Key Concepts•What are solar and lunar eclipses?•What causes the tides?

Seasons, eclipses, and tides

WHY DO WE HAVE SEASONS? Seasons are the result of the tilt

of the Earth's axis. Earth’s axis is tilted 23.5°. This tilting is why we have

SEASONS like fall, winter, spring, summer.

The number of daylight hours is greater for the hemisphere, or half of Earth, that is tilted toward the Sun.

SOLSTICESSOLSTICES Solstices occur twice a year, when the tilt

of the Earth's axis is oriented directly towards or away from the Sun, causing the Sun to appear to reach its northernmost and southernmost extremes.

Winter solstice is the shortest day of the year. In the Northern Hemisphere. It occurs on December 21 and marks the beginning of winter.

The Summer Solstice is the longest day of the year. It occurs on June 21 and marks the beginning of summer.

SOLSTICE During the winter the

Northern Hemisphere day lasts fewer than 12 hours and the Southern Hemisphere day lasts more than 12 hours.

During the winter solstice, the North Pole has a 24-hour night and the South Pole has a 24-hour day.

Sunlight strikes the earth most directly at the Tropic of Capricorn.

http://k12.ocs.ou.edu/teachers/reference/solstice.gif

EQUINOXES

A day lasts 12 hours and a night lasts 12 hours at all latitudes.

Equinox literally means "equal night".

Sunlight strikes the earth most directly at the equator.

This occurs twice a year.

http://k12.ocs.ou.edu/teachers/reference/equinox.gif

EQUINOX The vernal

(spring) equinox occurs March 21.

The autumnal (fall) equinox occurs September 21.

Occurs when: moon’s shadow hits Earth or Earth’s shadow hits moon When an object in space comes

between the sun and a third object it casts shadow on that object = eclipse

New moon – moon is between sun and Earth

Most months the moon is a little above or below sun in the sky.

Solar eclipse occurs when the moon passes directly between the Earth and sun, blocking light from the sun

Not safe to look at the sun during a partial eclipse because an extremely bright part of the sun remains visible

During the full moon when the Earth is directly between the sun and moon

Moon is in Earth’s shadow

Earth’s shadow has an umbra and penumbra

When moon is in Earth’s umbra – you see a total lunar eclipse

Can see total lunar eclipse from anywhere on Earth

Most lunar eclipses, Earth, the moon and the sun are not quite in line = partial lunar eclipse

Brainpop: Eclipses

Youtube: Eclipse

Rise and fall of ocean water that occurs every 12.5 hours

Water rises for 6 hours and then falls for 6 hours

Caused by differences in how much the moon’s gravity pulls on different parts of Earth

Bay of Fundy Tides Video

High tides occur on the side of the Earth closest to the moon due to the moon’s gravity pulling on the water

High tides also occur on the side of the Earth farthest from the moon. The moon’s gravity pulls on the Earth more strongly than it pulls on the water leaving it behind

In between the two high tides, low tides occur

Study Jams video

STOP

Pick up from here after moon phases

Sun’s gravity pulls on Earth’s waters

During a new moon – sun, moon and Earth are nearly in a line.

Gravity of sun and moon pull in same direction

Combination of forces produce tide with greatest difference between low and high tide

Called a spring tide – occur twice a month during full and new moons

During moon’s 1st and 3rd quarter, line between Earth and the sun is at right angles to line between Earth and moon.

Sun’s pull is at right angles to moon’s pull.

Produces a neap tide = least difference between high and low tide

Occur twice a month