Why do we have seasons?

Vocabulary Axis: the angle between an object’s rotational axis, and a line perpendicular to its orbital plane. Tilt: moving into a sloping position Seasons: Each of the four divisions of the year ( spring,summer,autumn,and winter) marked by particular weather patterns and daylight hours, resulting from the earth’s changing positions with regard to the sun.

Summer solstice: marks the onset of summer, at the time of the longest day, about June 21 in the northern hemisphere and December 22 in the southern hemisphere. Winter solstice: marks the onset of winter, at the time of the shortest day, about December 22 in the northern hemisphere and June 21 in the southern hemisphere

Earth’s rotation The Earth rotates on its axis every 23 hours & 56 minutes. The rotation of Earth causes day and night.

Earth’s revolution Revolution is the movement of one object around another. It takes the Earth 365 days to travel or revolve around the sun once. This is called a year.

Why do we have seasons? The Earth’s orbit around the sun is NOT a perfect circle. It is an ellipse. Seasons are not caused by how close the Earth is to the sun. In fact, the Earth is closest to the sun around January 3 and farthest away from the sun around July 4. Ellipse

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.

Summer Summer is warmer than winter (in each hemisphere) because the Sun's rays hit the Earth at a more direct angle during summer than during winter

Also the days are much longer than the nights during the summer. During the winter, the Sun's rays hit the Earth at an extreme angle, and the days are very short. These effects are due to the tilt of the Earth's axis.

Seasons…in a nut shell

Solstices 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. Tyrrhenian Sea and Solstice Sky Credit & Copyright: Danilo Pivato

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.

The seasons are the result of the tilt of the Earth's axis. I know this is a repeat, but it is important that you understand this idea. Many Americans, including Harvard graduates, do not know what causes seasons!

Season’s Review Questions Is the Northern Hemisphere pointed toward the sun or away from the sun during summer? What causes the seasons? At what angle is Earth tilted on its axis?

High or Low - What Causes Tides?

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What Are Tides? Tides are the daily rise and fall of Earth’s waters on its coastlines. As the tide comes in, the level of water on the beach rises, and as the tide goes out, the level of water on the beach goes down. Tides occur in all bodies of water, but they are most noticeable in the ocean and large lakes.

High Tides High tides are when the water reaches its highest point.

Low Tides Low tides are when the water reaches its lowest point.

What Causes Tides? Tides are caused by the interaction of Earth, the Moon, and the Sun. Gravity is the reason for tides. Gravity is the force exerted by an object that pulls other objects toward it.

Moon’s Gravity and Tides The Moon’s gravity affects the water on Earth’s surface. Since the Moon is close to the Earth, it has a strong gravitational pull on it (closer objects have stronger gravitational pull).

Moon’s Gravity – Tidal Bulges The Moon pulls on the water on the side nearest to it more strongly than it pulls on the center of the Earth. This pull creates a bulge of water, called a tide bulge, on the side of Earth facing the the Moon.

Moon’s Gravity – Tidal Bulges The water on the side of Earth facing away from the Moon has a less strong pull. This water is “left behind” and forms a second bulge. As Earth rotates, different places on the planet’s surface pass through the areas of the tidal bulges and have the change in water levels.

Tidal Bulges – High Tide In places where there are tidal bulges, high tide is occurring along the coastlines. High Tide High Tide

Tidal Bulges – Low Tide In places between the bulges, low tide is occurring. LOW TIDE LOW TIDE

Sun’s Gravity and Tides The Sun is so large that its gravity also affects tides. At times, the Sun and Moon pull together on Earth’s waters in the same direction. At other times they pull in different directions.

Daily Tide Cycle Most seashores have four tides every day – two high tides and two low tides. A change of from low to high tide or vice versa takes about 6 hours and 12 minutes. Changes in tides can be drastic (can notice) or or less dramatic (can’t notice).

Monthly Tide Cycle Changes in the positions of Earth, the Moon, and Sun affect the height of tides during a month.

Spring Tides Spring tides occur 2 times a month, during a full and new moon when the Earth, Sun, and Moon are lined up. Spring tides are higher and lower than normal tides. “strong tides”

Neap Tides Neap tides occur in between spring tides, at the first and third quarters of the Moon when the Sun and Moon pull at right angles to each other. Neap tides are not as high or low as normal tides. “weak tides”

Moon Phases

Half of the Moon is always lit up by the sun Half of the Moon is always lit up by the sun. As the Moon orbits the Earth, we see different parts of the lighted area.

The revolution of the Moon around the Earth makes the Moon look as if it is changing shape in the sky. 

This is caused by the different angles from which we see the lighted part of the Moon's surface.  These are called "phases" of the Moon. 

Orbit of the Moon • The time it takes the Moon to go through its phases is 29.5 days. • The time it takes the Moon to orbit the Earth with respect to the stars is 27.3 days. • The orbit of the Moon is inclined by 5degrees.

• The Moon shines by reflected sunlight. – On average, it reflects about 7% of sunlight. – The Moon appears about 400,000 times fainter than the Sun in the sky. -The phases of the Moon are the result of varying viewing angles throughout the month. – A common misconception is that the phases of the Moon are caused by the shadow of the Earth.

The Moon passes through four major shapes during a cycle that repeats itself every 29.5 days.  The phases always follow one another in the same order: New moon First quarter Third quarter Full moon

New Moon The lighted side of the Moon faces away from the Earth.  This means that the Sun, Earth, and Moon are almost in a straight line, with the Moon in between the Sun and the Earth.  The Moon that we see looks very dark

New Moon

First Quarter Moon The right half of the Moon appears lighted and the left side of the Moon appears dark.  During the time between the New Moon and the First Quarter Moon, the part of the Moon that appears lighted gets larger and larger every day, and will continue to grow until the Full Moon.

First Quarter Moon

Third (Last) Quarter Moon Sometimes called Third Quarter.  The left half of the Moon appears lighted, and the right side of the Moon appears dark.  During the time between the Full Moon and the Last Quarter Moon, the part of the Moon that appears lighted gets smaller and smaller every day. It will continue to shrink until the New Moon, when the cycle starts all over again.

Third Quarter Moon

Full Moon The lighted side of the Moon faces the Earth.  This means that the Earth, Sun, and Moon are nearly in a straight line, with the Earth in the middle.  The Moon that we see is very bright from the sunlight reflecting off it.

Full Moon

There are also four other phases of the Moon sometimes used.

("Waxing" means increasing, or growing larger.) Waxing Crescent Moon This Moon can be seen after the New Moon, but before the First Quarter Moon.  The crescent will grow larger and larger every day, until the Moon looks like the First Quarter Moon. ("Waxing" means increasing, or growing larger.)

Waxing Crescent Moon

Waxing Gibbous Moon This Moon can be seen after the First Quarter Moon, but before the Full Moon.  The amount of the Moon that we can see will grow larger and larger every day.  ("Waxing" means increasing, or growing larger.)

Waxing Gibbous Moon

Waning Gibbous Moon This Moon can be seen after the Full Moon, but before the Last Quarter Moon.  The amount of the Moon that we can see will grow smaller and smaller every day. ("Waning" means decreasing, or growing smaller.)

Waning Gibbous Moon

("Waning" means decreasing, or growing smaller.) Waning Crescent Moon This Moon can be seen after the Last Quarter Moon and before the New Moon.  The crescent will grow smaller and smaller every day, until the Moon looks like the New Moon. ("Waning" means decreasing, or growing smaller.)

Waning Crescent Moon

Waxing & Waning

MOON QUIZ!! kahoot

The Moon’s Motion Where would the moon's face appear in each view in this diagram that shows the moon's rotation and revolution?

What are eclipses The moon’s orbit around Earth is slightly tilted with respect to Earth’s orbit around the sun. As a result, the moon travels above and below Earth’s orbit. But on rare occasions, Earth, the moon, and the sun line up. When an object in space comes between the sun and a third object, it casts a shadow on that object, causing an eclipse to take place. There are two types of eclipses: solar eclipses and lunar eclipses.

Solar Eclipse A solar eclipse occurs at a new moon when the moon passes directly between Earth and the sun, blocking sunlight from Earth. The moon’s shadow then hits Earth. The moon’s shadow has two parts. The darker part is the umbra. The larger, lighter part is the penumbra. During a solar eclipse, the sun’s light is completely blocked to people within the umbra. They see a total solar eclipse. Part of the sun’s light remains visible in the penumbra. So people within the penumbra see a partial solar eclipse.

Solar Eclipse The diagram shows the moon’s penumbra and umbra during an eclipse.

Lunar Eclipse A lunar eclipse occurs at a full moon when Earth is directly between the moon and the sun. During a lunar eclipse, Earth blocks sunlight from reaching the moon. Lunar eclipses occur only when there is a full moon because the moon is closest to Earth at that time. Earth’s shadow also has an umbra and penumbra. When the moon is in Earth’s umbra, you see a total lunar eclipse. For most lunar eclipses, Earth, the moon, and the sun are not quite in line, and only a partial lunar eclipse occurs.

Lunar Eclipse As the moon moves through Earth’s shadow, total and partial eclipses occur.