Topic 3: Earth’s Movement in the Solar System (New Syllabus)

Topic 3: Earth’s Movement in the Solar System (New Syllabus)

CHAPTER 3 – Movement of the earth in the solar system

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The earth is in motion all the time. One does not feel this motion because one moves with it, like all other planets, the earth has two motions known as: –

(a)  Rotation

(b)  Revolution

Rotation

Rotation is the spinning of a body on its axis.

Earth’s rotation:is a spinning of the earth on its axis.

Axis of the earth is an imaginary line joining the North and South poles through the centre

The earth axis is tilled making an angle of 23 from the perpendicular

The earth rotates on it axis in an anticlockwise direction from west to east through 360 in 24 hours.

This means that the earth takes 1 hour to rotate through 15ᵒwhich is equal to 4 minutes for every 1ᵒ

The earth rotation changes from no movement at the poles to very fast movement at the equator

At the equator every point of the earth surface moves eastwards at about 1600km/hr. We do not feel the movement because we move with the earth movement at a constant speed. At latitude 40ᵒ the speed is about 1280km/hr. in the mean time at the poles the speed is 0km/hr.

Evidence to prove that the earth rotates;

1. Day and night
2. sun rise and sun set
3. Shape of the earth
4. Star trails
5. Time zones
6. Coriolis effect

A] Day and night: as the earth rotates on its aix, different parts of the planets faces the sun at different time.

B] Sunrise and sun set: the sun apperars to rise from east and set to the west.

C] Shape of the earth: the earth is not parfect square, it is flattened at the poles due to the absence of centrifugal force and strong gravitational pull. Mean while it burges at the equator because of strong centrifugal forces and weaker gravitational pull. All this are caused by unequal rotation speed at the poles and at the equator.

D] Star trails: when you look at the night sky stars appear to make a circular movement around the north or south poles from east to west. Infact the star do not move, this is bacuse the eath is rotating on its axis fro west to east.

E] Time zone: the division of earth into different time zones (24hrs) is based on the earth rotation. A as the earth spin on its axis, different regions experience daylight and darkness at different times.

F] Coriolis effect: this causes moving objects like winds and ocen currents to curve or be deflected due to the earths rotation. This effect influences the direction of wind patterns and ocean currents. The wind and ocean currents in the northern hemisphere are deflected to the rigt while in the southern hemisphere are diflected to the left.

Effect of earth rotation.

1. Day and night
2. Differences in time
3. Gain or loss of a day
4. Tides:
5. Deflection of winds and ocean currents:

A] Day and night: changes of day and night is caused by the rotation of the earth on its axis. The side that faces the sun will be expecting day light while the side that is not facing the sun at that time will be in darkness.

B] Different in time: the rotation of the earth causes differences in time in places located at different longitudes.As the earth rotates on its axis different places of the world experience daylight and darkness at different times.

C] Gain or loss of a day: this is related to crossing the internatinal date line, one will lose a day when crossing the internatinal date line(IDL) from the east and will gain a day when crossing the (IDL) from the west to the east. If the earth would not be rotating, there Would be neither gaining nor losing a day while crossing the (IDL)

D] Deflection of winds and ocean currents: the rotation of the earth causes deflection of planetary winds and ocean currents. This means they do not blow and flow straight. The planetary winds and ocean currents are defelected to the right in the northern hemisphere and the left in the suthern hemisphere.

This is based on ferrels law, which states that”freely moving bodies are deflected to their right in the northern hemisphere and to their left in the southrern hemisphere from their point of origin.

E] Tides: is a rising and falling of water level in ocean. This is caused by gravitational atraction exerted largely by the moon and partly by the sun upon the rotating earth. When the earth, the moon and the sun are in a straight line ocean water level rises and when the earth, the moon and the sun are not in a straight line, the ocean water level falls.

Revolution of the earth

Revolution is the movement of one body around another.

Earth’s revolution: is the movement of the earth around the sun

The earth takes 365 ¼ days for a complete revolution

When the earth takes 366 days to accomplish one revolution is called a  Leap year. However a normal year has 365 days

The fraction days are not counted every year, but they are added once in 4 year to make a leap year of 366 days.

The leap year occurs ones in every four years when the month of February has 29 days instead of 28..

Aphelion  and perihelion

Due to the shape of the earth’s orbit, the earth is very closer to the sun at one point of the year than at another

Aphelion is the furthest position of the earth’s orbit from the sun.

The earth is at Aphelion each year on 4th July  when it is in 152 million kilometers from the sun.

Perihelion is the nearest position of the earth from the sun.

The earth is at perihelion each year on 3rd January when it is 147.3 million kilometers from the sun.

Therefore the speed of revolution is about 29.66 km per second.

Effect of earth revolution

1. Season of the year
2. Varying length of day and night at different times of the year
3. Changes of Over Head Sun
4. Aphelion and perihelion
5. Eclipse.

Season of the year

A season is the main period of the year with a particular type of weather

It is caused by the tilt of the earth’s axis and the earth’s revolution around the sun

In its revolution around the sun, one of these hemispheres is inclined towards the sun at one period of the year. e.g. in December, January and February the southern hemisphere tilts towards the sun. This is summer time the same month in northern hemisphere experiences winter season.

Because the northern hemisphere tilts away from the sun. Springs and autumn are short seasonal transition between summer and winter

Springs is a short season towards summer while autumn is a short season towards winter

Types of season in the year

There are four seasons in the year differentiated by temperature and rainfall characteristics

1. summer
2. Autumn
3. Winter
4. Spring

These four seasons are more pronounced in areas found between latitude 23 and 66 ½ north and south of the equator. Around 0ᵒ to 5ᵒ north and south of the equator never experience season because throughout the year the sun is almost overhead. This experience high temperature and rainfall

The areas between 5ᵒ and 23 ½ᵒ north and south of the equator are characterized by hot- wet and cold dry seasons

The NP and SP are very cold throughout the year and difficult to distinguish the season of the year.

• In the Northern hemisphere,Summer months are June, July and August.Autumn months are September October and NovemberWinter season occur in December, January and FebruarySpring months are March, April and may.
• In southern hemisphere theSummer months are December, January and February,Autumn occur in June, July and august whereSpring months are September, October and November.

Changes of Over Head Sun

The overhead sun appear to move northward and southward between latitude 23 N and 23 s tropic (between tropic of cancer and Capricorn

Example during summer solstice in northern hemisphere, the sun is directly overhead at the tropic of cancer, while during winter solstice, it is directly overhead at the tropic of Capricorn.

The places south of tropic of Capricorn and north of the tropic of cancer never experience overhead sun at any time of the year.

Solstice and Equinox

Solstice: occurs when the earth’s poles are inclined towards or away from the sun, causing the earth’s pole inclined towards the sun to receive maximum sunlight.

This makes the most inclined pole towards the sun to experience the longest days in the year

The southern hemisphere summer solstice occur in December 22nd in the tropic of Capricorn. At the same time it is winter solstice in the tropic of cancer.

The northern hemisphere summer solstice occurs on June 21st at the tropic of cancer. At the same time it is winter solstice at the tropic of Capricorn.

The Equinox

Equinox refers to equal length of day and night.

This occurs when the sun is directly overhead at the equator. This results to equal distribution of sun rays between southern and northern hemisphere.

Equinox occur on March 21st and September 23rd every year. The March equinox is referred to as vernal equinox in northern hemisphere.

September equinox is known as autumnal equinox in the northern hemisphere and vernal equinox in the southern hemisphere.

Varying length of day and night at different times of the year

Places along equator experiences nearly equal day and night throughout the year, but northward or southwards of the poles, the length of the day and night vary with latitude.

Example when the overhead sun is in the northern hemisphere, the days are longer than the night.

At the North Pole (90ᵒs) darkness is experience for six months.

In contrast when the overhead sun is in the southern hemisphere, days are longer than night. Thus the South Pole (90ᵒs) day light is experienced for six months without sunset.

Aphelion and perihelion

Due to the elliptical shape of the earth’s orbit, the sun is closer to the earth at one point of the year than other.

Aphelion is the furthest position of the earth’s orbit from the sun.

The earth is at Aphelion each year on 4th July  when it is in 152 million kilometers from the sun.

Perihelion is the nearest position of the earth from the sun.

The earth is at perihelion each year on 3rd January when it is 147.3 million kilometers from the sun.

REVOLUTION

Eclipse.

Eclipse is the total or partial obstruction of light from the sun by either the earth or the moon

Eclipse involve three heavenly bodies (sun, moon and earth)

It occurs when the earth or the moon intercepts light from the sun.

Types of Eclipse

There are two types of eclipse

1. Lunar eclipse and
2. solar eclipse

a] Lunar eclipse: occurs when the earth passes between the moon and the sun, thus casting its shadow on the moon.

Phases of the moon

Moon develops different shapes or appearances as seen from the earth.

It takes 29days to complete one cycle to revolve around the earth. Phases are the results are the changing position of the moon earth and the sun relative to each other during revolution.

As the moon orbit the earth, different parts of it surface are illuminated by the sun. The portion of the moon facing the sun is lit while the portion facing away is in darkness.

The angle at which we see the illuminated portion of the moon changes depending on earth’s position in its orbit.

As the earth orbit the sun, the sun light falls on different parts of the moon’s surface causing the moon appearances to change over time

The phases observed

New moon, waning crescent, first quarter(waxing half),waxing gibbous, full moon, waning gibbous, last quarter(waning half), waning crescent.

As the moon revolves around the earth its illuminated parts light the earth during the night.

Also the gravitational force of the moon on the earth causes tides in the earth surface water.

B] The solar eclipse is also known as the eclipse of the sun.

This occurs when the moon passes between the earth and the sun, thus casting its shadow over the earth.

Umbra or total eclipse is when the whole body is obscured i.e completely blocked from the sun’s light.

Penumbra or partial eclipse is when only part of the body becomes obscured.

Significances of eclipse

1. Eclipse facilitates scientific exploration
2. It is important in astronomical discoveries: it has facilitated significant discoveries on astronomy
3. It has Cultural and mythical significances
4. Facilitates technological advancement (observation tools and techniques) such as telescopes, cameras have been developed
5. it is significant in Education outreach; They inspire interest in astronomy, space science and natural world
6. It has an impact on the environmental; example sudden decrease in temperature during eclipse can lead to temperature changes.
7. It enhance Global interrelations; eclipse may be witnessed and shared by people all around the world

Parallels And Meridians.

Parallels are more commonly known as Latitudes

Position of place on the earths surface can be found by using parallel and meridians

Latitudes/parallels are imaginaly line paralel to the equator joining places at an equal angular measurement.

The equator divide the Earth into two equal parts called northern and southern hemisphere.

The northern hemisphere has a latitude of 90ᵒN and southern hemisphere has latitude 90ᵒs

Longitudes are also known as meridians

Longitudes: are angular distances measured in degrees east or west of the prime meridian.

They run from north to south.

Greenwich is a longitude 00 . It is also known as prime meridian.

The prime meridian is the line running through the poles (North and South) and is known as greenwich 00

Prime meridian divides the earth into east and west.

Determining latitude

The distance from North Pole to South Pole is about 20000km and there are 180ᵒ.

Example the tropic of cancer is drawn on the surface of the earth with an angular line of 23ᵒN measured ant clockwise from equator.

Latitudes are parallel to each other. They result into uniform width between them.

They have different length decreasing from equator towards the poles

Equator is the longest latitude at the centre of the earth

Thus the distance on the earth surface between one latitude and other must be equal to 111km.

=111

1ᵒ of latitude =111km

Determining longitude

Longitude is an imaginary line measured from east or west of the prime meridian. Its angle is determined by measuring the angle from the centre of the earth along the equatorial plane.

Since the world is about 40000km round the equator and there are 360ᵒ in circle.

The distance between each degree of longitude at the equator must be

=111km

1ᵒof longitude =111km

Since the longitude lines meet at the poles, the distance between degrees of longitudes become progressively less towards the poles.

Great Circle

Great Cycle is a cycle that divides the earth into two equal spheres. The equator and Greenwich meridian are both great cycle.

Similar all other meridians are also great circles. The equator is the only latitude that is a great circle.

Importance’s of great circle

1. They are used in navigation and aviation
2. They are used to plot short routes for ships crossing the ocean to save fuel and time
3. They are the shortest routes between any two places far apart on the earth surface.
4. Longitudes (meridian)  enable us to calculate local and International times of different places on the earth/s surface.

Importance of latitude and longitudes

1. Latitudes determine variation in temperature. Example temperature decrease from equator towards the poles
2. They are used to calculate local time of different places on the earth surface
3. They enable us to precisely to identify any location on the earth
4. They enable us to identify routes for aviation and navigation
5. They help in forming a grid system essential for mapping and communication of geographic data worldwide.
6. They are used to determine days and dates in the world with reference to the international date line
7. They help to determine distances between places on the earth’s surface.

Calculating Local Time Using Longitudes

The earth rotates on its own axis from west to east once after every twenty four hour (1 day).

This means the earth turns through 360ᵒ in 24hrs

It rotates 15ᵒ in 1hr or 1ᵒ in 4minutes

All places along the same longitude experience mid day at the same time

Example: If it 12:00 noon in Addis Ababa (39ᵒE, it will also be noon in dar-es- salaam as it is located at 39ᵒE

places along different longitude experiences different time example when it is 12:00 at places like Accra in Ghana or London in England located along the Greenwich meridian (0ᵒ), it will be 1:00pm at all places along longitude 15ᵒE or 11;00am along longitude 15ᵒW.

Time calculation

• In calculating time we use longitude of a given place
• Calculating two places located on the same side of the prime meridian e.g. east to east or west to west. Find the differences in degree of the places by subtracting the degree of the places
• Places located at different sides e.g. east to west add the degrees of the places. Because the more you move toward the east, the more time increase, while the more you move towards the west, the more time decreases

The time recorded along the same longitude is known as local mean time (LMT).

Example;

The local time of Tunis located at 10ᵒE is 03:00 pm, what is the local time of Mtwara located at 40ᵒE?

Given

Longitude Time

Tunis (10ᵒ) E = 03:00pm

Mtwara( 40ᵒ)E = ?

Find the difference in longitudes

40ᵒ-10ᵒ=30ᵒ

If 15ᵒ=1h

30ᵒ=?

Therefore 30ᵒ×1hr=hrs

Since Mtwara is found in the east of Tunis, its time will be ahead of that of Tunis by 2hrs

03:00pm +2hrs = 05:00pm.

Therefore the time in mtwara will be 05:00pm when the local time at Tunis 10ᵒE is 03:00pm.

Example 2

The local time of Washington DC located at 96ᵒW is 05:00pm, Friday. Find the time and day of

Zanzibar 39ᵒE

Given

Longitude time

Washington DC 96ᵒw     05:00

Zanzibar 39ᵒE

?

The difference in degrees between Washington DC and Zanzibar will be

96ᵒ-39ᵒ=135ᵒ

If 15ᵒ=1hr

135ᵒ=?

=9hrs

Since Zanzibar is to the east of Washington DC, time will be ahead of that of Washington by 9hrs

05:00pm +9hrs =02:00 am

Therefore the time in Zanzibar will be 20:00am Saturday.

Calculating the longitude of places using local time.

Example:

Find the longitudinal position of Mogadishu whose local time is 04:40pm, when the local time at Libreville, Gabon located at 10ᵒ is 02:20pm

• Given

Longitude            time

Libreville 10ᵒE            02:20pm

Mogadishu            04:40pm

• To find the difference in degrees of longitude between Libreville and Mogadishu, convert the time differences into minutes

  2hrs20minutes =140 minutes

  The earth rotates 1ᵒin 4minutes

  How many degrees will it take to rotate 140 minutes?

• Differences in degree

×1ᵒ=35ᵒ

Since the time in Libreville is behind that of Mogadishu, then Mogadishu must be located east of Libreville

10ᵒE+35ᵒ=45ᵒE

Therefore the longitude of Mogadishu will be 45ᵒ

Example 2

What is the longitude of lindi hose local time is 08:24pm when the local time in Montevideo Uruguay located at 56ᵒis 02:00pm

• Longitude        time

Montevideo 56ᵒw    02:00pm

Lindi ?            08:24pm

• The difference in time between lindi and Montevideo

08:4-02:00=06:24hrs

• To find the difference in degrees of longitude between lindi and Montevideo convert time into minutes

6hrs and 24minutes =384minutes

Since the earth rotates 1ᵒ in 4minutes

How many degrees ill it take to rotate 384minutes?

×1ᵒ=96ᵒ

• Since the time of lindi is ahead of that of Montevideo, lindi must be located east of Montevideo

Therefore the longitude of lindi will be

96ᵒ-56ᵒ=40ᵒE

Time Zones

Time one is a stretch of land where the standard time is accepted throughout the longitudinal zones of 15ᵒ in width.

The world is divided into 4 time zones, each approximately 15ᵒlongitide apart. There would be problem in telling time if every place had its own time set according to the local mean time (LMT).

Essence of time and time zones

The essence resulted from difficulties in identifying time for a particular area. If each place across a country followed its on local time, it would create confusion. For example Dodoma is about 35ᵒE and Tanga is 39ᵒE. If each followed its own local time, there would be a difference of 16minutes between two towns.

There would be confusion in railway and airway timetable or radio programs if they had different in time each reflecting to its local area .To avoid this different stretches of land take their time from agreed Meridian. The time adopted is known as standard time. In E.A standard time is taken from Meridian 45degrees E. The Greenwich Meridian is the starting point for dividing the globe into 24 time Zones. The standard time for Greenwich is known as the Greenwich Meridian [GMT]

Variation of standard time in a single country

Country with large stretch of land for example Russia, the united states of America, Canada and China have several standard time Zones for practical purposes.

International date time.

Is an imaginary line where date is changed or calendar day begin. This line is internationally agreed upon and follows the meridian 180ᵒW (or E) longitude except where it crosses land surface.

The IDL is not straight for the purpose of avoiding crossing land Masses which would cause a country to have two different days at the same time