Chapter 16 The Solar System
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Chapter 16
The Solar System
Finding the Standard Time and Date at Another Location –Example
• When it is 12 noon in London, what is the standard time in Denver, Colorado (40°N, 105°W)?
Section 15.3
Finding the Standard Time and Date at Another Location – An Example
Section 15.3
12
Noon
5 AM
When it is
12 noon in
London,
what is the
standard
time in
Denver,
Colorado
(40°N,
105°W)?
Finding the Standard Time and Date at Another Location – An Example
Section 15.3
When it is 10 a. m. standard time on February 22 in
Los Angeles (34°N, 118°W), what are the
standard time and date in Tokyo (36°N, 140°E), ?
Finding the Standard Time and Date at Another Location – An Example
Section 15.3
Los Angeles
10 AM 118 W
3:20 AM 140°E
February 23
When it is 10
a. m. standard
time on
February 22 in
Los Angeles
(34°N,
118°W), what
are the
standard time
and date in
Tokyo
(36°N,
140°E), ?
10 AM
3:00 AM
Introduction
• Astronomy – the scientific study of the universe beyond Earth’s atmosphere
• Universe – everything, all energy, matter, and space
• The Milky Way– one of 50 billion galaxies scattered throughout the universe
• Solar System – contains our Sun and 9 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
• 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
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 major planets with over 160 moons, 3 dwarf planets, and 1000’s of other objects (asteroids, comets, meteoroids, etc.)
• Planets.- Greek word “ wanderer”
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)
Section 16.1
Johannes Kepler (1571-1630)
• German mathematician and astronomer
• Interested in the irregular motion of the planet Mars.
• Kepler’s 1st Law – Law of Elliptical Orbits – All planets move in elliptical orbits 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
Example 1
• Calculate the period T of a planet whose orbit has a semimajor axis of 5.2 AU.
K constant of proportionality = 1y2/AU3
Section 16.1
Planet Classification
• Terrestrial planets – Mercury, Venus, Earth, Mars • High percent of more massive (non-gaseous)
elements
• Jovian planets - Jupiter, Saturn, Uranus, and Neptune • High percent of less massive gaseous elements
Section 16.2
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 16.2
The Solar System -- drawn to scale with the eight major planets
Section 16.2
A Planet’s Period
• Sidereal Period – the time interval between two successive conjunctions as observed from the sun
• Mercury’s sidereal period is 88 Earth days
• Synodic Period – the time interval between two successive conjunctions of the planet with the Sun as observed from Earth
• Mercury’s synodic period is 116 Earth days
Section 16.2
Mercury shown in inferior and superior conjunctions with Earth
Section 16.2
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 16.3
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 16.3
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 16.3
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 16.3
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
• Precession – the slow change of the earth’s rotational axis (now at 23.5o) – see chapter 15
Section 16.3
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 16.3
Foucault Pendulum
The pendulum does not
rotate with reference to
the fixed stars.
Experimental proof of the
Earth’s rotation
Section 16.3
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 16.3
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 16.3
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