the tilting of the earth

8/3/2019 The Tilting of the Earth

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By Eric McLamb, September 10, 2011

(http://www.ecology.com/2011/09/10/tilting-earth-shaping-seasons/)

In early January each year, Earth reaches its closest distance to sun. At this time, the northernhemisphere experiences winter while the southern hemisphere experiences summer. TheEarth travels to its farthest point from the sun at the beginning of July each year, when it issummer in the Northern Hemisphere and winter in the Southern Hemisphere.

Earth¶s Movements

Earth travels around the Sun at about 18.4 miles per second while rotating on its axis at about1,070 miles per hours. Pictured above is Earth during summer for the Northern Hemispherewhere the North Pole (center of the Arctic Ice Cap) receives sunlight 24 hours a day. Image:University of Toledo)

Hurtling through space at an average speed of 18.4 miles per second (30km per second),Earth is constantly changing its position with the sun. Not only is the Earth orbiting around thesun, but it also rotating on its axis at 1,070 miles per hour (1,722 km per hour), the speed atthe equator. It is, however, a common misconception that the Earth¶s distance from the sundetermines how warm or cold the planet gets.

While it is true that Earth does have a perihelion, or point at which it is closest to the sun, andan aphelion, its farthest point from the sun, the difference between these distances is toominimal as to have any significant impact on the Earth¶s seasons and climate. The average

Environmental Articles:The Tilting of the Earth: Shaping Our Seasons and

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distance of the Earth from the sun is about 93 million miles (149.6 million km) also referred toas one astronomical unit or AU. At its closest point, the Earth is about 91.1 million miles (147million km) from the sun; conversely, the sun is about 94.8 million miles (152 million km) awaywhen it is at aphelion. With these numbers, it¶s easy to figure out that the Earth¶s orbit aroundthe sun is not so much elliptical (oval) as it is circular, and that the Earth¶s distance from thesun remains relatively constant throughout its annual orbit.

So what does the Earth¶s orbit around the sun have to do with our planet¶s constantly changingtemperatures and changing seasons? The answer is« everything! The Earth is constantlychanging its position with the sun. That¶s because the Earth tilts in relation to the sun. That iswhat creates the differences in the seasons and the annual warming and cooling cycles of theEarth¶s Northern and Southern Hemispheres.

The Earth is tilted 23.5 degrees on its axis, a straight line through the planet from the NorthPole to the South Pole. The Earth spins around, or rotates, on this axis as it orbits the sun. Thekey here is that as the Earth orbits the sun, different regions on Earth tilt both towards andaway from the sun, depending on the region¶s respective hemisphere. This causes the sun¶slight and energy to hit the different regions of the Earth at different angles throughout the

course of one orbit, or one full year.

The Seasons

This diagram indicates the orbital position of the Earth as it reaches winter, spring, summer and fall. Note the tilt in relation to the Sun. Source: NOAA

When the North Pole tilts most toward the sun, the Northern Hemisphere experiences summer.This occurs when the Earth is farthest away from the sun, and begins around June 21-22.

Astronomers refer to the arrival of this event as the Summer Solstice in the NorthernHemisphere. This is the time when Earth reaches its closest orbital distance to the sun. As theEarth continues along its path around the sun, its angle constantly shifts the North Pole away



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from the sun and the South Pole toward the sun. The sun¶s energy is more concentrated onthe Northern Hemisphere where its rays hit the Earth more directly and are thus more intense.

At the same time, however, the Southern Hemisphere tilts away from the sun, causing thesun¶s rays to hit the region more at an angle and with less intensity. This brings about winter inthe Southern Hemisphere, called the Winter Solstice.

The Equinoxes

Spring and Fall (or Autumn) occur midway on the Earth¶s journey from winter to summer andfrom summer to winter. These times occur when the sun appears to be directly over theEarth¶s equator, and the length of days and nights are equal over most of the planet. On March20 or 21 of each year, the Earth reaches the vernal equinox, which marks the arrival of Springin the north and Fall in the south. The autumnal equinox occurs on September 22-23 andmarks the arrival of Fall in the north and Spring in the south.

Putting It All Together

Venus' surface (pictured) maintains an average temperature of about 882°F due to theextremely high concentrations of carbon dioxide (CO2) in its atmosphere. CO2 is agreenhouse gas that also exists in Earth's atmosphere but at lower concentration levels thathelp maintain life-sustaining temperatures. Source: NASA

We know that Earth rotates on its axis as it travels around the sun in an almost circular orbit.We also know that, because the Earth tilts on its axis, its seasons change as it orbits the sun.When it is Summer in the Northern Hemisphere, it is Winter in the Southern Hemisphere, andthis has nothing to do with how close or far the Earth gets to or away from the Sun in its orbit.It¶s all because the Earth is tilted on its axis.

The Earth¶s overall orbit or distance from the sun would make a difference if it was locatedwhere, for instance, Mercury is or where Pluto is. As Dr. Jack Hall from ecology.com¶s Dr.Jack¶s Natural World says: ³It¶s the three bears syndrome. We¶re not too close to the sun, andwe¶re not too far away. We¶re j-u-u-u-u-st right!)



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All this does not explain why our planet maintains its relatively warm, life-sustainingtemperatures and climates that can ² for the most part ² sustain life. It also does not explainwhy life on Earth doesn¶t burn up. For Earth to maintain its average temperature of 61°F(16.1°C), it requires a very delicate balance within its atmosphere, oceans and solid Earth.

The Sahara Desert, pictured, records the hottest temperatures on Earth. Located in thenorthern part of Africa, the Sahara's highest temperatures average around 130°F. Image: MITEarth¶s coldest temperature averages about minus 60°F (-45°F to -97°F) and its hottesttemperature averages about 130°F-plus. While these extremes make most life impossible tonaturally exist or thrive, they occur only in remote areas of the planet, such as the Antarctic(coldest average temperatures) or the Sahara Desert (hottest). Still, these temperatures arerelatively warm (or cool) compared to other planets.

Earth¶s ³Checks and Balances´

Earth has a built-in, naturally-occurring ³force field´ around it that creates and helps maintainviable living conditions for its plant and animal inhabitants. The atmosphere containsgreenhouse gases like carbon dioxide to keep the Earth warm, and an ozone layer to protectthe Earth from harmful and incinerating (burning) radiation.

The Earth also has other checks and balances that help it absorb and retain the sun¶s heat andenergy (such as the oceans) as well as reflect its energy back into space (such as the polar icecaps). Wind and ocean currents also help distribute this heat around the globe, all within theEarth¶s protective atmosphere. The point is that Earth is unique in its ability to create andmaintain sustainable living conditions, because all of its systems and influences are connectedto each other, from its atmosphere, oceans and land, to its seasons, its living inhabitants andthe sun.



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Did you know«.?

y The hottest temperature ever recorded on Earth is 136°F in El Azizia, Libya, in Northern Africa on the northern fringe of the Sahara Desert. A close second is Death Valley inCalifornia¶s Mojave Desert, which registered 134°F on July 10, 1913.

y The coldest temperature ever recorded on the planet¶s surface did not occur at theSouth Pole but at Vostok, Antarctica, on July 31, 1983. It was -128.6°F

y It is the Sahara Desert¶s dryness, not heat, that makes it a desert. The frozen continentof Antarctica, the coldest place on Earth, is so dry that some scientists consider it adesert, too.

y Our solar system orbits around the center of the Milky Way, our home galaxy. It takesapproximately 225 million years for the sun to make one revolution or trip around theMilky Way.

y The speed of the Earth is fastest when it is closest to the Sun, in January, and slowestwhen it is farthest away from the sun, in July. In other words, in January, it will bemoving faster than average, and in July, it will be moving slower than average.

y Earth¶s solar system is located on the outer edge on the Milky Way, about 28,000 lightyears from the center of the galaxy. Most of the Milky Way¶s 200 billion other stars andtheir planets are clustered in the center. This leads many scientists to believe that if thesolar system were located more toward the center of our giant galaxy, life on Earthwould be impossible because of the overwhelming heat and energy emitting from thosestars.

y Although most planets spin on their axis that are tilted only a few degrees, the thirdlargest planet, Uranus, spins on an axis that is virtually perpendicular to the sun. Still, itis hotter at its equator than at its poles, the reasons for which are unknown.



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Questions on the Article

DIRECTIONS: After you read the article, answer the questions below. Questions with a *before them are questions that ask you to think about what you have read and do notalways have answers right from the text.

1. What happens in January in terms of how close the earth is to the sun? Whathappens in July? What is different about the northern and southern hemisphere thistime of year?

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2. How fast does the earth move around the sun? How fast does the earth spin on itsaxis?

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3. *Why do you think the spin of the earth does not seem so fast to us?

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4. What is the difference between perihelion and aphelion? Why doesn¶t the differencebetween these two points affect the seasons that much?

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5. What actually creates the changes in temperature and season?

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Environmental Articles:The Tilting of the Earth: Shaping Our Seasons and

Climates



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6. What is the earth¶s axis? What is the angle at which the earth is tilted on its axis?

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7. At the time that summer occurs in the Northern Hemisphere, the earth is actually thefarthest distance from the sun. What fact makes summer happen at that time?

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8. *What is happening to the angle of the sun¶s rays during winter? What is happeningto the angle during summer? Why does this make a change in season andtemperature?

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9. What is the vernal equinox? What is the autumnal equinox? What do these twoevents have in common?

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10. What is the surface temperature of the planet Venus? Why is it so warm?

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11. What is in our atmosphere that helps maintain conditions that are life-sustaining? *What would happen if the amount of this substance would increase a lot? Why is earthsubject to the ³three bears syndrome´?

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12. What is required to maintain the earth at an average temperature of 61°F?

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13. What two places on earth have the most extreme hot and cold temperatures?

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14. What are the earth¶s two main checks and balances?

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15. List the other check and balances mentioned in the article:

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Write down the article¶s main idea in a short sentence:

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the tilting of the earth

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