Astronomy

Exploring the Planet Earth. Earth and its Moon - From the perspective we get on Earth, our planet appears to be big and sturdy with an endless ocean of air. From space, astronauts often get the impression that the Earth is small with a thin, fragile layer of atmosphere. For a space traveler, the distinguishing Earth features are the blue waters, brown and green land masses and white clouds set against a black background.

Many dream of traveling in space and viewing the wonders of the universe. In reality all of us are space travelers. Our spaceship is the planet Earth, traveling at the speed of 108,000 kilometers an hour.

Earth is the 3rd planet from the Sun at a distance of about 150 million kilometers. It takes 365.256 days for the Earth to travel around the Sun and 23.9345 hours for the Earth rotate a complete revolution. It has a diameter of 12,756 kilometers, only a few hundred kilometers larger than that of Venus. Our atmosphere is composed of 78 percent nitrogen, 21 percent oxygen and 1 percent other constituents.

Earth is the only planet in the solar system known to harbor life. Our planet’s rapid spin and molten nickel-iron core give rise to an extensive magnetic field, which, along with the atmosphere, shields us from nearly all of the harmful radiation coming from the Sun and other stars. Earth’s atmosphere protects us from meteors, most of which burn up before they can strike the surface.

From our journeys into space, we have learned much about our home planet. The first American satellite, Explorer 1, discovered an intense radiation zone, now called the Van Allen radiation belts. This layer is formed from rapidly moving charged particles that are trapped by the Earth’s magnetic field in a doughnut-shaped region surrounding the equator. Other findings from satellites show that our planet’s magnetic field is distorted into a tear-drop shape by the solar wind. We also now know that our wispy upper atmosphere, once believed calm and uneventful, seethes with activity — swelling by day and contracting by night. Affected by changes in solar activity, the upper atmosphere contributes to weather and climate on Earth.

Besides affecting Earth’s weather, solar activity gives rise to a dramatic visual phenomenon in our atmosphere. When charged particles from the solar wind become trapped in Earth’s magnetic field, they collide with air molecules above our planet’s magnetic poles. These air molecules then begin to glow and are known as the auroras or the northern and southern lights.

Earth Statistics

Views of The Earth

The following set of images show some of the wonders of our planet.

South America

This color image of the Earth was obtained by Galileo at about 6:10 a.m. Pacific Standard Time on Dec. 11, 1990, when the spacecraft was about 2 million kilometers from the planet. Galileo was making the first of two Earth flybys on its way to Jupiter. South America is near the center of the picture, and the white, sunlit continent of Antarctica is below. Picturesque weather fronts are visible in the South Atlantic, lower right.

Africa

The crew of Apollo 17 took this photograph of Earth in December 1972 while the spacecraft was traveling between the Earth and the Moon. The orange-red deserts of Africa and Saudi Arabia stand in stark contrast to the deep blue of the oceans and the white of both clouds and snow-covered Antarctica.

Colored Infrared Earth Image

This infrared image of the Earth was taken by the GOES 6 satellite on September 21, 1986. A temperature threshold was used to isolate the clouds. The land and sea were separated and then the clouds, land and sea were separately colored and combined back together to produce this image.

Earth & Moon

Eight days after its encounter with the Earth, the Galileo spacecraft was able to look back and capture this view of the Moon in orbit about the Earth, taken from a distance of about 6.2 million kilometers, on December 16, 1990. The Moon is in the foreground, moving from left to right. The brightly colored Earth contrasts strongly with the Moon, which reflects only about one third as much sunlight as the Earth. Contrast and color have been computer enhanced for both objects to improve visibility. Antarctica is visible through the clouds (bottom). The Moon’s far side is seen; the shadowy indentation in the dawn terminator is the south Pole/Aitken Basin, one of the largest and oldest lunar impact features.

Antarctica

This image of Antarctica was taken by Galileo several hours after it flew close to the Earth on December 8, 1990. This is the first picture of the whole Antarctic continent taken nearly at once from space. Galileo was about 200,000 kilometers from Earth when the pictures were taken. The icy continent is surrounded by the dark blue of three oceans: the Pacific to the right, the Indian to the top, and a piece of the Atlantic to the lower left. Nearly the entire continent was sunlit at this time of year, just two weeks before southern summer solstice. The arc of dark spots extending from near the South Pole (close to the center) toward the upper right is the Transantarctic Mountain Range. To the right of the mountains is the vast Ross Ice Shelf and the shelf’s sharp border with the dark waters of the Ross Sea. The thin blue line along the Earth’s limb marks our planet’s atmosphere.

Clementine Mission

This false-colored image was acquired during the Clementine mission. It shows airglow of the upper atmosphere as a thin blue line. The bright spot toward the bottom is an urban area.

Mosaic of the United States

This image is a mosaic of the United States prepared by using 16 images from the Advanced Very High Resolution Radiometer (AVHRR) sensors on the meteorological satellites NOAA-8 and NOAA-9. The images were acquired between May 24, 1984 and May 14, 1986. On false-color infrared mosaics, vegetation appears in various tones of red instead of green. The “redness” indicates vegetation density, type and whether growing on dry land or in a swamp (a mixture of reddish vegetation and dark blue surface water produces dark tones). Grasslands appear light red, deciduous trees and croplands appear red, and coniferous forests appear dark red or maroon. Desert areas appear white and urban areas (pavement and buildings) appear bluish green. Lakes, rivers and oceans appear in various shades of blue, dark blue for deep water and light blue for shallow or turbid water. Exposed bedrock generally appears as a dark bluish-green or other dark tone.

Map projected image of Earth (AVHRR)

This image is a Homolosine projection of the Earth prepared from Advanced Very High Resolution Radiometer (AVHRR) image data.