![]() Only half the Earth is ever lit by the Sun at one time, which halves the total solar irradiance. The total solar irradiance is the maximum possible power that the Sun can deliver to a planet at Earth’s average distance from the Sun basic geometry limits the actual solar energy intercepted by Earth. ![]() If for just one hour, you could capture and re-use all the solar energy arriving over a single square meter at the top of the atmosphere directly facing the Sun-an area no wider than an adult’s outstretched arm span-you would have enough to run a refrigerator all day. How much power is 1,360 watts? An incandescent light bulb uses anywhere from 40 to 100 watts. (Before scientists discovered that it varies by a small amount during the sunspot cycle, total solar irradiance was sometimes called “the solar constant.”)Ī watt is measurement of power, or the amount of energy that something generates or uses over time. This amount of power is known as the total solar irradiance. ![]() At Earth’s average distance from the Sun (about 150 million kilometers), the average intensity of solar energy reaching the top of the atmosphere directly facing the Sun is about 1,360 watts per square meter, according to measurements made by the most recent NASA satellite missions. At that temperature, most of the energy the Sun radiates is visible and near-infrared light. At the same time, the Southern Hemisphere is tilted away from the sun and experiencing winter.The surface of the Sun has a temperature of about 5,800 Kelvin (about 5,500 degrees Celsius, or about 10,000 degrees Fahrenheit). When the Northern Hemisphere is tilted toward the sun, latitudes between the equator and 90°N (the North Pole) are experiencing summer. The combination of more direct rays of sunlight and more hours of daylight causes the hemisphere tilted toward the sun to receive more solar radiation and to have warmer temperatures. The hemisphere tilted toward the sun also has more hours of daylight than the hemisphere that is tilted away from the sun. Whichever hemisphere (the Northern or Southern Hemisphere) is tilted toward the sun receives more direct rays of sunlight (or rays that are closer to perpendicular or a 90° angle). Earth is actually a little farther from the sun when the Northern Hemisphere is having summer. ![]() This is a misconception because Earth's orbit is only slightly elliptical and our planet is nearly the same distance from the sun all year long. People often mistakenly think that the different seasons are caused by a change in Earth's distance from the sun. Similar to the previous graphic but this perspective is vertical and looking down at the North Pole. Because the direction and angle of the axis of rotation do not change, the Northern Hemisphere is tilted toward the sun during part of the year and away from the sun during another part of the year. The direction and angle (or tilt) of Earth's axis of rotation do not change as Earth revolves around the sun. When we add a day every 4 years to align the calendar, this year is often called a leap year.Īt the present time, Earth is tilted on its axis of rotation by 23.5°. To keep our calendars synchronized with the planet's actual orbit, every 4 years we add an extra day to the month of February – 4 quarters of a day (1 quarter each year for 4 years) equals 1 day or 24 hours. Earth takes 365 and ¼ (6 hours) days to complete one revolution around the sun. Like the other planets, Earth rotates on its axis as it revolves around the sun. ![]() This is a horizontal perspective facing the equator. This graphic shows Earth with its 23.5° tilt, the direction of its rotation and the pattern of the seasons as it travels around the sun. ![]()
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