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Astronomy Fundamentals

  • A2-13: ELLIPSE DRAWING BOARD

    A2-13
    Demonstrate one method of drawing ellipses
    The ends of a string loop are hooked around two pegs on the board and kept tight by the chalk holder. Moving the string around one complete turn produces an ellipse. This procedure creates the locus of points where R1 + R2 = Constant, the equation for an ellipse. Changing the peg position changes the eccentricity of the ellipse.

    Consider inviting students to make predictions about how the shape of the ellipse will change in response to changing the foci in different ways. This can be related to a variety of mathematical and astronomical phenomena.

    FS2

  • E2-02: MEASUREMENT OF RADIUS OF EARTH

    E2-02
    Demonstrate how the radius of the earth can be measured using trigonometry.

    A disc of radius R with two radial tabs, as shown, is mounted on the optical board and illuminated by a parallel beam of light, as if the earth were being illuminated by the sun. The equatorial tab must have its shadow along the horizontal diameter of the disc. Measure the length b of the upper tab, the length a of its shadow, and the distance S along the surface between the two tabs. By geometry: S/R=a/b, or R=bS/a. Compare the result of this calculation with the direct measurement of the radius R of the disc.

    E2, ofc

    e2-02

  • E2-21: PHASES OF THE MOON

    E2-21
    Show the relationship between the phases of the moon and the relative earth-sun-moon positions.
    With the lecture hall dark, a point source illuminates the globe (the slated sphere from A1 is recommended) from various positions. Phases from crescent to full moon show up very clearly.
    A2, LS1

  • E2-22 UMBRA AND PENUMBRA

    E2-22
    Illustrates shadow umbra and penumbra
    The foam ball casts a shadow of each of the two point sources in the box. The umbra is where the two shadows overlap and the penumbra is where only one source is shadowed.
    E2, LS1

    E2-22A

  • E2-23: UMBRA AND PENUMBRA - EXTENDED SOURCE

    E2-23
    Show umbra and penumbra with an extended source, as in an eclipse.
    Hold the foam ball between the extended source (an incandescent-based television lightbox) and a projection screen (In the lecture halls, use the whiteboard behind the blackboards.). The shadow will consist of three distinct regions: (1) The umbra, in which all of the source is shadowed, is the dark central part. (2) The penumbra, where part of the source is shadowed, is the intermediate band around the umbra. (3) The outer region, where none of the source is shadowed, is the brightest region.
    E2, LS1

  • E2-24: UMBRA AND PENUMBRA - COLOR FILTERS

    E2-24
    Identify the source of penumbra regions.
    Combined red and green filters project nearly white light on a screen. When the foam sphere is inserted between the sources and the screen, the penumbral regions take on the color of the filter through which the light in that region has traveled, because the other color has been blocked by the disc. The umbra, where light from both sources is blocked, is nearly black.
    E2, LS1

    e2-24a

  • E2-31: SOLAR SYSTEM MODEL

    E2-31
    Illustrate the approximate angular disposition of the planets around the sun.
    The model consists of a central sun with radiating arms holding the planets. Positions can be adjusted to conform to reality.
    E2

  • E2-33: RETROGRADE MOTION

    E2-33
    Demonstrate the observation of another planet as seen from the earth.
    Turning the crank on the back of the apparatus rotates the two planets around the sun, with the inner planet rotating at about four times the angular speed of the outer planet. The side of each planet opposite the sun is painted black to simulate a shadow. The rod between the two planets aids in fixing the observational line of sight.
    E2

  • E2-34: BASIC ORRERY (PLANETARIUM)

    E2-34
    Demonstrate the sun-earth-moon spatial relationship and related concepts..
    This device, known as an orrery, illustrates how the earth's rotation causes day and night, how the earth's revolution around the sun and the tilt of its axis causes the seasons, and why the moon has phases.
    E2

  • E2-41: TRANSPARENT CELESTIAL GLOBE

    E2-41
    Illustrate some relationships between the earth, the sun, and certain heavenly bodies
    A transparent globe designed to teach earth-space relationships at the beginning level of astronomy, the celestial globe features a 4" diameter terrestrial globe mounted with a 12" diameter star globe, plus adjustable sun model. Both globes and sun may be easily set to show the positions of the stars and planets for any time and place.
    E2

  • E2-43: ROTATING STAR FIELD

    E2-43
    Show the apparent motion of the night sky.
    The star field is painted onto the plate with its pivot passing through the North star.

  • E2-47: TWINKLING STAR

    E2-47
    Show how air currents cause the "twinkling" of a star.
    A laser beam is directed on a distant wall or screen. When the heater is positioned below the laser beam, hot air convection currents and density changes cause the beam to move continuously, or "twinkle."
    FS1, I0

    e2-47a

  • E2-48: NON-TWINKLING PLANET

    E2-48
    Illustrate why a planet does not "twinkle" like a star.
    A beam expander enlarges the laser beam to a few inches diameter on a distant wall or screen (photograph below). When a heater is placed under the beam, convection currents are readily visible in the large spot of laser light. However, because the spot is large it does not move, or "twinkle." This is contrasted with the direct light from the laser, which moves because of the convection currents from the heater. A star twinkles because it is so small, but because of the finite size of planets as viewed from the earth, planets do not twinkle.
    FS1, I0

    e2-48a