That big hit sent a huge amount of dust and rubble into orbit. Most scientists think that that rubble, in time, became our Moon. As Earth orbits the Sun, its tilted axis always points in the same direction. It is summer in June in the Northern Hemisphere because the Sun's rays hit that part of Earth more directly than at any other time of the year.
It is winter in December in the Northern Hemisphere, because that is when it is the South Pole's turn to be tilted toward the Sun. And, believe it or not, aphelion when Earth is farthest from the Sun occurs in July, and perihelion when we are closest occurs in January. For those of us who live in the Northern Hemisphere where it's summer in July and winter in January, that seems backwards, doesn't it? One full circle around the lightbulb represents one full year on Earth.
As you move the ball around the lightbulb, try spinning it between your fingertips, so that the light always shines directly onto the equator. If the Earth span like this, day and night would be the same length all year round, and there would be no seasons. Now, take that small ball and tilt it at an angle, so that the light from the bulb no longer shines directly on the equator. If you are doing this at home, it might help to colour in either the top or bottom half of the ball.
Now the hemispheres of the ball will get different amounts of light at any one time. The hemisphere tilted away from the bulb gets less light, and the hemisphere tilted towards the bulb gets more.
Keeping the ball at the same angle, move it to the other side of the light bulb. The hemisphere that was tilted away from the bulb is now tilted towards it. The same thing happens as the Earth moves around the Sun, which is what gives us different seasons at specific times of the year.
Remember, the decrease in sunlight and colder temperatures you get during winter is not because the hemisphere is further away, but because the sun is above the horizon for a much shorter time.
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. In December, when the Northern Hemisphere is tilted away from the sun, with fewer hours of daylight.
Seasons have an enormous influence on vegetation and plant growth. Winter typically has cold weather, little daylight, and limited plant growth. In spring, plants sprout , tree leaves unfurl , and flowers blossom.
Summer is the warmest time of the year and has the most daylight, so plants grow quickly. In autumn, temperatures drop, and many trees lose their leaves. The four-season year is typical only in the mid-latitudes.
The mid-latitudes are places that are neither near the poles nor near the Equator. The farther north you go, the bigger the differences in the seasons. Helsinki, Finland, sees In mid-December, however, it is light for less than 6 hours. Athens, Greece, in southern Europe, has a smaller variation. It has Places near the Equator experience little seasonal variation.
They have about the same amount of daylight and darkness throughout the year. These places remain warm year-round. Near the Equator, regions typically have alternating rainy and dry seasons. Polar regions experience seasonal variation, although they are generally colder than other places on Earth.
Near the poles, the amount of daylight changes dramatically between summer and winter. In Barrow, Alaska, the northernmost city in the U. The city is in total darkness between mid-November and January. Seasons in Alaska Sometimes, seasons are determined by both natural and man-made activity. In the U.
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