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Next Lecture Blackboard UWS Physics Dept

Observations and the Solar System : Lecture 1

  • Astronomy is an area of science with an ancient history and a very active present.
  • It is an area of science which has challanged humanities self-awareness
  • It is an Observational Science. This is very different from science like Physics and Biology - one must wait until something happens unlike these other sciences where one can carry out experiments. For this reason the course will, initially focus on the observational aspects X

    Observations with the naked eye

    We will start with the most obvious objects in the sky - namely the sun and moon, take a fresh look at the observed patterns these have

    The Sun

    We can draw figures of the suns passage through the sky (looking south) and show how the sun follows a path which changes with the seasons of the year.
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    View South
    The Sun's path-the ECLIPTIC
    The Sun's path tommow is smaller
    In decreases untill the WINTER SOLSTICE
    after which it increases
    until it maximises at the SUMMER SOLSTICE
    and then decreases again..

    Definitions

  • The ecliptic is the path through the sky of the sun.
  • The Winter solstice is the shortest day: equivalently the day where the suns path is the lowest.
  • The Summer Solstice is the longest day
  • The equinoxes are the days of exactly 12 hours duration

    The Moon

    The moon has a passage through the sky, in many ways similar to that of the sun. The moon is found close to the ecliptic at night time - never being more than 5 degrees away from it. ( It swings along its path almost like the sun. However the moons position - measured at midnight say, changes from day to day. Facing south, it is 13.2 degrees further east at midnight each night. X
    View South
    the moon is found within 50 of the ECLIPTIC
    On the following night, at the same time it is found to the east
    with the path around the ecliptic
    and the folowing night
    and the folowing night
    and the folowing night
    and the folowing night
    We discussed how to measure angles using one's hand. A full hand-width was approximately 10 degrees. A finger-tip was about one degrees. You can use this to check that the angular size of the sun and the moon are about 1/2 degree each (be careful with the sun.)

    The Moon has phases

  • Full Moon
  • Waning Gibbeous
  • Quarter Moon
  • Waning Cresent (just visable before sunrise)
  • No Moon/New Moon
  • Waxing Cresent (cresent pointing towards sun beneath horizon)
  • Quarter Moon
  • Waxing Gibbeous
  • Full Moon again
    You can link to a java-script which illustrates this rather well.
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    © Dave Dunbar 2020