Lecture 2: Sunrise and Sunset: Apparent Solar Motion

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    • Date: September 1, 1994
    Reading Assignment: pp. 10-13

    Description : Global coordinate systems, the celestial sphere, rotation and revolution of Earth.

    Objectives

  • Understand the differences between Right Ascension, Declination, altitude, and azimuth.
  • Be able to identify the North Celestial Pole, Zenith, and the Celestial Equator.
  • Understand the differences between rotation and revolution.
  • Be able to distinguish diurnal and annual solar motion.
  • Distinguish between solar and sidereal days.
  • Understand how annular motion affects the seasons.

    • Lecture Outline

    Slide # 1: Lecture 2: Sunrise and Sunset: Apparent Solar Motion

    Slide # 2: Review of Lecture 1
  • Class Policies
  • Units of Measurement
  • Powers of 10
  • Global, Local, and Geographic Coordinates
  • Constellations and the Celestial Sphere
  • Altitude and Azimuth
    • Slide # 3: Lecture 2
  • Celestial Coordinate Systems
  • Local- Altitude and Azimuth
  • Global - Right Ascension and Declination
  • Motion of the Earth
  • Apparent Motions in the Sky
  • Diurnal Motion
  • Rotation of the Earth
  • Annual Motion
  • Seasons
  • Solar and Sidereal Days
    • Slide # 4: Three Basic Ways of Locating Something on Earth
  • Geographic
  • City, State, Country, Continent
  • Local Coordinate System
  • 15 miles to the East
  • Global Coordinate System
  • Latitude and Longitude
    • Slide # 5: There are also three main ways of locating something in the sky.
  • Geographic
  • Star (or object), Constellation
  • Local Coordinate System
  • Altitude and Azimuth
  • Global Coordinate System
  • Right Ascension and Declination
    • Slide # 6: A Local Coordinate System
  • The Point Directly Over the Head of the Observer is Called the Zenith
  • The Circle 90 Degrees from the Zenith is Called the Horizon
  • You cannot see Celestial Objects when they are Below the Horizon
    • Slide # 7: The Position of Every Object Can Be Measured Using Two Angles
  • Azimuth - The Angular Distance from the North (Measured to the East)
  • Altitude - The Angular Distance from the Horizon
  • Above the Horizon is Positive
  • Below the Horizon Is Negative
    • Slide # 8: Altitude Slide # 9: Azimuth Slide # 10: A Celestial Coordinate System
  • The North Celestial Pole is the point directly above the North Pole
  • The South Celestial Pole is the point directly above the South Pole
  • The Celestial Equator is the Circle Directly Above the Equator
    • Slide # 11: A Celestial Coordinate System Slide # 12: Measuring Positions on Earth
  • Two Angular Measurements are Used to Determine Position on Earth
  • Latitude - Angular Distance North of the Equator
  • Longitude - Angular Distance East of Greenwich England
    • Slide # 13: Latitude and Longitude
  • Insert earth diagram here
    • Slide # 14: Measuring Positions on the Celestial Sphere
  • Two Angular Measurements are Used to Determine Position on the Celestial Spher
  • Declination - Angular Distance North of the Celestial Equator
  • Similar to Latitude
  • Right Ascension - Angular Distance East of the Vernal Equinox
  • Simliar to Longitude
    • Slide # 15: Declination Slide # 16: Right Ascension Slide # 17: Right Ascension and Declination
  • A grid which is fixed to the background stars.
  • Similar to Latitude and Longitude on Earth
  • A Global Coordinate System
    • Slide # 18: Right Ascension and Declination
  • The Earth's Rotation Causes the Stars to Move Across the Sky
  • Right Ascension and Declination Of A Star Do Not Change Due to the Earth's Rot
    • Slide # 19: Motion of the Earth
  • Rotation
  • The Earth is Spinning on its Axis
  • Revolution
  • The Earth Orbits Around the Sun
    • Slide # 20: Rotation
  • The Celestial Sphere Does Not Move
  • The Earth Rotates Inside the Celestial Sphere
    • Slide # 21: Revolution
  • The Earth Revolves Around the Sun
    • Slide # 22: Motion in the Sky
  • Diurnal Motion
  • The Sky Appears to Change due to the Earth's Rotation
  • One Rotation Takes One Day
  • Annual Motion
  • The Sky Appears to Change due to the Earth's Revolution
  • One Orbit (or Revolution) Takes One Year
    • Slide # 23: Diurnal Motion
  • Apparent Motion Due to the Rotation of the Earth
  • Right Ascension and Declination of the Objects Do NOT Change
  • Altitude and Azimuth Change
  • Some Examples
  • Sunrise, sunset
  • Motion of the stars across the sky
    • Slide # 24: Diurnal Motion
  • The Observer SEES the Stars Move the Same Way Every Day
  • Different Observers SEE Different Motion
  • This Motion is from the ROTATION OF EARTH
    • Slide # 25: Diurnal Motion is Different for Different Observers
  • Diurnal Motion Depends on the Rotation of Earth
  • Observers at Different Latitudes See Different Diurnal Motion
    • Slide # 26: A View from the North Pole Slide # 27: A View from the North Pole Slide # 28: A View from the Equator Slide # 29: A View from the Equator
  • The Celestial Equator is Directly Over the Equator
  • For an Observer on the Equator, the Celestial Equator is Directly Above the Ob
    • Slide # 30: Between the Equator and the North Pole
  • Neither the Celestial Equator or the North Celestial Pole is Overhead
  • Stars Rotate Around the North Celestial Pole
    • Slide # 31: Between the Equator and the North Pole Slide # 32: Annual Motion
  • Changes Caused by the Revolution of Earth Around the Sun
  • Follows a Yearly Cycle
  • Responsible for Seasons
    • Slide # 33: Annual Motion Slide # 34: The Ecliptic
  • The Sun, Planets, and Moon are found near the Ecliptic
    • Slide # 35: Sidereal and Solar Days
  • A Day is One Rotation of the Earth
  • A Solar Days is One Rotation of the Earth Measure By the Position of the Sun
  • A Sidereal Day is One Rotation of the Earth Measured By the Positions of the S
    • Slide # 36: Sidereal and Solar Days Slide # 37: The Earth Orbits Around the Sun Slide # 38: It Appears the the Sun Follows a Set Path Through the Constellations Slide # 39: Annual Motion - A Complication
  • The Earth's Revolution Axis is NOT Aligned with Its Rotation Axis
  • The Difference in the Tilts is 23.5 Degrees
  • Because of this Tilt, the Declination of the Sun Changes from -23.5 South to 2
    • Slide # 40: Annual Motion Slide # 41: Seasons
  • The Changes in the Sun's Declination Causes Seasons
  • There are 4 Important Dates During the Year Related to Annual Motion
  • The Summer Solstice
  • The Winter Solstice
  • The Vernal Equinox
  • The Autumnal Equinox
    • Slide # 42: The Summer Solstice
  • The Sun Reaches It's Maximum Angular Distance North of the Celestial Equator
  • Occurs on the First Day of Summer (About June 22)
    • Slide # 43: The Winter Solstice
  • The Sun Reaches It's Maximum Angular Distance South of the Celestial Equator
  • Occurs on the First Day of Winter (About December 22)
    • Slide # 44: The Vernal Equinox
  • The Sun Crosses the Celestial Equator Travelling Northward
  • The First Day of Spring (About March 22)
    • Slide # 45: The Autumnal Equinox
  • The Sun Crosses the Celestial Equator Travelling Southward
  • The First Day of Autumn (About Sept 23)
    • Slide # 46: The Seasons Slide # 47: Why is it Cold in Winter?
  • On December 21, the Sun is at a Declination of -23.5 Degrees
  • How does this Influence the Climate?
    • Slide # 48: Lecture 2 : A Review
  • Celestial Coordinate Systems
  • Local- Altitude and Azimuth
  • Global - Right Ascension and Declination
  • Motion of the Earth
  • Apparent Motions in the Sky
  • Diurnal Motion
  • Rotation of the Earth
  • Annual Motion
  • Seasons
  • Solar and Sidereal Days
    • Slide # 49: Lecture 3: It's Just a Phase I'm Going Through- The Moon
  • Lunar Motion
  • Phases
  • Eclipses