Module #3 - Earth Within a System and Effects of Our Moon


1. Part 1: Content and General InformationRead the content below about the Earth within a System. Watch all related videos (and add to your Video Journal submissions) and go to all related websites for reference. Make detailed notes in your "Virtual or actual Notebook" - DO NOT SIMPLY CUT & PASTE INFORMATION into your notebook, instead make point-form notes that you can read and refer to when studying for the Unit Test or Exam. 

2. Complete Quiz #1: Introduction to Planetary Systems (located on the D2L) of the course after you have completed completed Part 1: Content and General Information and submit your answers to Mr. Durk via the UGDSB D2L (20 marks). You will only have access to this quiz from 11:15 - 11:45 a.m. today. Good luck! Your mark for Module #3 is solely based on your performance on this quiz. 

3. Watch the Video of the Day:  Video: The Birth of Our Moon (24 min.) and make point-form notes in your Video Journal (on Google Docs) before you start today's lesson.

YouTube Video

Earth Within a System

Please remember to record all definitions and content in your digital notebook (using google docs). Links to WIKIPEDIA articles can be found by clicking on highlighted words in RED. Hyperlinks to other external websites are highlighted in BLUE.

Although we can’t be certain of how Earth was formed, certain hypotheses have been developed by scientists based on their observation of our solar system and its various components such as the other planets, moons and the asteroid belt to name only a few.


Image of Large Accretion Disk
(Credit: Michael Owen, John Blondin (North Carolina State Univ. )NASA


Accretion is one hypothesis based on the process of growth through accumulation. Meteorites and planetesimals colliding with Earth added to its mass. The larger mass increased its gravitational pull attracting larger meteorites. The materials which fell were mainly oxides of silicon, iron and magnesium. Metallic iron containing small amounts of radio active material also fell. This process is still happening today as meteorites fall to the earth from space.


Differentiation is a process by which the denser portions of a planet will sink to the center while less dense materials rise to the surface. Such a process tends to create a corecrust, and mantle. The melting of the earth’s interior was a result of the accumulated heat of gravitational energy (things falling to the earth) and due to heat from the decay of radioactive isotopes of elements such as uranium, thorium and potassium. Once the earth’s interior melted, heavier elements of iron and nickel were attracted inward, while the lighter elements of silicon, magnesium, and aluminum moved outward to make up the mantle and crust of the planet. This process is still happening today, as plates melt - elements separate. Differentiation of this type, creating layers in the earth, could only have happened if the planet was in a liquid or semi-liquid state.

Movements of the earth:

The three basic movements that produce day and night, the terrestrial year, and the seasons are:

RotationThe earth rotates on its axis once every 24 hours. This rotation allows the excess radiation built up during the day to escape into outer space at night. Without such a rotation the daylight side of the globe would be impossibly hot and the night time side impossible cold.

Wobble: The earth wobbles on its axis every 40 000 years (approximately). The axis of the earth is at a 23.5 degree(average) tilt of 23.5 degrees from vertical and moves in and out of this wobble between 21.5 and 24.5 degrees every 40 000 years or so.

Revolution:The earth revolves around the sun once every 365.25 days. Since the terrestrial year is only 365 days, every 4th year an extra day is added to gain back the lost time (Feb 29th).


 The Moon


Although there are a few theories about the origin of the moon, the collision ejection theory is the most probable. This theory suggests that the moon formed when a large asteroid collided with the earth about 4.6 billion years ago, ejecting molten debris into space, which eventually cooled and formed the moon. Although we will never know for certain the exact origin of the moon, supercomputer simulations of a collision and the density and composition of lunar rock support this theory, making it the most widely accepted.

Video: Origin of Our Moon (10 min.) (please make point form notes in your Video Journal)


The moon’s diameter is about a quarter the size of Earth’s and has a mass about 80 times less. The moon completes one orbit of the earth every 29.3 days (lunar cycle) (time for the moon to go through a complete set of phases), is 29.5 days. Interestingly enough, the moon has a synchronous orbit, revolving once on its own axis in the same amount of time it takes to orbit the earth, so that we always see the same “face” of the moon. Why does this happen? This occurs because the earth exerts tidal forces on the moon, causing its near side to be held in place facing the earth.

Phases of the Moon:

By observing the moon over a period of several weeks, one will notice that the moon rises and sets at different times each night, and that there is a regular progression through lunar phases. In a month, the moon progresses through one lunar cycle and will vary between being a completely dark new moon and a fully illuminated full moon. The lunar phases are caused because the orbit of the moon around the earth will vary the moon’s position in relation to the sun. Half of the moon is always lit by the sun, but the portion that we see will change depending on where the moon is in its orbit. During new moon, the moon rises and sets at the same time as the sun, and is therefore in the sky during the day. During a full moon, the moon is opposite the sun and is fully lit. The moon rises at sunset and sets at sunrise when it is full, so the moon is always visible in the night sky while full.

Link: Phases of the Moon Explained

Link: Moon Phases Calendar

The saying “Once in a blue moon” is a referral to when two full moons occur in the same calendar month.

Acknowledgements: Canadian Space Agency.


Please remember to record all definitions and content in your virtual notebook. Definitions can be found by clicking on highlighted words.


The earth’s axis of rotation is tilted at an angle of 23.5 degrees from the orbital plane while we circle the sun. Because of this tilt, the ecliptic and the celestial equator are inclined 23.5 degrees from each other. The progression of the sun along the ecliptic will cause it to be located north of the celestial equator for half the year and south for the other half of the year. The Northern Hemisphere experiences the warm temperatures of summer while the sun is north of the celestial equator. This is because the Northern Hemisphere is tilted towards the sun at this time, and as a result is exposed to the sun’s light for a longer period of time over one complete axial rotation (one day) during the summer. This leads to earlier sunrises and later sunsets, and because the sun is in the sky for a longer period of time, we receive more heat from the sun over the course of a day in the summer. The 23.5 degree tilt also causes the sun to follow a higher path in the sky, resulting in the Northern Hemisphere receiving more direct sunlight and therefore providing the warmer temperatures.

Summer solstice

The point along the ecliptic when the Sun is furthest north of the celestial equator (at its highest point in the sky) is called the summer solstice (usually 21 June) and is the longest day of the year in the northern hemisphere. Winter in the northern hemisphere occurs for the exact opposite reason: the Sun is south of the celestial equator and as a result the days are shorter in duration and less energy is received because the Sun is far lower in the sky.

Winter Solstice

The winter solstice (usually December 21) occurs when the sun is furthest south of the ecliptic. It should be noted that when it is winter in the Northern Hemisphere, it is summer in the Southern Hemisphere with longer days of more direct sunlight. In addition to the solstices, which officially mark the first days of summer and winter, there are also two equinoxes. These are the two points where the ecliptic crosses the celestial equator.

Vernal Equinox

The vernal equinox officially marks the first day of spring in the Northern Hemisphere (autumn in the south) and is when the sun crosses the celestial equator moving north.

Autumnal equinox

The autumnal equinox occurs when the sun crosses the same plane traveling south, and is officially the first day of autumn (spring in the south). On these two days, the sun is in the sky for 12 hours; these are the only days of the year where day and night are of equal duration.

Video: Why Does the Earth Have Seasons? (20 minutes)  (please make point form notes in your Video Journal)

YouTube Video

For an animated model of Earth’s orbit around the sun, refer to this link.

Earth, Sun, Moon: Tides and Eclipses


To view an animation of an eclipse, refer to this link.

During the moon’s orbit around the earth, it will occasionally pass through the earth’s shadow, or will cast its shadow on the earth. These events are known as lunar eclipses and solar eclipses, respectively.

Lunar eclipses:

Lunar eclipses occur when the moon passes through the earth’s shadow. Because the moon has to be on the opposite side of the sky from the sun for this to occur, a lunar eclipse can only take place during the full moon phase. During a lunar eclipse, the earth’s shadow will travel across the face of the moon, which will appear as though a bite has been taken from it. At total eclipse, the moon will not darken completely but instead glow deep red because the earth’s gravity will refract (bend) a small amount of light from the sun onto the lunar surface. Because the earth casts a relatively large shadow, lunar eclipses occur a couple of times a year and are visible to large regions on the earth, lasting up to 100 minutes.

Solar eclipses:

Although the frequency of solar eclipses is not considerably different from that of lunar eclipses, they are rarely seen because they are visible only along an extremely narrow path of the earth. During a solar eclipse, the moon obstructs the sun and casts its shadow on the earth. However, because the moon is relatively small, the shadow cast during totality never exceeds 270 kilometres in width. If the observer is located in only a portion of the shadow (the penumbra), she/he would observe a partial solar eclipse, where the moon would only partially cover the sun. Despite being partially obscured, the sun is still so bright it would appear no different to the unaided eye (Note: never look directly at the sun, even during a solar eclipse). It is not until the observer is located within the central region of the moon’s shadow (the umbra) that the sun becomes completely covered. Totality of a solar eclipse lasts at most about seven and a half minutes, at which time only the sun’s corona is visible and several stars will be visible in the daytime sky. Because a solar eclipse can only occur when the sun and moon are in the same region of the sky, it can only take place during the new moon phase.

To view an animation of an eclipse

Tides and Tidal Interaction:

For millions of people in the world living along the ocean, the daily fluctuations of the oceans’ water level are important factors of life. Tides occur because of the gravitational attraction between the earth, the sun and the moon. The sun and moon actually tug at the earth’s oceans, causing a tidal bulge (the tidal influence of the moon is about twice that of the sun). Each coastal location experiences approximately two high tides and two low tides each day; when it is high tide at one coastal location, it is low tide along a different coast a quarter of the way around the earth. Because tides occur due to the gravity of both the sun and moon, there are two different classifications of tides, which depend on the orientation of the sun and moon. A spring tide occurs when the sun, moon, and earth are all in a line (full or new moon), and causes the greatest tidal differences because the sun and moon act together to create one large tidal bulge. A neap tide, on the other hand, occurs near a quarter moon phase when the sun and moon are at right angles from each other, causing a smaller tidal bulge. In addition to the effect of the orientation of the sun and moon, the distance to the moon will also affect the tide levels. During perigee (when the moon is nearest to the earth), the gravitational pull of the moon is about 40% greater than if it were at apogee.

The world’s greatest tides occur right here in Canada, in the Bay of Fundy in Nova Scotia. The greatest variation occurs in Minas Basin, on the eastern extremity of the Bay of Fundy where, if the moon is near perigee during a spring tide, the water level can be as much as 16 metres higher at high tide than at low tide.
Try here for an interactive review of the content. (Please try this resource at home or on a chromebook)

Acknowledgements: Canadian Space Agency