My Science School

Earth is the third planet from the Sun in our Solar System. From a distance, it looks like a great, round, blue jewel hanging in the darkness of space. It is blue because three-quarters of its rocky surface is submerged under blue, ocean waters, which shimmer in the light of the Sun.

The way light reflects off air molecules has an effect on the way people see the sky as well as the ocean. When orbiting the Earth, satellites and astronauts see a blue globe due to some of these same properties. The sheer amount of water on Earth makes it appear blue in these instances, but there are other factors as well.

Scattering in the Atmosphere

The atmosphere is predominantly made of two gases, nitrogen and oxygen. These molecules absorb and scatter, or radiate, different kinds of light. Red, yellow and orange light have longer wavelengths that are not affected by as much by atmospheric gases, so they are not absorbed, but blue light is scattered and radiated, creating the blue sky you see every day. That blue light is not as visible from space, but plays a role in the blue color of the Earth. At night, the sunlight no longer is around to interact with the gases, so the sky become black.

Water Coverage

The Earth has many oceans and seas, from the Arctic Ocean to the Southern Ocean. Although there is red-hot heat below the surface of the Earth, the top layer is dominated by water. The oceans cover about 71 percent of the Earth and are blue, while land makes up the other 29 percent and varies in color, from green to tan to white. This gives the Earth the appearance of a blue marble. If the planet consisted mainly of land masses, it would be appear to be a different color completely.

Water Color

Although water covers a large percentage of the Earth, it is important to understand why the water is blue as well. As with the Earth's atmosphere, most of the colors of the light spectrum are absorbed by the water. The water radiates the blue in the spectrum, giving it its blue color. If another color were radiated, say red for instance, the Earth would look red from outer space, like Mars. The land masses of the Earth do not look blue due to this same principle.

Some Contradictions

The Earth only appears blue if you are looking at it from outer space on the side that is being lit by the sun. When you are orbiting the Earth, it will appear black when you orbit around a part of the Earth that is experiencing night. Because there is no sun to create the light, all of the Earth will appear somewhat dark. The stars will be more visible as well during this period. Land masses will appear somewhat dark blue, as there are artificial light sources that illuminate the sky on land.

Credit: Sciencing

Picture credit: Google

Yes, Earth spins around a line between the poles called its axis. The axis is tilted over at 23.5° in relation to the Sun. Earth rotates once every 23 hours, 56 minutes and 4.09 seconds. The Sun thus appears to come back to the same place in the sky once every 24 hours.

Earth’s spin, tilt, and orbit affect the amount of solar energy received by any particular region of the globe, depending on latitude, time of day, and time of year. Small changes in the angle of Earth’s tilt and the shape of its orbit around the Sun cause changes in climate over a span of 10,000 to 100,000 years, and are not causing climate change today.

Daily changes in light and temperature are caused by the rotation of the Earth, and seasonal changes are caused by the tilt of the Earth. As the Earth orbits the Sun, the Earth is pulled by the gravitational forces of the Sun, Moon, and large planets in the solar system, primarily Jupiter and Saturn. Over long periods of time, the gravitational pull of other members of our solar system slowly change Earth’s spin, tilt, and orbit. Over approximately 100,000 – 400,000 years, gravitational forces slowly change Earth’s orbit between more circular and elliptical shapes. Over 19,000 – 24,000 years, the direction of Earth’s tilt shifts (spins). Additionally, how much Earth’s axis is tilted towards or away from the Sun changes through time, over approximately 41,000 year cycles. Small changes in Earth’s spin, tilt, and orbit over these long periods of time can change the amount of sunlight received (and therefore absorbed and re-radiated) by different parts of the Earth. Over 10s to 100s of thousands of years, these small changes in the position of the Earth in relationship to the Sun can change the amount of solar radiation, also known as insolation, received by different parts of the Earth. In turn, changes in insolation over these long periods of time can change regional climates and the length and intensity of the seasons. The Earth’s spin, tilt, and orbit continue to change today, but do not explain the current rapid climate change.

credit: UNDERSTANDING GLOBAL CHANGE

Picture credit: Google