The Earth and the sky are fundamental parts of our natural world. This lesson will explore these concepts from the perspectives of astronomy and Earth science, explaining how they interact and affect each other. While it may seem that the Earth and the sky are separate domains, they are interconnected in many ways that impact the environment, climate, and life on Earth.
Our planet, Earth, is one of the eight planets in the Solar System, orbiting the Sun once every 365.25 days. The Earth's axis is tilted at an angle of about 23.5 degrees relative to its orbit around the Sun. This tilt is responsible for the changing seasons as the Earth orbits the Sun. The hemisphere that is tilted towards the Sun experiences warmer temperatures and longer days, marking the summer season, while the opposite hemisphere experiences winter.
The Earth's atmosphere is a layer of gases that surrounds the planet, protecting it from harmful radiation from the Sun and helping to regulate temperature. The atmosphere is composed mainly of nitrogen (78%) and oxygen (21%), with small amounts of other gases such as argon and carbon dioxide. The atmosphere is divided into several layers, from lowest to highest: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Each layer has its own characteristics and functions, such as the ozone layer in the stratosphere, which absorbs and scatters ultraviolet solar radiation.
The sky is the Earth's atmosphere as seen from the planet's surface. When we look up, we see the blue sky during the day because of the scattering of sunlight by the atmosphere. This scattering is more effective for shorter wavelengths of light (blue) than for longer wavelengths (red). At sunrise and sunset, the light has to pass through more of the Earth's atmosphere, resulting in the scattering out of much of the blue light and leaving the sky looking red or orange.
At night, when the part of the Earth you are on faces away from the Sun, you can see the stars, planets, and the Moon. Stars are huge, distant suns that emit light, while planets, such as Venus and Mars, are closer to Earth and shine by reflecting sunlight. The patterns that stars appear to form in the sky are known as constellations, which have been used for navigation and telling stories throughout human history.
The Moon, Earth's only natural satellite, goes through different phases based on its position relative to the Earth and the Sun. These phases include the New Moon, when it is aligned between the Earth and the Sun; the Full Moon, when the Earth is between the Moon and the Sun; and the first and last quarters, when we see half of the Moon illuminated. The cycle of phases repeats every 29.5 days.
As the Earth orbits the Sun, the visible constellations in the night sky change. This is because the nighttime side of the Earth faces different parts of space at different times of the year. Additionally, the position of the Sun in the sky changes throughout the year, reaching its highest point at the summer solstice and its lowest at the winter solstice.
An eclipse occurs when the Earth, Moon, and Sun align. During a solar eclipse, the Moon passes between the Earth and the Sun, casting a shadow on the Earth and temporarily blocking the Sun's light in some areas. During a lunar eclipse, the Earth is between the Sun and the Moon, and the Earth's shadow falls on the Moon. Solar eclipses can only occur during a New Moon, while lunar eclipses occur during a Full Moon.
Light pollution, caused by excessive artificial light, can significantly reduce the visibility of stars in the night sky. This is particularly noticeable in urban areas, where the concentration of artificial lighting makes it difficult to observe all but the brightest stars and planets.
The Earth and the sky are closely intertwined, offering us a window into the broader universe and our place within it. From understanding the basics of Earth's atmosphere and its movement in space to observing the stars, planets, and the Moon in the sky, there is always something new to discover. Although light pollution has made it more challenging to observe the night sky, there are still many places and times when the wonders of the universe are visible to the naked eye, reminding us of the beauty and complexity of the world we live in.
