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Explanation of characteristics of the Earth to Succeed in Physical Science. Also refer to physics, planet, moon, orbit, Sun, Moon, axis, tilt, revolving, seasons, daylight, seasons, gravity, magnetism, force fields, characteristics, composition, escape velocity, Ron Kurtus, School for Champions. Copyright © Restrictions Characteristics of the Earthby Ron Kurtus (revised 19 October 2004) Our planet Earth is a rotating sphere that orbits the Sun. The Earth's axis of rotation is at a constant tilt with respect to its orbit around the Sun, resulting the change of seasons. The physical characteristics of the Earth include its size and composition. The Earth also has gravity and magnetic force fields. Questions you may have include:
This lesson will answer those questions. There is a mini-quiz near the end of the lesson. Useful tools: Metric-English Conversion | Scientific Calculator.
Time = 7 min. 51 sec. Earth's relationship with SunThe Earth is the third planet from the Sun, with Mercury and Venus being closer. Its unique position gives the Earth a temperate climate, allowing the chemical reactions necessary to sustain life. But over the years, the climate has varied enough to melt the ice caps near the North and South poles, or to cause glaciers to move south in an Ice Age. Rotates in an orbitThe Earth goes around the Sun in an orbit, taking a year or about 365 days to make one revolution. The orbit is an ellipse, so the Sun is off-center.
The Earth orbits the Sun The average distance from the Sun is 149,597,890 kilometers (92,955,820 miles). This distance is so great that it takes light about 8 minutes to reach the Earth from the Sun. Spins on its axisThe Earth spins on its axis, making one revolution in 24 hours. The spinning of the Earth on its axis is what causes the Sun to appear to move across the sky. The effect the apparent movement of the Sun is similar to looking out the window of a moving car, where things outside appear to be moving past you. Tilt affects seasonsThe Earth's axis also tilts with respect to the Sun, causing the changes of the seasons. In summer, the Earth is tilted such that the Sun falls more directly, while in winter the Sun looks lower in the horizon and the light comes at a glancing angle. The tilt of the Earth also causes the summer days to be longer than the nights. In winter the days are shorter and there is less light to heat the ground.
The light from the Sun is more direct in summer than The further north you go, the more the effect of the tilt is of the Earth is apparent. Above the Arctic Circle, daylight is can be seen for a full 24 hours in the summer or night can be 24 hours in the winter. That is why they call the area "the land of the midnight sun." (See Motion of the Earth for more information.) MoonThe Earth has only one moon, while Mars has two moons and Jupiter has 9 moons. (See The Moon for more information.) Physical characteristics of EarthPhysical characteristics include shape, size and composition. Spherical in shapeJust as the Sun and Moon appear as spheres, so too is the Earth spherical in shape. To people on Earth, the planet appears to be generally flat (not counting for hills and valleys), but in reality the surface of the Earth has a slight curve. This can be noticed when looking out on a large lake or the ocean and seeing a ship come up along the horizon.
Ship coming up over the horizon The shape of the Earth has been proven by ships circling the Earth, as well as from pictures of the Earth taken from the space vehicles.
View of Earth from space Its shape is actually slightly flattened at the poles. SizeThe diameter of the Earth at the equator is 12,756 km (7,926 miles), and its circumference or distance around the Earth at the equator is 40,075 km (24,901 miles). CompositionThe composition of the Earth consists of the solid and liquid portion and the atmosphere or gaseous portion. Solid and liquidThe percentage composition of the Earth's solid and liquid materials (by mass) is:
Oxygen is chemically combined with many substances to produce liquid and solid compounds. Although water (H2O) is a dominant compound on Earth, Hydrogen is not listed above because of its small mass. Silicon Dioxide (SiO2) is sand, and that compound makes up a large portion of the Earth's mass. Much of the Iron is in the Earth's core and is responsible for the Earth's magnetic field. AtmosphereAlthough most people think air is mainly Oxygen, the atmosphere of the Earth actually consists of 79% Nitrogen (N2), 20% Oxygen (O2) and 1% of other gases such as Carbon Dioxide (CO2). Force fieldsThe Earth has two major force fields: gravity and magnetism. GravityGravity is the force at a distance that attracts objects of mass toward each other. The force of gravity from the Earth holds down our atmosphere, oceans and everything else. Lost atmosphereSome planets and moons that have less gravity than Earth have lost their atmosphere because it wasn't sufficient to hold the gas close to the surface. Escape velocityWhen you throw a ball or shoot a bullet upward, it will slow down due to the Earth's gravity, until it finally falls back to the ground. You would have to shoot the object at 40,248 km/hr (25,009 mph) for it to escape the Earth's gravity and fly out into space. This is called the Earth's Escape Velocity. (See Gravity for more information.) Magnetic fieldThe Earth is like a giant magnet with a magnetic pole near the North Pole and the opposite near the South Pole. The north pole of a magnet seeks the North Magnetic Pole. Through the ages, indications are that the poles switched directions. No one is sure why this happened. The rotation of the Earth and the fact that the core of the Earth is made of iron are major factors in creating the magnetic field. One thing the magnetic field does is to attract charged particles that have been emitted from the Sun. The focusing of these particles at the poles may help to prevent us from being harmed by the high energy particles. These particles cause the air in the upper atmosphere to glow. This is called the northern lights (aurora borealis) or southern lights (aurora australis). (See Magnetism for more information.) SummaryThe Earth is a sphere that rotates and tilts, causing the effect of days and seasons. It also revolves around the sun in our solar system. It is the third planet from the Sun and possesses a magnetic field. This is the only Earth we have. Keep it a good place to live. ResourcesThe following resources provide information on this subject: WebsitesEarth Facts and Figures - From NASA The Earth - Details from Nine-Planets website Earth's Atmosphere - From the University of Tennessee Department of Physics Space Weather - News about Earth-Sun environment Earth's Magnetic Field Is Fading by John Roach for National Geographic News September 9, 2004 Books on the Earth
Top-rated books on Earth Astronomy MiscellaneousMini-quiz to check your understanding1. What does the Earth's unique position with the Sun allow? 2. Is the Earth an exact sphere? 3. What does the rotation of the Earth help create? If you got all three correct, you are on your way to becoming a Champion in Physical Science. If you had problems, you had better look over the material again. What do you think?Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. We will try to get back to you as soon as possible. Share linkFeel free to establish a link from your website to pages in this site. 
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