The planet earth
Theories and hypothesis for origin of the earth
The critiques of the theory were put
forward by Pierre Laplace who challenged Immanuel Kant through the following;
a) Larger
amount of heat cannot be generated due
to the collision of cold particles of primordial matter as claimed by Kant.
b) Also
mutual collision of particles cannot generate motion in the primordial matter.
c) More
over the random motion of the particles cannot generate circular motion in the
primordial matter.
d) Also
angular velocity of rotary speed of the nebular cannot increase due to the
increase in size of the nebular as assumed by Kant.
Critiques
of the theory
The
critiques of the theory are that, it appears all galaxies emerged at the same
time; therefore, they could potentially have at least the same age. However,
but this has not been the case, in fact current astronomical researchers have
found that while other galaxies are very old, there are many young galaxies
around and far from the earth.
Inter-
stellar dust hypothesis
In 1943, a Russian scientist Otto Schmidt
proposed a theory known as inter-stellar dust hypothesis. It explains the
complex problems of the origin and characteristics of the solar system and the
earth. According to the inter- stellar dust hypothesis, the sun during its
galactic revolution, captured the dark matter of the universe. The dark matter
[inter stellar dusts] of gaseous cloud and dust particles had their own angular
momentum. The dark matter after being attractive by the sun during its galactic
revolution ‘’started revolving around the primitive rotating sun.
The intense heat from the sun dispersed
the gaseous particles towards the margins of the disk.
Collision among the dust particles started
the process of aggregation and accretion around the bigger particles which
become the essentials of the future planets. With the passage of time, these
embryos captured more and more matter and grew in size to become asteroids.
Furthermore these asteroids grew in size due to continuous acceleration of
nearby matter around them these become planets.
Critique
a)
The hypothesis has been
criticized that gravitational force of the primitive sun was incapable of
capturing dark matter scattered in the universe.
b)
Another critique is that
some astrophysicists’ believe that meteorites and asteroids were formed from
disintegration of planet .They reject the idea that the planets were formed out
of meteorites and asteroids.
Position
of the earth in the solar system
Earth is the third planet in the position
from the sun. It is located about 150 millions km from the sun. And it is the
only planet that supports life due to the presence of water.
It has an atmosphere which contains
different gases essential for living things. Also the position of the earth in
the solar system makes its temperature suitable for plants and animals.
The position of earth in
the solar system
Challenges
facing the planet earth
(a)Climate
change (b) pollution (c) deforestation (e) loss of diversity and (f)
overconsumption of natural resources
Shape
and size of the earth.
The earth is the fifth largest planet in
the solar system in terms of size and mass. Its shape is like flattened sphere
known as an oblate spheroid (geoid).
The distance through the centre from the
North Pole to the South Pole is approximately 12713kms where as the distance
through the centre of the earth at equator is approximately 12757kms.
The
circumference of the earth at the equator is about 40085kms while the polar
circumference is 39955kms.
Evidence to show that
the earth has an oblate spheroid shape(spherical shape of the earth)
There are some several evidences
which are used to prove that the earth is sphere like structure, some of them
are shown as follows
a)
sunrise and sunset
b)
circumnavigation of the earth
c)
aerial photographs
d)
ship’s visibility
e) lunar eclipse
a]Sunrise and sunset
The sunrise and sunset at different places of the earth.
People in the east see the sun earlier than the people in the west due to
earth’s rotation from west to east. If the earth was flat the whole world would
have sunrise and sunset at the same time.
b]Circumnavigation of
the earth
If
traveling from a certain point of the earth and you go straight around the
earth you will come to the point of origin. The first traveler around the world
named Magellan in 1519-1522 proved this.
c]Aerial photographs
Photographs taken by satellites or aeroplane from the air
show that the earth has a curved or round shape.
d]Ship’s visibility
If you are in the coast viewing a ship which is very far
you will see the soot, then the pipe and eventually the whole ship gradually
appears. If the earth were flat the ship would have been seen all at once
spherical earth
flat earth
e]Lunar eclipse
The shadow of the earth thrown to the moon during lunar
eclipse is always round. Only a spherical object can give a circular shadow.
Movement of the earth in the solar system
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 2312
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;
a)
Day and night
b)
sun rise and sun set
c)
Shape of the earth
d)
Star trails
e)
Time zones
f)
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.
a)
Day and night
b) Differences in time
c) Gain or loss of a day
d) Tides:
e) 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
a) Season
of the year
b) Varying length of day and night at different times of the year
c) Changes
of Over Head Sun
d) Aphelion
and perihelion
e) 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
a) summer
b) Autumn
c) Winter
d) Spring
These four seasons
are more pronounced in areas found between latitude 2312
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,
ü Summer
months are June, July and August.
ü Autumn
months are September October and November
ü Winter
season occur in December, January and February
ü Spring
months are March, April and may.
§ In
southern hemisphere the
ü Summer
months are December, January and February,
ü Autumn
occur in June, July and august where
ü Spring
months are September, October and November.
Changes of Over Head Sun
The overhead sun
appear to move northward and southward between latitude 2312ᵒ
N and 2312ᵒ
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.
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
a)
Lunar eclipse and
b) 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 2912
days 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
a.
Eclipse
facilitates scientific exploration
b.
It is
important in astronomical discoveries: it has facilitated significant
discoveries on astronomy
c.
It has
Cultural and mythical significances
d.
Facilitates
technological advancement (observation tools and techniques) such as
telescopes, cameras have been developed
e.
it is
significant in Education outreach; They inspire interest in astronomy, space
science and natural world
f.
It has an
impact on the environmental; example sudden decrease in temperature during
eclipse can lead to temperature changes.
g.
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 2312
ᵒN
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.
20000180ᵒ
=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
40000360
=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
a.
They are used
in navigation and aviation
b.
They are used
to plot short routes for ships crossing the ocean to save fuel and time
c.
They are the
shortest routes between any two places far apart on the earth surface.
d.
Longitudes (meridian) enable us to calculate local and International
times of different places on the earth/s surface.
Importance of latitude and longitudes
a.
Latitudes
determine variation in temperature. Example temperature decrease from equator
towards the poles
b.
They are used
to calculate local time of different places on the earth surface
c.
They enable
us to precisely to identify any location on the earth
d.
They enable
us to identify routes for aviation and navigation
e.
They help in
forming a grid system essential for mapping and communication of geographic
data worldwide.
f.
They are used
to determine days and dates in the world with reference to the international
date line
g.
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×1hr30ᵒ×1hr15ᵒ
=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=?
135ᵒ×1hr15ᵒ
=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
140m 4minutes
×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?
384minutes4minutes
×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.
