Part I: The Sky, an Introduction - Basic Concepts

• General scales of the Universe:
  • the astronomical unit
  • solar system distances and sizes
  • the light year.
• Coordinate Systems
  • The Horizon system of coordinates (Altitude/Azimuth).
    • advantages and disadvantages of such a Local Coordinate system
  • The concept of the Latitude and Longitude to measure positions on the Earth.
    • The Prime Meridian (Greenwich Meridian) at Longitude =0 degrees.
  • Celestial Coordinates:
    • Right Ascension (Celestial Longitude) and Declination (Celestial Latitude).
    • Celestial North and South poles as extensions of the Earths North and South Poles
    • The Celestial Equator
    • Zero point of Right Ascension = Vernal Equinox.
    • Division of celestial longitude into Hours instead of degrees (24hrs=360 degrees).
    • Right Ascension INCREASES to the East from the Vernal Equinox.
    • The Autumnal Equinox at RA=12 hrs, Dec=0 degs.
  • the altitude of the Celestial Poles and the highest point on the Celestial Equator from any latitude on the Earth.

The Sun and its Path on the Sky

• the Ecliptic Plane (the plane containing the orbit of the Earth around the Sun.
• The Seasons
  • tilt of the Earth away from the vertical relative to the Ecliptic (The angle of Obliquity= 23.5 degrees for Earth).
  • effect of this tilt on the amount of sunlight reaching various part of the Earth at various times of the year.
  • reasons why the its usually much colder in the winter than summer at mid-northern latitudes of the Earth.
• the apparent path of the Sun on the Celestial sphere.
  • passes through the Vernal Equinox moving North (in Spring; March 20/21) at RA=0 Dec=0,
  • reaches Dec=23.5 deg and RA=6hrs on June 20/21(Summer Solstice),
  • back to the Equator (Dec=0) at RA=12hrs on Sept 20/21
  • most southerly Dec=-23.5 deg at RA=18hrs (Winter Solstice).
  • maximum altitude at noon at various times of the year.
    • (Should be able to draw a meridian diagram for the Sun as it transits the local meridian)

The Moon and its Phases

• Synodic and Sidereal Month and reason why one is longer than the other.
• Phases of the moon; inverse relationship of the Earth's phases as seen from the Moon.
• relationship between the phases of the moon, the time of day and the appearance of the moon in the sky.
• the moon always has the same face towards the Earth
• The tilt of the Moon's orbit relative to the Ecliptic (Earth-Sun plane).
• Where is the _____ moon in the sky at ____ time of day?

Path of Moon on Sky; Eclipses

• path of the Moon on the celestial sphere and its relationship to the path of the Sun.
• crossing points of the Moon's orbit and the Sun's path on the sky (nodes)
• significance of the Lunar nodes for the occurrence of Eclipses
• Properties of shadows of planetary bodies
• definition of total, partial and annular solar eclipses
• frequency and visibility of lunar and solar eclipses
• Lunar eclipses and their relationship to solar eclipses

Early Ideas

• Ancient monumental calendars (Mayans, Stonhenge, etc.)
• Ancient Greeks
• Copernicus and the Sun centered universe.
• Tycho Brahe and Kepler
• Galileo - telescope observations and experiments with gravity.
• Kepler's law's of planetary motion.
  • 1st Law of Ellipses,
  • 2nd Law of Areas (and relative speed in orbit)
  • 3rd Law of Periods (p*p = a*a*a).
  • Concept of eccentricity (e) and semi-major axis of ellipse.
  • Physical picture of an elliptical orbit.

Newton and Gravity and Newton's Laws of Motion

• Sir Isaac Newton
• Newtonian Concept of Gravity
  • Gravity as a central force
  • Newton's 3 laws of motion.
  • The motion of Moon - as a falling body
  • Newton's explanation of Kepler's Laws in terms of a theoretical model of gravity.
• Orbital mechanics and interplanetary orbits:
  • how to get to Mars via a transfer orbit.
  • Gravity assist to the outer planets.