For the Northern Hemisphere, the axis points most toward the sun in June specifically around June 21 , and away from the sun around December This corresponds to the Winter and Summer Solstice solstice is Latin for "the sun stands". For the Southern Hemisphere, this is reversed. For both hemispheres, the earth is 90 degrees away from the sun around March 21 and then again around September This corresponds to the Fall and Spring Equinox equinox is Latin for "equal night". Everyplace in the world has about 12 hours of daylight and 12 hours of night.
Day and night are not exactly of equal length at the time of the March and September equinoxes. The dates on which day and night are each 12 hours occur a few days before and after the equinoxes. The specific dates for this occurrence are different for different latitudes. On the day of the equinox, the geometric center of the Sun's disk crosses the equator, and this point is above the horizon for 12 hours everywhere on the Earth. However, the Sun is not simply a geometric point. Sunrise is defined as the instant when the leading edge of the Sun's disk becomes visible on the horizon, whereas sunset is the instant when the trailing edge of the disk disappears below the horizon.
At these times, the center of the disk is already below the horizon. Furthermore, atmospheric refraction or bending of the Sun's rays cause the Sun's disk to appear higher in the sky than it would if the Earth had no atmosphere. Thus, in the morning, the upper edge of the disk is visible for several minutes before the geometric edge of the disk reachs the horizon. Similarly, in the evening, the upper edge of the disk disappears several minutes after the geometric disk has passed below the horizon.
For observers within a couple of degrees of the equator, the period from sunrise to sunset is always several minutes longer than the night.
At higher latitudes in the Northern Hemisphere, the date of equal day and night occurs before the March equinox. Daytime continues to be longer than nighttime until after the September equinox. In the Southern Hemisphere, the dates of equal day and night occur before the September equinox and after the March equinox. The chart shown below shows the dates and times for the equinoxes and solstices through Times listed are in Eastern Time.
Subtract one hour for Central Time. Source: U. Naval Observatory. The answer is YES. Compared with how far away the Sun is, this change in Earth's distance throughout the year does not make much difference to our weather.
Earth's axis is an imaginary pole going right through the center of Earth from "top" to "bottom. That is why we have day and night, and why every part of Earth's surface gets some of each.
Long, long ago, when Earth was young, it is thought that something big hit Earth and knocked it off-kilter. So instead of rotating with its axis straight up and down, it leans over a bit.
By the way, that big thing that hit Earth is called Theia. It also blasted a big hole in the surface. That big hit sent a huge amount of dust and rubble into orbit. Most scientists think that that rubble, in time, became our Moon. Tell students that the Earth moves around the sun in an elliptical orbit and is tilted on its axis.
Explain that as Earth orbits the sun, it rotates on its axis, and the axis is always pointed in the same direction. Have the students representing the Earth and sun in each group stand approximately feet apart. Dim or turn off the lights. Use guided inquiry to have students investigate direct and indirect sunlight. First, have the student acting as the sun keep the flashlight pointed straight at the representation of Earth while the student holding Earth walks in a circle around the sun.
The Earth should stop when the pushpin representing a person in the Northern Hemisphere can "see" the sun. Ask: Is the sun more direct for the person at the top or the person at the bottom of the Earth?
Address any student misconceptions. One common student misconception is that this is due to the Northern Hemisphere being closer to the sun. Note that there is no significant difference in the distance of the sun to the Northern and Southern Hemispheres. The difference is due to direct and indirect solar radiation. The hemisphere that is pointed toward the sun receives more direct solar radiation, thus it is warmer. Ask: Is the sun more direct, or bright, for the person in the Northern Hemisphere or the Southern Hemisphere?
Southern Hemisphere Which person do you think feels warmer temperatures? Use guided inquiry to help students investigate the role of axis and tilt in the sun-Earth relationship.
Tape a black circle to the wall at that location to help students keep the axis pointed in one direction. Next, ask the Earth to resume orbiting the sun, while keeping the North Pole pointed at the black circle. Remind students to keep the sun stationary and pointed at Earth. Explain to students that the Earth's tilt does not change significantly over the course of a year, but does shift gradually over millennia. Have students stop the Earth after one-half of an orbit so that it is opposite of where it started.
It should be night for them if the Earth has orbited correctly, so the student will have to spin the Earth. Finally, ask groups to move the Earth half an orbit around the sun again, making sure to keep the North Pole pointed at the black circle. Make sure the sun does not move. Also, ensure as the Earth orbits the sun, the axis does not change orientation and continues pointing to the black circle.
Have students make a math connection. Have the rest of the students sit on the floor in a small area near the center of the classroom but facing the sun. Ask students to imagine that the floor is the Northern Hemisphere of the Earth. In the winter, the North Pole of the Earth is pointing away from the sun, so the sun appears farther south in the sky to us. Have the student hold the sun closer to the floor.
Have the rest of the class place their hands close to the floor and point toward the sun. Ask: Do your finger and the floor form a large or small angle? Then have the student holding the sun hold it up as high as he or she can. Have the rest of the class keep their hands close to the floor and again point to the sun. Ask: Is the angle you have formed with your finger and floor larger or smaller? Ask: What season does this represent? Point out to students that the seasons are opposite for people on the top north of the Earth and on the bottom south of the Earth.
Ask students to orally explain how the interaction between the sun and Earth affects seasons here on Earth, and what happens with the sun's rays during the different seasons. Encourage them to use vocabulary terms axis, tilt, direct sunlight, and indirect sunlight in their responses. Explain to students that every planet in our solar system has seasons.
But the seasons that occur on other planets are extremely different from the traditional spring, summer, autumn, and winter that we experience on Earth. Which would cause more extreme seasons—a smaller or larger tilt? Which would cause more extreme seasons—being closer or farther away? Then have them read a list from NASA about the length of seasons on other planets in our solar system.
One common misconception that students have about seasons is that seasons are due to how close or far the Earth is to the sun. When the Northern Hemisphere of the Earth is leaning toward the sun, it receives direct sunlight.
The warmth of direct rays causes spring and then summer in that part of the globe. When the Northern Hemisphere of the Earth is leaning away from the sun, it receives more indirect sunlight.
The cooling effects of more indirect sunlight cause autumn and winter.
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