Sunlight and Earth's Energy Balance

• Sunlight is the source of weather on Earth and its energy drives the Earth system.

Light and Energy from the Sun

• Only about half of the sunlight that reaches Earth's atmosphere makes it to the surface, the rest is absorbed or reflected.
• The specific parts of the electromagnetic spectrum that reach Earth's surface are infrared and visible light, along with a very small amount of ultraviolet light.
• Sunlight consists of waves of energy with varying wavelengths; shorter wavelengths have more energy.
• Ultraviolet light has more energy and a shorter wavelength than visible light, but most of it is blocked by the ozone layer in the stratosphere.
• Visible light is detectable by human eyes, has less energy than ultraviolet light, and includes all colors of the rainbow.
• Infrared light has a longer wavelength and less energy than visible light, and when absorbed by the skin, it feels warm.

The Greenhouse Effect

• Earth's temperature is "just right" to support life due to the chemical composition of its atmosphere.
• Visible light penetrates the atmosphere and warms Earth's surface.
• The warmed surface emits infrared light, which has longer wavelengths and less energy compared to visible and UV light.
• Greenhouse gases like carbon dioxide, methane, and water vapor absorb the energy of infrared light, trapping it in the atmosphere and increasing atmospheric temperature.
• The greenhouse effect is the warming of the atmosphere (specifically the troposphere) due to energy trapped by greenhouse gases, subsequently warming Earth’s land and water.

Sunlight and Earth's Shape

• Sunlight travels in straight lines (rays) but does not strike Earth's surface at the same angle due to Earth's curvature.
• Near the equator, rays strike Earth perpendicularly (at a right angle), while towards the poles, the angles are nonperpendicular, resulting in less concentrated light.
• Latitude measures a position on Earth relative to the equator.
• Regions near the equator (0° latitude) receive the most direct sunlight and energy, while higher latitudes receive less direct sunlight.
• Sunlight energy is spread over a larger area near the poles due to the low, slanted angle of the rays.

The Uneven Heating of Earth

• Thermal energy flows from locations of high temperature to low temperature.
• Energy travels from the warmer equatorial regions towards the poles through motion in the atmosphere and oceans.
• This flow of energy moderates temperature differences between latitudes, making the poles less cold and the equator less hot, which is important for life.
• The atmosphere and ocean move energy around Earth by convection, affecting weather, land, and living things.

The Seasons

• Changes in the angle at which sunlight strikes Earth cause the seasons.
• Earth's axis is tilted at 23.5° relative to its orbit around the sun, and the part of Earth tilted toward the sun changes throughout the year.
• When the Northern Hemisphere tilts toward the sun in June, it receives more direct sunlight and energy, resulting in summer with warmer temperatures and longer days.
• At the same time, the Southern Hemisphere tilts away from the sun, receiving less energy, resulting in winter with shorter days and colder weather.
• The opposite occurs in December, when the Northern Hemisphere tilts away from the sun.

Cooking with Solar Energy

• A solar cooker uses sunlight to heat food to high enough temperatures for cooking.
• Engineering students designed a solar cooker for refugee camps, which needed to collect and retain solar energy to cook food.
• Criteria for the solar cooker included ease of use, ability to cook one-pot meals for a small family, and reaching a temperature of at least 85°C.
• Constraints included low cost and minimal space usage.
• Two designs were tested, a solar oven box and a parabolic solar cooker.
• A panel cooker was designed combining the best features of both models
• Students found that a panel cooker was best as it didn't need repositioning, was easy to use, inexpensive and easy to store.

Reading Further: The Goldilocks Zone

• The Goldilocks zone is the area around a star where temperatures are suitable for liquid water to exist on a planet's surface.
• Liquid water is essential for life as we know it, making planets within a star's Goldilocks zone potentially habitable.
• The sun sits in the center of our solar system, it gives off energy that warms Earth, allowing liquid water to exist on Earth’s surface
• Stars get their energy from fusion reactions, converting matter into thermal energy.
• If Earth were closer to the sun, a runaway greenhouse effect would occur, causing all water to evaporate and temperatures to become too high for life.
• NASA announced the discovery of the TRAPPIST-1 system, which has seven Earth-sized planets, with at least three in the star’s Goldilocks zone, making them potential candidates for finding liquid water.