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Homework Help: Tilt of the Earth

  1. Sep 30, 2012 #1
    1. The problem statement, all variables and given/known data

    Suppose the tilt of Earth’s equator relative to its orbit were 177.4◦ (like Venus) instead of
    23.5◦. At what latitudes would the Arctic and Antarctic Circles and the two Tropics be lo-

    2. Relevant equations


    3. The attempt at a solution

    I would like someone to help me make a mental image or reword this for me as this is probably the easiest question on a large astrophysics assignment I have but I am having trouble picturing this and understand how Venus's retrograde motion works.
  2. jcsd
  3. Sep 30, 2012 #2


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    Staff: Mentor

    The latitudes of these great circles are related to the tilt of the planet.

    For example, if the inclination from the vertical is i, then the tropics are at latitudes +/- i. These circles represent the greatest deviation from the equator where the Sun can appear directly overhead; i.e. the circle of greatest altitude of the Sun, occurring on the Solstices.

    The arctic and antarctic circles are the limits where the Sun can be above the horizon or below the horizon for an entire day.

    Draw a circle representing the Earth and draw lines through the center tilted 23.5° to the horizontal (+ and - 23.5°). Their intersection with the circle represents the limits of the Sun's maximal excursion North and South for being directly overhead; those are the Tropical limits.

    Do the same with lines tilted 23.5° from the vertical. These lines intersect the surface at the limits of the arctic circles.

    Now draw a new circle and draw lines with tilts of +/- 177.4° . Note the intersections and compare to those for the Earth's circle.

    The remaining questions are how do you designate North and South poles to name the arctic versus the antarctic circles, and what will be the naming convention for the Tropical latitudes, which were originally astrologically named from an Earth perspective (in which constellations is the Sun when it reaches the solstices?).
  4. Sep 30, 2012 #3
    Thank you for your help, this was really easy to picture and made my point of view much clearer. Have a great day/night :D
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