Tides

Objectives:

1. Explain how the sun and moon affect tides.

2. Compare and contrast tidal ranges of different bodies of water.

Key terms:

tides perigee apogee spring tide neap tide

Notes:

Tides are periodic waves that are caused by the Moon and the Sun's gravitational pull on large bodies of water. High and low tides occur twice daily and can be predicted fairly accurately by the position of the sun and moon relative to large bodies of water.

Influences by the moon & sun

High tides

a direct high tide occurs as water rises up toward the moon as it is centered over large bodies of water

an indirect high tide occurs on the opposite side of the Earth as Earth's gravitational mass is directed toward the moon

full & new moon (full moon occurs at noon)

	creates the spring tide as the sun adds to the moon's gravitational pull
	highest tides are created if the moon is at perigee (closest point to the earth) and a new moon is present

moon is at quarter phase (right angle to the sun)

	creates the neap tide as the sun detracts from the moon's gravitational pull
	neap tides are very mild high tides
	lowest high tides are created when the moon is at apogee (farthest point from the earth) and a quarter moon is present

Low tides

low tides are created at right angles to the high tides as water is moved to areas of high tide

full & new moon (full moon occurs at noon)

	creates the low tides at right angles to the sun & moon as water is pulled toward the spring tide
	lowest tides are created if the moon is at perigee (closest point to the earth)

moon is at quarter phase (right angle to the sun)

	creates the highest low tide as the sun detracts from the moon's gravitational pull
	highest low tides are created when the moon is at apogee (farthest point from the earth) and a quarter moon is present

Tides

(http://images.google.com/imgres?imgurl=home.hiwaay.net/~krcool/Astro/moon/moontides)

The tidal range is defined as the shoreline distance the that the water travels during high and low tides. The tides appear 50 minutes later each day as the moon moves 13^o relative to the Earth per day.

Last modified: February 11, 2004