Many people have serious misconceptions about the causes of phenomena such as seasons, lunar phases, tides, eclipses ,not to mention the processes that formed our Earth all those billions of years ago. In this unit, we will attempt to alleviate these misconceptions.

Scientists estimate the age of the Earth to be approximately 4.6 billion years. The Earth is not static, but still evolving… changing. The processes that shape the Earth still confusing to many people.

This is a solar nebula…a nursery in space. Our solar system formed much like this one. A collapsing interstellar cloud caused by a nearby supernova provided the space “debris” needed for the construction of our solar system.

The hottest densest materials clumped together in the center.

This hot dense area formed our Sun, and the inner planets, which in the beginning were so hot they were molten.

As time passed (billions of years), these inner planets hardened into the “terrestrial” planets they now are. These terrestrial planets are:

Mercury

Venus

Earth

Mars

The outer planets are frozen gases, and are able to exist because of their great distance from the sun. They are sometimes called the Jovian planets. They include:

Jupiter

Saturn

Uranus

Neptune

In this, the Orion Nebula, you can see evidence of the protoplanets called “Planetesimals” forming through “accretion”. Accretion is a “clumping together” of solid objects.

The rings, and large number of natural satellites (moons) on these outer planets, are similar to miniature solar systems themselves. As the sun formed, a huge stellar wind blew a band of meteorites between Mars and Jupiter, which is thought to be left over from this early stage of development.

By studying the band of meteorites between the planets Mars, and Jupiter, scientists have found that the solar system is about 4.6 billion years old! They are materials from the beginnings of our solar system that have changed relatively little since their original formation as rocks. Geologists use radiometric dating methods to determine the ages of these “rocks”, many of which have bombarded the Earth through the eons.

We are lucky that we formed where we formed, because Earth is the only planet in the solar system that can sustain liquid water, and temperate climates, two necessities for life, as we know it.

The moon is immensely important to the Earth, and the life on it. It is the second brightest object in our sky after the sun, being only 238,850 miles from the Earth. This brightness, of course, comes from the reflection of sunlight, as the moon produces no light of its own.

The moon completes its orbit of the Earth in one month, and interestingly enough, rotates on its axis at the same rate. This is a phenomena known as synchronous rotation. Were it not for the first lunar

probes which mapped and photographed the dark side, we would still be unaware of what it looks like.Go to this website, and play for awhile. Check out how the image of the Earth changes from perspective.

http://www.fourmilab.ch/cgi-bin/Earth

As our day lengthens due to rotation slowing, (which is actually happening), the lunar cycle will change.

It has been calculated that in one billion years, the length of an Earth day will be about 1080 hours. That is 45 days now!

Why would a knowledge of Earth-Sun-Moon cycles be important for you to know about?

How do these cycles affect ecosystem?

For homework tonight, determine what stage the moon is in now, and be ready to reflect on it on Wednesday!

Life is a result of the tidal forces of the Moon. Isaac Asimov wrote in his "Tragedy of the Moon" 1972, that life evolved in the sea did not want to move to land. There was no reason to, no movements to force the life forms to the surface. One look at tide pools and one can understand the purpose of this statement - that we do life in a unique environment:Earth would spin much faster without its orbiting moon. That's because the moon's gravity pulls on Earth's oceans. The moon is largely responsible for the tides. The pull of the moon, and ebb and flow of the tides, puts the brakes on Earth's daily rotation.

The Moon has been a stabilizing factor for the axis of rotation of the Earth. For this reason, we had much less climatic change than if the Earth had been alone.

The diagram below should help you visualize the seasons. The seasons of which hemisphere are being documented? How do you know? What would happen if there were no tilt to the axis? Visualize it!

1. The northern hemisphere is being documented, because on Summer Solstice, the NH is tilted towards the sun, and the SH is pointed away. It would be Winter Solstice in the SH.

2. No tilt, means no seasons. Eternal Spring/Autumn!

As you can see, at summer solstice in the NH (June 21), the most direct rays of the sun are striking the Earth at the Tropic of Cancer. This is the farthest north the direct rays of the sun are going to ever reach, and that is because of the tilt of the Earth’s axis.

On June 22, the direct rays of the sun begin migrating south, where they will be directly over the equator on what day?

ANS: Autumnal EquinoxThe determination of whether it is winter, or summer

solstice is defined by the hemisphere you are describing.

The Summer Solstice in the SH (Dec 21) means the most direct rays of the sun are reaching the Tropic of Capricorn, 23.5° S latitude. They will never go farther south than that, because of the angle of the Earth’s tilt.

On December 22, the sun’s rays will begin again moving northward toward the equator, where they will be most direct on what day?

ANS: Vernal Equinox

As you can see, this is summer solstice for the SH. It is winter solstice for the NH.

As you can see, on the equinoxes, the direct rays of the Sun are striking the equator, and every location on Earth is receiving equal day, and equal night.

How many daylight hours will Vostok Antarctica be receiving on the Equinox?

ANS: 12

How many nighttime hours will the North Pole be receiving on the Equinox?

ANS: 12 Without meaning to, this diagram may seem confusing, because it appears that the Earth is not tilted 23.5°. It most certainly is tilted, however the tilt is not a factor during the equinoxes, as this diagram shows. http://esminfo.prenhall.com/science/geoani

mations/animations/01_EarthSun_E2.html

When determining proximity to the sun, the Earth is closest at or around Jan 3, and this is known as Perihelion. (91,402,505 miles)

We are farthest from the sun at or around July 4, and this is known as Aphelion. (94,509,130 miles)Does aphelion, or perihelion impact our seasons at all on Earth?

No, not in the slightest!

A solar eclipse occurs when the occasional path of the moon obliterates the path of the sun in our daytime sky. A total solar eclipse is a relatively rare event, while a partial solar eclipse is relatively common. Since the angle at which the moon moves above the horizon is different, depending upon your vantage point on Earth, total and partial solar eclipses are not visible everywhere on Earth at the same time. You may have been

taught as a child that the only safe way to view a solar eclipse (except when the solar corona is apparent), is with a pinhole camera. We have the fortune of having many websites and NASA to help us with photographs as well.

Unlike the solar eclipse, the lunar eclipse occurs when the Earth casts its shadow on the moon (instead of the other way around).

The night of a lunar eclipse, there is always a full moon.

As you can see, during a lunar eclipse, the moon takes on a shadowy appearance as the Earth passes between it, and the sun. It is not totally hidden in Earth’s shadow, but has an eerie orange hazy color.

Lunar eclipses can be viewed to some extent everywhere from the dark side of the Earth. Some are partial, some are total (as seen above)

The Earth’s climate has changed much over the course of history. Climate change can occur from natural causes, such as from the sun’s intensity, changes in Earth’s orbital pattern around the sun and natural processes within the climate system. (like what?)              More recent impacts on climate change have been human induced. Humans are influencing climate through deforestation, reforestation, desertification and urbanization.

Manmade changes in the atmosphere’s composition by the burning of fossil fuels like coal and oil have trapped greenhouse gases, causing temperatures to increase recently.

Earth’s average surface temperature has increased from 1.2 to 1.4 degrees Fahrenheit since 1900. This may not sound like much, but it’s enough to create changes in rainfall patterns, snow, ice covers, and sea levels.

These human-induced greenhouse gases are detrimental to our environment as they prevent heat from escaping into space. As the concentrations of these gases accumulate in the atmosphere, the Earth’s temperature rises.

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