chapter 16 the solar system sections 16.1-16.6. copyright © houghton mifflin company. all rights...

Chapter 16

The Solar System

Sections 16.1-16.6

Copyright © Houghton Mifflin Company. All rights reserved. 16 | 2

Introduction

• Astronomy – the scientific study of the universe beyond Earth’s atmosphere

• Universe – everything, all energy, matter, and space

• Milky Way Galaxy – one of 50 billion galaxies scattered throughout the universe

• Solar System – contains our sun and ~8 planets

• Sun – supplies the energy for nearly all life on the planet earth

Intro


Electromagnetic Spectrum

Astronomers are interested in studying the full range of electromagnetic spectrum coming from space

Intro


Astronomy

• But, much of the incoming solar radiation does not make it to the earth’s surface – due to atmospheric absorption

• Electromagnetic radiation that will pass through the earth’s atmosphere can be studied using ground-based detectors

• Other regions of the electromagnetic spectrum must be detected by space-based instruments– The Hubble Space Telescope is a good example

of an instrument outside Earth’s atmosphere

Intro


VLA (Very Large Array) near Socorro, NM

Copyright © Bobby H. Bammel. All rights reserved.

Intro


Telescopes at the top of Mauna Kea, Hawaii

Photo Source: Bobby H. Bammel

Intro


Astronomy - Relevance

• Ancient Cultures – made numerous solar, lunar, and celestial observations– 365-day year – solar cycle– 29.5-day month – lunar cycle– Calendars – agricultural & religious– One of the Mayan calendars had 18 months of 20

days & 1 month of 5 days (365 days total)

• Modern Cultures – celestial cycles still relevant– celebrate birthdays annually, – academic years, seasons, monthly bills

Intro


The Solar System

• The solar system - complex system of moving masses held together by gravitational forces

• Sun is center

• Sun is the dominant mass

• Revolving around the sun -- 8 planets, over 70 moons, 1000’s of other objects (asteroids, comets, meteoroids, etc.)

Section 16.1


The Solar System

• Geocentric Model – early belief that the earth was motionless and everything revolved around it– Claudius Ptolemy (A.D. 140)

• Heliocentric Model – a sun-centered model– Nicolaus Copernicus (1473-1543) – Polish

Roman Catholic cleric and mathematician, the “founder of modern astronomy”

Section 16.1


Johannes Kepler (1571-1630)

• German mathematician and astronomer

• Kepler’s 1st Law – Law of Elliptical Paths – All planets move in elliptical paths around the sun with the sun as one focus of the ellipse

• An ellipse is a figure that is symmetric about two unequal axes

Section 16.1


Drawing an Ellipse

• An ellipse has two foci, a major axis, and a semimajor axis

• In discussing the Earth’s elliptical orbit, the semimajor axis is the average distance between the earth and the sun Astronomical Unit (AU) = 1.5 x 108 km

Section 16.1


Kepler’s Second Law

• Law of Equal areas – An imaginary line (radial vector) joining a planet to the sun sweeps out equal areas in equal periods of time

Section 16.1


The speed of a revolving planet varies

• Perihelion – the closest point in a planet’s orbit around the sun, speed is the fastest– Perihelion occurs for Earth about January 4

• Aphelion – the farthest point in a planet’s orbit around the sun, speed is the slowest– Aphelion occurs for

Earth about July 5

Section 16.1


Kepler’s Third Law

• Harmonic Law – the square of the sidereal period of a planet is proportional to the cube of its semimajor axis

• T2 = k R3

• T = period (time of one revolution)

• R = length of semimajor axis

• k = constant (same for all planets) = 1y2/AU3

Section 16.1


Calculating the Period of a Planet - Example

• Calculate the period of a planet whose orbit has a semimajor axis of 1.52 AU

• T2 = k R3

• T2 = 3.51y2

• T = 1.87 y

• This is for Mars

Section 16.1

1y2

AU3• T2 = x (1.52 AU)3


Newton’s Correction

• T2 = k R3 (Kepler’s)

• This correction takes into account the mass of the bodies and their gravitational attraction

• Rearranging the above equation will give

Section 16.1

4π2

(m1 + m2)G• T2 = x R3 (Newton’s)

T2

R3

4π2

G• (m1 + m2) =


Our Solar System

• Sun – 99.87% of the mass of solar system

• Of the remaining 0.13%, Jupiter is > 50%

• Planets with orbits smaller than earth are classified as “inferior”

• Planets with orbits larger than earth are classified as “superior”

Section 16.1


Revolution/Rotation• All planets revolve (orbit) counterclockwise (prograde motion)

around the sun as observed from the north pole. Each planet also rotates counterclockwise on its axis except Venus and Uranus (retrograde motion).

Section 16.1


Planet Classification

• Terrestrial planets – Mercury, Venus, Earth, Mars– High percent of more massive (non-

gaseous) elements

• Jovian planets - Jupiter, Saturn, Uranus, Neptune– High percent of less massive gaseous

elements

Section 16.1


The Solar System -- drawn to scale

Section 16.1


The Solar SystemInclination of the planets’ orbit to earth’s

Section 16.1


A Planet’s Period

• Sidereal Period – the time it takes a planet to make one full orbit around the Sun relative to a fixed star

• Synodic Period – the time interval between two successive conjunctions of the planet with the Sun as observed from Earth

conjunction – two objects (a planet and the Sun) are together on the same meridian

Section 16.1


Mercury

• Sidereal = P1 P1 = 88 Earth Days• Synodic = P1 P1 P3= 116 Earth Days

Section 16.1


Planet Earth

• The Earth is the third planet from the sun, and is a solid, spherical, rocky body with oceans and an atmosphere

• Large amounts of surface water in all three phases – solid, liquid, and gas – exist on Earth

• An oxygen-containing atmosphere, temperate climate, and living organisms all make Earth a unique planet

Section 16.2


Composition of the Earth

• Atmosphere – 21% oxygen• Earth’s crust – over 90%, by volume, of

the rocks/minerals are oxygen!• We live in an oxidized environment• Examples of very common minerals at

the earth’s surface include: – Quartz – SiO2, Calcite – CaCO3, Feldspar –

KAlSi3O8

• Note that most common minerals have oxygen (O) in their formula

Section 16.2


Common rocks at surface include granite and marble

copyright © Bobby H. Bammel. All rights reserved.

These rocks contain the minerals SiO2, CaCO3, & KAlSi3O8

Section 16.2


Earth’s Shape

• The planet Earth is not a perfect sphere, but rather an oblate spheriod– Flattened at the poles– Bulging at the equator– Due to rotation about its axis

• Pole Diameter is about 43 km less than the Equatorial Diameter– Since the earth has an average diameter of

12,900 km this difference is only a small fraction

Section 16.2


Albedo

• Albedo – the fraction of the incident sunlight reflected by an object

• Earth’s albedo is 33%• Moon’s albedo is 7% (from Earth the

moon is the 2nd brightest object in the night sky)

• Venus’ albedo is 76% (3rd brightest is sky)

• Since the Moon is so close to Earth it is brighter than Venus

Section 16.2


Earth Motions

• Daily Rotation on its axis (daily cycle)– Rotation – spin on an internal axis

• Annual revolution around the sun (annual cycle)– Revolution – movement of one mass

around another

• The slow change of the earth’s rotational axis (now at 23.5o)

– Precession – Chapter 16

Section 16.2


Earth’s Rotation on its Axis

• Not generally accepted until 19th century

• Very difficult to prove???

• 1851, experiment designed by French engineer, Jean Foucault

• The Foucault Pendulum – very long pendulum with a heavy weight at the end

• Basically, the Foucault pendulum will swing back and forth as the earth moves under it

Section 16.2


Foucault Pendulum

16.2

The pendulum does not rotate with reference to the fixed stars. Experimental proof of the earth’s rotation

Section 16.2


Parallax

• Parallax – the apparent motion, or shift, that occurs between two fixed objects when the observer changes position

• Parallax can be seen with outstretched hand

• The motion of Earth as it revolves around the sun leads to an apparent shift in the positions of the nearby stars with respect to more distant stars

Section 16.2


Stellar Parallax

• The observation of parallax is indisputable proof that the Earth revolves around the Sun.

• In addition, the measurement of the parallax angle is the best method we have of determining the distance to nearby stars

Section 16.2


Aberration of Starlight

A 2nd proof of Earth’s orbital motion• Telescopic observations of a systematic

change in the position of all stars annually– Due to the motion of the earth around the sun

• Angular discrepancy between the apparent position of a star and its true position, arising from the motion of an observer relative to the path of the beam of light observed

Section 16.2


Aberration of Starlight

• This discrepancy is very small and is measured in a -- parsec

• Parsec parallax + second

• Recall that a circle contains 360o. Each degree is divided into 60 minutes, and each minute into 60 seconds

• Therefore 1 second = 1/3600 degree

• Parsec = the distance to a star when the star exhibits a parallax of 1 second.

Section 16.2


Terrestrial Planets

• The terrestrial planets include: Mercury, Venus, Earth, Mars

• Due to physical/chemical characteristics they resemble Earth

• All four terrestrial planets are – Relatively small in size and composed of rocky

material and metals– Relatively close together and close to Sun– Have no rings– Only Earth and Mars have moons– Only Earth has surface water and oxygen

Section 16.3


The Terrestrial Planets, Jovian Planets, and Earth's Moon

Section 16.3


Mercury

• Mercury is the closest planet to the sun• Mercury has the shortest period of revolution

(88 days), and is the fastest moving• Mercury was named by the early Greeks after

the swift messenger of the gods• Temperatures on Mercury range from about

473 oC on the side facing the sun to about -173 oC on the dark side

• Due to its small size and closeness to the sun, Mercury has practically no atmosphere

Section 16.3


Mercury, a Terrestrial Planet

Rotates 3 times while circling the Sun twice

Section 16.3


Venus

• Venus is the closest planet to Earth• Venus is the third brightest object in the sky• Due to its brightness it was named after

Venus the goddess of Beauty• The surface of Venus cannot be seen from

Earth, due to dense, thick clouds that cover the planet

• Magellan radar images indicate that the surface of Venus is composed of black, hot rock– Most surface rocks appear to be volcanic

Section 16.3


The Atmosphere of Venus

• Venus’ atmosphere is composed of 96% CO2

• It is so dense that the surface of Venus has a pressure of 90 atm

• The large percent of CO2 in the atmosphere results in high surface temperatures (477 oC) due the “greenhouse effect”

• Radar images have revealed relatively few impact craters– Most of these craters are fairly large, because the

smaller incoming objects are consumed by Venus’s thick atmosphere

Section 16.3


Venus, a Terrestrial Planet

Atmosphere rotates faster than solid planet.Retrograde rotation possibly caused by impact??

Section 16.3


Mars

• Mars has a red color, as viewed from the Earth, and was named for the Roman god of war

• The surface of Mars has two outstanding features that have intrigued scientists for decades; polar ice caps and extinct volcanoes

• The ice caps are composed of frozen CO2 in the winter and CO2 vapor with frozen water in the summer

Section 16.3


Martian Volcano – Mt. Olympus

• The largest known volcano in the solar system, at 24 km in height, it is about three times that of Mauna Loa

Section 16.3


Mauna Loa & Mauna KeaAbout 9 km above the ocean floor base

Section 16.3


Mars – Valles Marineris

This canyon on Mars is 4000 km in length and 6 km deep

Geologists think that it is a crustal fracture caused by internal forces

Section 16.3


Mars, a Terrestrial Planet

Section 16.3


The Jovian Planets

• Jupiter, Saturn, Uranus, Neptune • Much larger than the terrestrial planets• Composed mainly of hydrogen and helium

– The four Jovian planets have a very low average density (approximately 1.2 g/cm3)

• All four are thought to have a rocky core composed of iron and silicates

• Thick layers of frozen methane, ammonia, and water are found above the core

Section 16.4


Formation of the Terrestrial Planets

• The two least massive elements – H & He – were the most abundant when the planets started to coalesce about 5 billion years ago

• Due to the heat from the sun most of these less massive elements escaped the gravitational pull of the inner planets– Leaving behind more of the massive

elements and resulting in thick rocky cores and higher densities for the inner planets

Section 16.4


Formation of the Jovian Planets

• The four large outer planets were much farther from the sun and therefore much colder

• The Jovian planets retained most of their H and He which now surround their ice layers and innermost rocky cores

• As a consequence the Jovian planets have a much lower average density

Section 16.4


Jupiter

• Largest planet of the solar system, in both volume and total mass

• Named after the supreme Roman god of heaven because of its brightness and giant size

• Diameter is 11 times Earth’s -- 318 times more mass than Earth

• The average density of Jupiter approximately 1.3 g/cm3

• Jupiter is covered with a thin layer of clouds composed of hydrogen, helium, methane, ammonia, and several other substances

Section 16.4


Jupiter

Section 16.4


Jupiter’s Great Red Spot (“eye”)

• The Great Red Spot has erratic movement, shape, color, and size – sometimes even disappearing

• Likely a huge counterclockwise “hurricane-like” storm, lasting hundreds of years

Section 16.4


Saturn

• Distinctive system of three prominent rings– Rings are inclined 27o to orbital plane

• The rings are thought to be composed of ice and ice-coated rocks (micrometers 10 m)

• Most spectacular sight that can be viewed from Earth with a small telescope

• Diameter is 9 times Earth’s -- 95 times more mass than Earth

• Average density of only 0.69 g/cm3

Section 16.4


Saturn

Section 16.4


Roche Limit (Tidal Stability Limit)

• Orbiting moons are held together by their gravity

• As a moon comes closer to a planet the differential gravitational (tidal) force on it increases

• As a moon is brought closer, a point is reached where the tidal force is greater than the internal gravitational forces holding the planet together – and the moon is torn apart

• This critical distance is called the Roche limit

Section 16.4


Formation of Saturn’s Rings

• Saturn’s rings are thought to have originated as small moons that came within their Roche limit and were torn apart

• The Roche limit of Saturn is approximately 2.4 times the planet’s radius

• Saturn’s outer ring is located at a distance of 2.3 times the planet’s radius

Section 16.4


Uranus

• Discovered in 1781 by William Herschel (1738-1822), an English Astronomer

• Named after Uranus, the father of the Titans and the grandfather of Jupiter

• Thin ring system composed of boulder-size particles (>1m), with very little dust-size


Section 16.4


Uranus

Section 16.4


Neptune

• Discovered in 1846 by Johann Galle, a German astronomer

• Englishman John Couch Adams and Frenchman U.J.J. Leverrier were mathematicians using Newton’s law of gravitation

• They noted that Uranus’ motion was disturbed and predicted the location of another planet – this is how Galle eventually discovered Neptune

Section 16.4


Neptune

• Neptune also has a large dark spot similar to Jupiter’s and thought to be the result of large wind systems

• Neptune and Uranus are similar in size and in the composition of their atmospheres

• In many respects these two planets can be considered twins

Section 16.4


Neptune

Section 16.4


Terrestrial versus Jovian

• relatively small in mass and size

• composed of rocky material and metals (having a core mostly of iron and nickel)

• relatively dense (~5 g/cm3)

• solid surfaces • weak magnetic fields• no ring systems

• relatively large in mass and size

• composed mainly of hydrogen and helium (rocky core with layers of ice above it)

• low density • (~1.2 g/cm3) • no real surfaces;• strong magnetic fields• many moons and ring

systems


Pluto

• Names for the god of outer darkness


• Discovered in 1930, by C.W. Tombaugh– Investigating discrepancies in the orbital

path of Neptune and Uranus

• Does not resemble either the terrestrial or Jovian Planets

• Pluto is the only planet that has not been visited by a space probe

Section 16.4


Pluto

• Now classified as a “dwarf planet”• There are similarities between Pluto and

Triton, of Neptune’s moons• Some scientists think that both are large

asteroids captured from interplanetary space

• If this is the case, Pluto has maintained its own orbital path, and Triton was captured by Neptune

• Three satellites: Charon, Hydra, & NixSection 16.4


Pluto and one of its satellites Charon

Section 16.4


Sedna

• Discovered in 2003• ¾ the size of Pluto• Located in the Kuiper Belt• Not thought to be a KBO• Elongated 10,500-year period

Kuiper Belt – a part of the solar system located outside of Neptune’s orbit where many short-period comets orginate.


Eris

• Formerly known as 2003UB313

• Largest of the known Dwarf Planets in our solar system

• 1 moon – Dysnomia

• Are located farther away from the Sun than any other known object in our solar system with the exception of comets


Origin of the Solar System

• Any theory that purports to explain the origin and development of the solar system must account for its present form

• According to our best measurements, our solar system has been in its present state for about 4.5 billion years

• A valid theory for solar system formation – must be able to explain a number of major properties of our solar system

Section 16.5


Major Questions Concerning Solar System

• Origin of material?• Forces that formed the solar system?• Isolated planets, circular orbits, in same

plane?• Revolution (orbit) in the same direction?• Most Rotate in same direction (except two)?• Terrestrial versus Jovian planets?• Origin of the asteroids?• Origin of comets and meteoroids?

Section 16.5


Formation of the Solar System

• Began with a large, swirling volume of cold gases and dust – a rotating primordial nebula (or solar nebula)

• Contracted under the influence of its own gravity – into a flattened, rotating disk

• Further contraction produced the protosun and eventually accreted the planets

• As particles moved inward, the rotation of the mass had to increase to conserve angular momentum (like an ice skater bringing in her arms)

Section 16.5


The Formation of the Solar SystemCondensation Theory

Section 16.5


Other Planetary Systems

• Are there other planetary systems in the universe?

• If so, we would expect to find some of these systems in different stages of formation– In other words, we should be able to find clouds of

gas and dust, primordial nebula, and protosuns, etc.

• We should also be able to use gravitational effects to detect small wobbles in rotational objects in space

Section 16.6


Gravitational Effects

• A star with a large planet orbiting about it will have a small wobble superimposed on its motion as a result of gravitational effects

• This change in motion (the wobble) is likely to be very slight, but in some cases may be detected as a Doppler shift of the star’s spectrum– As the star approaches the observer, the

wavelengths are compressed (‘blue shift’)– As the star move away from the observer, the

wavelengths are lengthened (‘redshift’)

Section 16.6


Gravitational Effects

• The amount of wobble can be used to determine the planet’s mass (related to gravitational pull)

• The wobble’s cycle time can be used to determine the orbital period

• Once the orbital period is known, Kepler’s third law (T2= kR3)can be used to determine the planet’s average distance from the star

Section 16.6


System First Planets Discovered Beyond our Solar System

• In 1992, using the Arecibo Observatory in Puerto Rico, astronomers reported the discovery of two objects revolving about a pulsar– Pulsars are very dense, rapidly rotating stars– Pulsars have a very precise rotation period– If the rotation period is disrupted, this would

indicate the presence of an object rotating about the pulsar

• These two objects are the first planets detected beyond our solar system

Section 16.6


Planets Beyond our Solar System

• As of 2007, there have now been 241 planets detected around other stars1

• These findings strongly indicate the existence of many other planetary systems in the universe

1http://vo.obspm.fr/exoplanetes/encyclo/catalog.php (The Extrasolar Planets Encyclopaedia)

Section 16.6


SETI

• Scientists are also searching for signals from extraterrestrial intelligence (SETI)

• Equipment today is being used to scan wide frequency ranges over vast areas of the sky

chapter 16 the solar system sections 16.1-16.6. copyright © houghton mifflin company. all rights...

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