chapter three the earth as a planet section one – the planet earth section two– earth motions...

Chapter ThreeChapter ThreeThe Earth as a PlanetThe Earth as a Planet

Section One Section One – The Planet Earth– The Planet EarthSection TwoSection Two – Earth Motions– Earth MotionsSection Three Section Three -- Tools of Astronomy-- Tools of Astronomy

The Earth’s CompositionThe Earth’s CompositionThe Earth is a The Earth is a terrestrial planetterrestrial planet..

Definition: a planet that is composed mostly of rockDefinition: a planet that is composed mostly of rock– A planet is a large body that travels around a star.A planet is a large body that travels around a star.– The term terrestrial means that it is made mostly of rock The term terrestrial means that it is made mostly of rock

and metal.and metal.

The land portion of our planet is known as the lithosphere and The land portion of our planet is known as the lithosphere and

is divided into 4 parts is divided into 4 parts (starting with the innermost)(starting with the innermost)::– INNER CORE/OUTER CORE: INNER CORE/OUTER CORE: a dense combination of a dense combination of

molten iron and nickelmolten iron and nickel

– MANTLE: MANTLE: plastic-like, less dense rockplastic-like, less dense rock

– CRUST: CRUST: the outer portion of the Earth, made up of two basic the outer portion of the Earth, made up of two basic types of solid rock (granites and basalts)types of solid rock (granites and basalts)

Granite rocks make up most of the Earth’s continents; Granite rocks make up most of the Earth’s continents; basalts compose most of the ocean floor.basalts compose most of the ocean floor.

Along with the lithosphere, here are two other parts Along with the lithosphere, here are two other parts that make up our Earth – that make up our Earth – the atmosphere and the the atmosphere and the hydrosphere.hydrosphere.

The Earth’s ShapeThe Earth’s ShapeThe shape of the Earth is The shape of the Earth is nearly sphericalnearly spherical, which , which means it resembles a round ball.means it resembles a round ball.– Before there was hard evidence to support the shape of our Before there was hard evidence to support the shape of our

planet, humans theorized about its shape. Some hints that planet, humans theorized about its shape. Some hints that they had are stated below:they had are stated below:

1.1. The disappearance of ships as they moved over the The disappearance of ships as they moved over the horizon.horizon.

2.2. Ancient astronomers observed a curved shadow Ancient astronomers observed a curved shadow move across the moon during a lunar eclipse.move across the moon during a lunar eclipse.

3.3. The altitude of the North Star changed as they The altitude of the North Star changed as they moved farther south or north.moved farther south or north.

Currently, scientists have developed the technology Currently, scientists have developed the technology needed to prove the round shape of the Earth.needed to prove the round shape of the Earth.– However, it is not perfectly round – it is referred to as However, it is not perfectly round – it is referred to as

an an oblate spheroidoblate spheroid..

The term oblate means that it is slightly flattened.The term oblate means that it is slightly flattened.

The slight flattening of the Earth near the equator is The slight flattening of the Earth near the equator is caused by it’s rapid rotation – caused by it’s rapid rotation – that means that the that means that the diameter is slightly larger around the equator than around diameter is slightly larger around the equator than around the polesthe poles..

The The equatorial diameter equatorial diameter of the Earth is of the Earth is approximately approximately 7,928 mi7,928 mi, whereas the , whereas the diameter diameter between the North and South Polesbetween the North and South Poles is is 7,900 mi7,900 mi..

The Size of the EarthThe Size of the EarthThe total surface area of the Earth is approximately The total surface area of the Earth is approximately 197 million square miles.197 million square miles.– More than 70% is covered by ocean.More than 70% is covered by ocean.

The Earth’s RotationThe Earth’s RotationThe Earth rotates on it’s The Earth rotates on it’s axisaxis, connecting the North and , connecting the North and South Poles.South Poles.

DefinitionDefinition: a straight line around which an object rotates: a straight line around which an object rotates– Early astronomers questioned whether the heavens Early astronomers questioned whether the heavens

were spinning around the Earth, or the Earth was were spinning around the Earth, or the Earth was spinning on an axis.spinning on an axis.

The speed at which the Earth is rotating depends on The speed at which the Earth is rotating depends on how far north or south of the equator you are.how far north or south of the equator you are.– If you are standing near the equator, the rotational If you are standing near the equator, the rotational

speed is approx. 1,037 mph.speed is approx. 1,037 mph.

At this speed, the Earth makes one full At this speed, the Earth makes one full rotationrotation..DefinitionDefinition: the circular movement of a body around a : the circular movement of a body around a central point called an axiscentral point called an axis

– A full rotation takes A full rotation takes 23 hours23 hours, , 56 minutes56 minutes, and , and 4.1 seconds4.1 seconds – – but we round it up to 24 hours, or 1 day.but we round it up to 24 hours, or 1 day.

The rotation of the Earth causes half the world to be The rotation of the Earth causes half the world to be exposed to sunlight while the other half is bathed in exposed to sunlight while the other half is bathed in darkness.darkness.– This is why we experience day and night This is why we experience day and night – – and helps define and helps define

the Earth’s weather and climate regionsthe Earth’s weather and climate regions..

The Earth’s Tilted AxisThe Earth’s Tilted AxisThe axis of the Earth is tilted approximately 23.5 The axis of the Earth is tilted approximately 23.5 degrees.degrees.– The tilt of the Earth’s axis causes parts of the Earth to The tilt of the Earth’s axis causes parts of the Earth to

receive more sunlight than other parts receive more sunlight than other parts – – causing the four causing the four seasonseason. .

The first day of summer in the The first day of summer in the Northern HemisphereNorthern Hemisphere is called the is called the summer solstice summer solstice and the first day of and the first day of winter is called the winter is called the winter solsticewinter solstice..– The summer solstice usually falls around June 21The summer solstice usually falls around June 21stst and is and is

that day that has the longest period of daylight.that day that has the longest period of daylight.– The winter solstice usually falls around December 21The winter solstice usually falls around December 21stst and is and is

the day that has the shortest period of daylight.the day that has the shortest period of daylight.

Days in which periods of daylight and night are Days in which periods of daylight and night are equal equal lengthlength are referred to as equinoxes are referred to as equinoxes (the sun is directly (the sun is directly

overhead at the equator)overhead at the equator)..– Every year, two equinoxes occur Every year, two equinoxes occur – the – the vernal equinoxvernal equinox and and

the the autumnal equinoxautumnal equinox..– The The vernal (spring) equinox vernal (spring) equinox usually falls around March usually falls around March

2121stst, and the day and night are each 12 hours in length., and the day and night are each 12 hours in length.– The The autumnal (fall) equinox autumnal (fall) equinox usually falls around September usually falls around September

2323rdrd, and the day and night are each 12 hours in length., and the day and night are each 12 hours in length.

The Earth’s Coordinate System:The Earth’s Coordinate System:Latitude and LongitudeLatitude and Longitude

A coordinate system is a method of locating an exact A coordinate system is a method of locating an exact location on a two-dimensional surface.location on a two-dimensional surface.– The The equatorequator divides the planet into two hemispheres. divides the planet into two hemispheres.

DefinitionDefinition: the imaginary line, also known as zero degrees : the imaginary line, also known as zero degrees latitude, that divides the Earth in half into the Northern and latitude, that divides the Earth in half into the Northern and Southern HemisphereSouthern Hemisphere

– Each hemisphere is further divided by horizontal lines Each hemisphere is further divided by horizontal lines that mark the locations north and south of the equator that mark the locations north and south of the equator called lines of called lines of latitudelatitude..

DefinitionDefinition: parallel lines the run east and west across Earth’s : parallel lines the run east and west across Earth’s surface, measuring locations north and south of the equatorsurface, measuring locations north and south of the equator

– These lines are marked in degrees – These lines are marked in degrees – the equator being the equator being represented by 0represented by 0oo, and increasing in both directions as , and increasing in both directions as you move away from the equator lineyou move away from the equator line..

Lines of latitude are useful only for determining an Lines of latitude are useful only for determining an exact location either north or south of the equator – exact location either north or south of the equator – they become more helpful if used in combination with they become more helpful if used in combination with the lines of the lines of longitudelongitude..

DefinitionDefinition: coordinate lines used on the earth’s surface : coordinate lines used on the earth’s surface that run north and south from pole to pole and measure that run north and south from pole to pole and measure a location east and west of the prime meridiana location east and west of the prime meridian

– Degrees of longitude are also marked by degrees, only Degrees of longitude are also marked by degrees, only there is no natural halfway point that divided the Earth there is no natural halfway point that divided the Earth vertically vertically – – so astronomers have designated a place on so astronomers have designated a place on our planet our planet (called the prime meridian) (called the prime meridian) to represent 0to represent 0oo degrees.degrees.

Topographical MapsTopographical MapsMaps the we use to represent a three-dimensional Maps the we use to represent a three-dimensional surface of the Earth are called topographical maps.surface of the Earth are called topographical maps.

They represent changes in elevation on the Earth’s They represent changes in elevation on the Earth’s surface by using surface by using contour lines contour lines they are drawn on a they are drawn on a map to represent a specific elevation of the land surface map to represent a specific elevation of the land surface above sea level.above sea level.

DefinitionDefinition: isolines that mark areas of equal elevation on a : isolines that mark areas of equal elevation on a topographical map topographical map

– By adding contour lines to a map, it is possible to see By adding contour lines to a map, it is possible to see the true shape of the land.the true shape of the land.

Also found on a topographical map, along with contour Also found on a topographical map, along with contour lines, are lines, are contour intervalscontour intervals..

DefinitionDefinition: the specific change in elevation associated : the specific change in elevation associated with each contour line on a topographical mapwith each contour line on a topographical map

– Each contour interval is represented as the blank space Each contour interval is represented as the blank space between two lines – between two lines – on a map of this type, each contour on a map of this type, each contour line represents a predetermined increase in height and the line represents a predetermined increase in height and the space between represents the steepness of the land.space between represents the steepness of the land.

Apparent Motion of Celestial ObjectsApparent Motion of Celestial ObjectsBecause our Earth is spinning, objects in the Because our Earth is spinning, objects in the nighttime sky appear to move in regular motions.nighttime sky appear to move in regular motions.– These objects are called celestial objects, which These objects are called celestial objects, which

include planets, moons, stars, comets, asteroids, and include planets, moons, stars, comets, asteroids, and any other object located outside of the Earth’s any other object located outside of the Earth’s atmosphere.atmosphere.

The movement of celestial objects is called apparent The movement of celestial objects is called apparent motion – motion – this apparent motion travels from east to west this apparent motion travels from east to west

across the skyacross the sky..– The speed at which apparent motion travels is measured in The speed at which apparent motion travels is measured in

degrees, with the sky representing 180 degrees from degrees, with the sky representing 180 degrees from horizon to horizon horizon to horizon – – this is broken down so that the speed this is broken down so that the speed of the celestial objects travel is approximately 15 degrees of of the celestial objects travel is approximately 15 degrees of sky per hoursky per hour..

Early Models of the UniverseEarly Models of the UniverseAs a result of the apparent motion of celestial objects, As a result of the apparent motion of celestial objects, for thousands of years humans believed that the for thousands of years humans believed that the planets and stars revolved around the Earth.planets and stars revolved around the Earth.– Claudius Ptolemy, the great Romanian mathematician,

geographer, and astronomer, who lived almost 2,000 years ago, was the first scientist to formulate this idea.

In the Ptolemaic system, or geocentric view of the universe, Ptolemy described the planets and stars are revolving around the Earth in perfect circular orbits.

Definition: an early model of the universe which puts the Earth at the center of the solar system and universe

The Geocentric model was accepted for over one thousand years until Copernicus changed the way that humans looked at the heavens.

Nicolaus Copernicus observed the motions of stars and planets for decades and eventually published his theory called the Copernicus heliocentric system.

Definition: a model of the solar system that puts the Sun at its center with the Earth and other planets revolving around it

– Copernicus’ theory created much controversy, and lacked sufficient proof to verify it.

– Galileo Galilei took up Copernicus’ idea when he used improved telescopes of his own design to help support the heliocentric model.

Galileo first observed the Earth’s moon with his new telescopes revealing that its surface was much like the Earth, consisting of mountains, valleys, and craters.– He then started to observe the moons of other planets and

he noticed that each of those moons were revolving around their planets.

Galileo also observed the surface of the sun with his telescopes.– Although it made him nearly blind, his observations

discovered its unique sunspots.– After carefully plotting the location of these dark patches on

the Sun, he discovered that it was also most likely rotating on its axis, like the Earth.

While Galileo was trying to prove his theories, the work of German astronomer, Johannes Kepler, caused another breakthrough for modern astronomy.– Kepler used the work of another astronomer to reveal the

true nature of the orbits of the planets– It was previously thought that the orbits were circular, but he

recognized that the only way to accurately explain the positions of the planets was to describe their orbits as being elliptical.

His research is now known as Kepler’s laws of planetary motion:– The first law states that the planets all revolve around the Sun

in elliptical orbits.

– The second law explains that as the planets revolve around the Sun, their velocity changes in relationship to their distance to the Sun.

– The third law explains that the period of time it takes for a planet to orbit the Sun is related to the size of its elliptical path.

Finally in 1687, the English astronomer and mathematician Isaac Newton published his three laws of gravitation- these helped to explain how Kepler’s laws worked.

Getting to this point shows how the advancement of human knowledge progresses through time as scientists build upon the theories of others.

Orbital MotionOrbital MotionThe motions of all celestial objects are based on the concept of an ellipse.

Definition: the oval-like path of the orbit of a celestial object around two points known as foci, one of which is the Sun

– The ellipse can be generally described as the oval-like path of a celestial object.

The path of the ellipse, known as the orbit, is defined by two points, individually known as a focus, and together called foci.

The oval nature of elliptical paths can be mathematically described as their eccentricity.

Definition: the mathematical expression of how far as ellipse is from a perfect circle, which can be determined by dividing the distance between the foci by the length of the major axis

An ellipse with an eccentricity of 0 represents a perfect circle and an ellipse with an eccentricity of 1 is regarded as a flat line.– The closer the eccentricity is to 1, the more eccentric or oval

shaped the orbital path is.

– Pluto’s orbit is the most eccentric, or furthest from being a perfect circle.

– Venus has the least eccentric orbit, which is closest to being a perfect circle.

The time it takes for a planet to make one complete orbit around the Sun is called one revolution.

Definition: the movement of an object in an orbit around another object

For the Earth, the perihelion occurs around the first of January, when the Earth is approx. 91,349,000 mi from the Sun.

Definition: the point in a planet’s orbit around the Sun when it is closest to the Sun

For the Earth, the aphelion happens during the first week in July, when the Earth is approximately 94,454,000 miles from the Sun.

Definition: the point in the orbit of a planet when it is farthest from the Sun

– Although the distance from the Earth to the Sun changes as a result of its elliptical orbit, this does not affect the Earth’s climate- the Earth’s tilted axis has a much greater effect on seasonal change and temperature than the aphelion or perihelion.

Kepler’s second law describes how the velocity (speed)

of a planet changes in its orbital path relative to its distance from the Sun.– When the Earth is at its closest position to the Sun, the

increased gravitational attraction causes an increase in the velocity.

– When the Earth is at its farthest position to the Sun, the decreased gravitational attraction causes a decrease in the velocity.

Knowledge of the elliptical orbits of planets and how they are governed by gravity has become a useful tool for exploring outer space.– Astronomers have put this knowledge to practical use with

what is called gravity assist.

Definition: a technique also known as the “slingshot” effect which is used to control the direction and velocity of many interplanetary spacecraft by applying an understanding of elliptical orbits and gravitational acceleration

Locating Celestial ObjectsLocating Celestial ObjectsAstronomers have used various coordinating systems, known as celestial coordinates, to help them map the locations of celestial objects, and also track their movements.– One of these systems is called the horizontal coordinate

system – this uses coordinates called azimuth and

altitude to mark precise locations in the sky.

AZIMUTH: the location of an object around the horizon, which is divided into the 360 degrees of a circle.

ALTITUDE: the angle of a celestial object above the horizon, which represents an angle between 0 and 90 degrees.

– The horizon represents 0 degrees of altitude with the zenith representing 90 degrees above the horizon.

Definition: the point in the sky that is directly above the observer, or 90 degrees above the horizon

Another system more widely used by astronomers is Another system more widely used by astronomers is called the called the equatorial coordinate systemequatorial coordinate system..– This system is based on Earth’s latitude/longitude This system is based on Earth’s latitude/longitude

coordinate system, which is extended out into what is called coordinate system, which is extended out into what is called the celestial sphere.the celestial sphere.

TelescopesTelescopesProbably the most widely used tool of astronomers is Probably the most widely used tool of astronomers is the telescope.the telescope.

Definition: a scientific instrument used to observe objects that are far away

– Galileo was the first person we know of to use this Galileo was the first person we know of to use this device to observe celestial objects.device to observe celestial objects.

There are There are threethree basic types of basic types of optical telescopesoptical telescopes..Definition: a telescope that uses glass lenses and mirrors to magnify the light given off by an object

BASIC TYPES:BASIC TYPES:– REFRACTING TELESCOPES REFRACTING TELESCOPES uses a combination of uses a combination of

concave and convex lenses to magnify an image; they concave and convex lenses to magnify an image; they provide clear, high-resolution images of very small sections provide clear, high-resolution images of very small sections of the sky.of the sky.

– REFLECTING TELESCOPES REFLECTING TELESCOPES uses a large concave uses a large concave mirror to focus light to magnify an image; they can have very mirror to focus light to magnify an image; they can have very large apertures providing a wide view of the sky with large apertures providing a wide view of the sky with excellent clarity and brightness.excellent clarity and brightness.

– COMPOUND TELESCOPES COMPOUND TELESCOPES uses a combination of both uses a combination of both lenses and mirrors to provide an excellent high-resolution lenses and mirrors to provide an excellent high-resolution magnification of the sky.magnification of the sky.

One of the limits of ground based optical telescopes is One of the limits of ground based optical telescopes is the distortion and interference caused by the Earth’s the distortion and interference caused by the Earth’s atmosphere.atmosphere.– To alleviate this problem, NASA has designed and launched To alleviate this problem, NASA has designed and launched

space based telescopes like the space based telescopes like the Hubble Space TelescopeHubble Space Telescope..

– This large reflecting telescope orbits the Earth at about 375 This large reflecting telescope orbits the Earth at about 375 miles above the surface of the planet – it provides some of miles above the surface of the planet – it provides some of the highest resolution images of space ever seen by the highest resolution images of space ever seen by astronomers.astronomers.

PhotographyPhotography and and computer technology computer technology also have also have added to the capabilities of optical telescopes.added to the capabilities of optical telescopes.– Many optical telescopes are fitted with Many optical telescopes are fitted with spectroscopesspectroscopes..

Definition: a scientific instrument used to analyze the visible light portion of the electromagnetic spectrum

– These spectroscopes work like a These spectroscopes work like a prismprism, which separates , which separates light into individual colors – light into individual colors – this allows astronomers to this allows astronomers to view the unique spectrum of celestial objectsview the unique spectrum of celestial objects..

A A continuous spectrum continuous spectrum shows all of the colors of shows all of the colors of visible light, however the interaction of visible light visible light, however the interaction of visible light with matter causes specific wavelengths of light to be with matter causes specific wavelengths of light to be absorbed.absorbed.

The wavelengths of light that are absorbed leave gaps in The wavelengths of light that are absorbed leave gaps in the spectrum known as absorption, or the spectrum known as absorption, or dark line spectrumdark line spectrum – – every element and compound has its own unique dark line every element and compound has its own unique dark line signature, which can be used like a fingerprint to identify signature, which can be used like a fingerprint to identify specific substances.specific substances.

DefinitionDefinition: a spectrum of light where specific wavelengths are : a spectrum of light where specific wavelengths are absorbed, leaving gaps in the form of dark lines within the absorbed, leaving gaps in the form of dark lines within the spectrum, also known as the absorption spectrumspectrum, also known as the absorption spectrum

A similar process also occursA similar process also occurs

when objects give off radiation – when objects give off radiation –

this is called an emission, orthis is called an emission, or

bright light spectrumbright light spectrum..DefinitionDefinition: a type of spectrum: a type of spectrum

where bright lines of specificwhere bright lines of specific

wavelengths of visible lightwavelengths of visible light

appear within a spectrum that represent wavelengths of light appear within a spectrum that represent wavelengths of light emitted from a substanceemitted from a substance

Radio telescopes are another type of telescope used by astronomers.

Definition: a type of telescope that senses longer wave electromagnetic radiation in the form of microwaves and radio waves

– The main component is the antennae, which is usually

disk-shaped – they sense radiation from far out into the universe and sends it to computers to be analyzed.

– The radio telescope has made many significant contributions to astronomy, including the detection of the first planets discovered outside of the solar system.

Often a network of radio telescopes is used to create interferometry.

Definition: the combination of radio signals received by a network of radio telescopes used to create one large telescope

Space ExplorationSpace ExplorationSpace exploration is the physical investigation of celestial objects outside of the Earth’s atmosphere – it is undertaken in two fundamental ways.– The first employs the use of robotic spacecraft or

satellites to visit objects in the solar system.– The second is human space-flight, which utilizes

spacecraft to transport humans into space for the purpose of exploration.

One of the most difficult aspects of both methods of space exploration is the problem of getting off the Earth itself.– So far the best way to do this is to use rocketry – rockets

use solid and liquid fuels, which are burned rapidly to create great amounts of thrust that rapidly accelerates the vehicle.

The development of new technologies to propel spacecraft are currently under way, and will certainly play an important role in the future of space exploration.– Cordless power tools, smoke detectors, light emitting

diodes (LEDs), protective helmets, robotics, global positioning systems (GPSs), wireless communication, night vision cameras, heart monitors, and scratch-resistant lenses are just a few of the technologies that are a result of space exploration – this is known as technology transfer.

Definition: the transfer and application of technology to improve quality of life that was developed as a result of scientific investigation

chapter three the earth as a planet section one – the planet earth section two– earth motions...

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