Sun are in a straight or nearly straight line.

• Spring (King) Tide: The biggest up and down movement of tides each month; happens during syzygy.

• Neap Tide: The smallest up and down movement of tides each month; occurs when Sun and Moon are at right angles relative to Earth.