The Elusive Planet of Twilight

  • Richard Baum
  • William Sheehan


The quest for Vulcan begins in the study of the wayward movements of the planets, and so, in a real sense, in the myth and superstition of prehistory when vigilant watchers of the night sky first recognized the wandering stars (planetae in Greek). What were these moving lights? What purpose did they serve? How were they able to move with such precision across the starry heavens?


Apparent Movement Planetary Motion Parish Church Rewarding Object Lick Observatory 
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Notes and References

  1. 1.
    E. M. Antoniadi, The Planet Mercury; trans. Patrick Moore (Devon: Keith Reid, 1974), pp. 9–11. For the reference to Mercury the elusive, Antoniadi cites the authority of Proclus Diadochus; for Mercury the nimble one, Apuleius.Google Scholar
  2. 2.
    Owen Gingerich, “Ptolemy and the Maverick Motion of Mercury,” Sky and Telescope 66, 12 (1983).ADSGoogle Scholar
  3. 3.
    Copernicus, “On the Revolutions of the Heavenly Spheres,” Book V, sec. 29.Google Scholar
  4. 4.
    This is conventionally measured from a fixed point in space known as the first point of Aries, 7, where the ecliptic cuts the equator going from south to north.Google Scholar
  5. 5.
    The ascending node is the point where the planet crosses the ecliptic traveling north; the descending node is where the planet crosses the ecliptic traveling south.Google Scholar
  6. 6.
    To give an example, for Mars Kepler derived the following elements: the semi-major axis a = 1.5264 AU; eccentricity, e = 0.0926; longitude of perihelion, inclination, i = 1° 50′ 25”; longitude Of perihelion, ῶ = 328° 48′ 55”; and longitude of ascending node, Ω = 46° 46½′.Google Scholar
  7. 7.
    For the significance of the observation see Albert Van Helden, “The Importance of the Transit of Mercury of 1631,” Journal for the History of Astronomy 7, 1–10 (1976), andMathSciNetADSGoogle Scholar
  8. 7a.
    Robert Grant, History of Physical Astronomy from the Earliest Ages to the Middle of the Nineteenth Century (London: Henry G. Bohn, 1852), pp. 415–417.Google Scholar
  9. 8.
    P. Humbert, L’Oeuvre astronomique de Gassendi (Paris, 1936), 23.Google Scholar

Copyright information

© Richard Baum and William Sheehan 1997

Authors and Affiliations

  • Richard Baum
  • William Sheehan

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