WHY WE HAVE SEASONS ON EARTH Tahoma Jr. High 8 th Grade Science Maple Valley, WA

Why do some parts of Earth get colder during January, while others are having their summer? Ever notice the daylight hours are much shorter than in summer? New Zealand has a similar climate to Seattle, yet look at how Kiwis celebrate the holidays!

By knowing these simple facts, it’ll tell you it can’t be because of simple distance to the Sun or the whole planet would have summer at the same time. In fact, in our hemisphere, we are 3% CLOSER to the Sun during winter!

Something else must be happening. Could it have something to do with how Earth is positioned other than distance? Could it have something to do with why the Sun is so low in the sky during winter? Or that the North and South Poles can have six months of darkness followed by six months of daylight? What would do this?

From top down view, here’s how the Poles get 6 months of darkness followed by six months of light. This will happen anywhere within the Arctic or Antarctic circles.

Yes! Earth is tilted on its axis!! (remember when you’ve seen globes, they are tilted!)

Being tilted, Earth receives light at the Poles on a sharp angle, spreading the available light over a larger surface area. (watch what happens when you shine a flashlight on a bright surface at a sharp angle) Lower amounts of energy received per unit of surface area mean lower temperatures.

Therefore, areas near the Equator receive lots of energy per unit of surface area throughout the year (the Sun is basically always overhead). This is why tropical areas have temperatures that stay more the same throughout the year.

More direct sun + more hours of sun = warmer temps

Less direct sun + less hours of sun = lower temps

Northern Hemisphere would have opposite seasons to Southern Hemisphere. During Fall and Spring, day and night hours are equal (equinoxes).

WHAT CAUSES TIDES? WHY WOULD THE WATER BULGE UP AT CERTAIN TIMES? COULD IT BE GRAVITY PULLING ON IT? WHERE WOULD THE GRAVITY COME FROM?

The Bay of Fundy in eastern Canada has the largest tide changes in the world (up to 50 feet!). What causes this?

There are three major gravity fields affecting the oceans: 1.The Earth’s gravity (which keeps the water on the planet) 2. The Moon, a nearby large object 3. The Sun, a distant, but VERY big object

The Earth rotational spin causes water to bulge out, but the Moon’s gravity also causes bulges.

The Moon’s orbit angle to the Earth is not always near the Equator.

As the Earth rotates under the Moon and the Moon orbits the Earth, Moon’s gravity pulls on the water. MOON

Gravity depends on the mass creating it, but also a major contributor is DISTANCE. Even though the Sun is HUGE, it is so far away that the Moon will have a greater effect (Sun only has 33% tidal influence).

Water will bulge towards the Moon a lot, while it’ll bulge towards the Sun a little.

The Bay of Fundy has another factor to increase its tidal change besides normal spin and gravity – the shape of the bay contributes as well. So much water enters the bay so quickly that the Earth’s crust actually tilts a little bit due to the massive weight of the water!

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