Topic 4

What are tides?

• Tides are cyclic rises and falls of ocean water. The cycle takes about 24 hours and 50 minutes

• Ocean tides occur 4 times a day: 2 highs and 2 lows each day

What causes tides?

The tides are caused by the gravitational; attraction between Earth, moon and the sun (Although the moon has a stronger gravitational pull because its closer)

Where and when does high tide occur?

High tide occurs on the sides of the earth that are aligned with the moon. It occurs twice a day.

Where and when does low tide occur?

Low tide occurs on the sides of the Earth that is at a right angle to the places having high tides. It also occurs twice a day.

How long does it take to gofrom one high tide to the next?

• A complete tide cycle of 2 highs and 2 low tides take 24 hours and 50 minutes and the tides switch from High to Low to High to Low.

• Therefore, it takes about 12 hours and 25 minutes to go from one high tide to the next

What is a spring tide?

• A spring tide is a tide that produces high tides that are higher than normal and low tides that are lower than normal.

• It occurs when the Sun, moon and Earth are all aligned.

During what phases ofthe moon does a spring tide occur?

New and Full Moons

What is a neap tide?

A tide that produces tides that are not as high or low as normal. (moderate changes)

During what phases ofthe moon does a neap tide occur?

First and Third Quarter

What is an eclipse?

• When a celestial object partially or completely comes into the shadow of another celestial object.

• There are two types of shadows:

- An Umbra and a Penumbra• An Umbra is the darker part of the shadow• A Penumbra is the lighter part of the shadow

What is a lunar eclipse • When the moon moves into the shadow of the Earth.• Visible by all people having night• Can last up to 100 minutes• There are two lunar eclipses per year

During what phase of themoon does a lunar eclipse occur?

A Lunar eclipse can occur during the Full moon phase.

What is a solar eclipse?

• When the moon blocks out the sun by casting a shadow on Earth.

• Can last up to 7 1/2 minutes• Occurs once every 200 years for any given

location.

During what phase of themoon does a solar eclipse occur?

A solar eclipse can occur during the New Moon phase.