Earth, moon, and the sun

Key terms:  Solstice: day when the sun appears farthest North or South of the equator. Northern hemisphere receives the most sunlight of the year around June 21 on the summer solstice.  Phase: shape of the moon you see from Earth. shadow hits Earth during a solar eclipse  solar eclipse: when the moon passes directly between Earth and the sun, blocking sunlight from Earth. The moon’s shadow hits Earth during a solar eclipse  Spring tide: A tide with the greatest difference between consecutive low and high tides produced by gravity of Sun, Moon, and Earth

 What are Earth’s two main motions called? rotation and revolution.  What is rotation? The spinning of Earth on its axis.  What is Earth’s axis? An imaginary line that passes through its center and the North and South Poles.  How long does it take for Earth to make one rotation? 24 hours.  What change do we see as a result of Earth’s rotation? Day and night.

Earth-Sun interactions  As Earth rotates, how does the interaction of Earth and the sun affect day and night? Earth’s rotation causes the day and night as different sides of Earth face toward and away from the sun.  As Earth revolves how does the interaction of Earth and the sun affect how we mark time?  a year is the time it takes Earth to complete one revolution of the sun.

 The tilt of Earth’s axis and Earth’s changing position as it revolves around the sun cause seasons.  At what angle is Earth’s axis tilted? 23.5° from the vertical.  What would happen if Earth’s axis were straight up and down? Temperatures in a particular area would remain fairly constant year round.  Does the North Pole point in different directions as Earth revolves around the sun? No, the North Pole always points in the same direction.  In which hemisphere is the area of strongest sunlight? Southern Hemisphere.  What season is there? Summer  Where would the circle(each location where sunlight is shown) be on the first day of spring? Over the equator.

Seasons  Is the angle of the tilt different at different points in Earth’s revolution? No  What is different? Whether the north end of the axis is tilted toward or away from the sun.  What season is it in the northern hemisphere when the north end of the axis is pointed the most directly toward the sun? Summer  What season is it in the northern hemisphere when the south end of the axis is pointed the most directly toward the sun? Winter  When it is winter in the northern hemisphere, what season is it in the southern hemisphere? Summer

 The sun appears farthest north of the equator once each year and farthest south once each year. Each of these days is known as a solstice.  The day when the sun appears farthest North is the summer solstice in the Northern Hemisphere and the winter solstice in the Southern Hemisphere.  June 21 each year the sun is at its maximum height in the Northern Hemisphere-known as the June solstice. It is the longest day of the year in the Northern Hemisphere and the it is the shortest day of the year in the Southern Hemisphere.  December 21 the sun appears farthest south and the sun is at its minimum height at the Northern Hemisphere-known as the December solstice.  Equinox means equal night. During an equinox day and night are each about 12 hours long everywhere.  Spring equinox happens around March 21. It is the beginning of spring in the northern hemisphere. Fall equinox happens around September 22. It is the beginning of fall in the northern hemisphere

 What two conditions cause it to be summer in the northern hemisphere? In June, the sun shines more directly on the surface. The sun is above the horizon for a longer period each day.  What are two conditions that cause it to be winter in the Northern Hemisphere? In December, the sun shines less directly on the surface. The sun is above the horizon for a shorter period each day.

 Homework:  Explain how seasonal changes in temperature and hours of daylight relate to changes in Earth’s position as it moves around the sun.