THE EARTH, SUN, & THE MOONText 8.3

Agenda1. Earth’s Rotation 2. The Moon 3. Solar Eclipses4. Tides

Earth’s Rotation: Day & Night

The Sun rises in the East and sets in the West every day, but why does this happen?

The Earth is spinning on its axis.

Earth’s Rotation The Earth spins on its axis in a manner

similar to a top. Every day the Earth makes one complete

rotation in a west-to-east direction.

Earth’s Rotation The portion of Earth that faces the sun

experiences daylight, while the portion that faces away experiences darkness.

While the Earth is spinning it also orbits around the Sun in its Orbital Radius.

Orbital Radius -The average distance between an object in the Solar System and the Sun.

Earth’s Rotation

Earth’s Rotation The Earth takes 365.25 days to orbit

completely around the sun. Planets closer to the sun take less time

(Mercury 88 days), while ones that are farther away take more time (Mars 687 days)

The Earth is on a 23.5° tilt when compared to the Earth’s orbit around the sun. This tilt affects the daytime temperatures experienced by Earth’s hemispheres.

Earth’s Rotation

Northern and Southern hemispheres experience 4 seasons. When the Earth is farthest from the Sun, the Northern hemisphere is tilted towards the sun and the Northern Hemisphere experiences more hours of direct sunlight (Summer).

When the Northern hemisphere is tilted away from the sun we experience less hours of sunlight and the light is not as direct. (Winter)

Solstice – An astronomical event that occurs two times a year, when the tilt of Earth’s axis is most inclined toward or away from the sun, causing the position of the Sun in the sky to appear to reach its highest or lowest height in the sky.

Equinox – The time of year when the hours of daylight equal the hours of darkness.

A shadow is essentially a dark region that forms behind an object that is being illuminated more brightly on one side than the other.

We experience night when we are in the Earth’s shadow. The other side of the Earth is reflecting and absorbing all of the sunlight that strikes it.

Phases of the moon

The light that strikes the moon also affects how we see the moon depending on the moons position.

In the diagram below the sunlight is approaching from the right. The Earth is pictured in the center and the moon is seen orbiting around it in eight stages.

In each stage, half of the moon is always receiving light from the sun. In some of the phases, we see the sunlit portion as well as the shaded portion. This makes the moon appear as though some of it has disappeared

The moon passes through 8 stages over a period of around 4 weeks and is known as a lunar Cycle.

Eclipses An eclipse is an astronomical event that

occurs when a celestial object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer.

There are two types of eclipses that we experience here on Earth:

1. Solar Eclipse 2. Lunar Eclipse

Solar Eclipse

A solar eclipse occurs when the Moon passes in front of the Sun as seen from the Earth. The type of solar eclipse event depends on the distance of the Moon from the Earth during the event.

A total solar eclipse occurs when the Earth intersects the umbra portion of the Moon's shadow.

When the umbra does not reach the surface of the Earth, the Sun is only partially occluded, resulting in an annular eclipse.

Partial solar eclipses occur when the viewer is inside the penumbra

Lunar Eclipse Lunar eclipses occur when the Moon

passes through the Earth's shadow. Since this occurs only when the Moon is on the far side of the Earth from the Sun, lunar eclipses only occur when there is a full moon. Unlike a solar eclipse, an eclipse of the Moon can be observed from nearly an entire hemisphere.

A lunar eclipse also lasts longer, taking several hours to complete, with totality itself usually averaging anywhere from about 30 minutes to over an hour compared to around 7 minutes for a total solar eclipse.

There are three types of lunar eclipses:

1. penumbral, when the Moon crosses only the Earth's penumbra;

2. partial, when the Moon crosses partially into the Earth's umbra;

3. Total, when the Moon circles entirely within the Earth's umbra.

Total lunar eclipses pass through all three phases.

Even during a total lunar eclipse, however, the Moon is not completely dark. Sunlight refracted through the Earth's atmosphere intersects the umbra and provides a faint illumination

Tides Tide – The alternate rising and

falling of the surface of large bodies of water; caused by the interaction between Earth, the Moon, and the Sun.

The gravitational pull of the sun and moon affect the coastal areas, this causes water to become deeper in some areas of the Earth (high tide) and other areas become more shallow (low tide). The moon has a greater effect on tides as it is closer to Earth.

The largest tides occur when the Sun and Moon are in line with the Earth. These are known as Spring tides.

Neap tides occur when the moon is at a right angle to the Earth and Sun, these tides are much weaker as the gravitational pull of the Moon and the Sun counteract each other.

The Bay of Fundy in Nova Scotia has the world’s largest tides of 15 metres.

Questions: Page 328 # 1-3, 8, 9. 10, 12, 13, 14