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When sighting celestial bodies on the horizon, you are pretty much limited
to the sun, and the moon. In ideal conditions, the planets (except Saturn)
and the star Sirius can be used. But for all other bodies, absorption of
light in the atmosphere means that they are only visible once they have
reached a certain altitude above the horizon. A rule of thumb is that in
ideal conditions, the celestial body only becomes visible once it has
attained an altitude which in degrees is equal to its magnitude. (This is
for observations using the un-aided eye)

For celestial navigation without any instruments at all, the Polynesian
canoe Hokule'a (Arcturus) has made a number of Hawaii-Tahiti round trips
and one to 16,000 mile trip to New Zealand and back using traditional
methods, based largely on the use of zenith stars.

I recall an article in Ocean Navigator back in 1985 in which Marvin Creamer
described his circumnavigation of the world in his yacht Globe Star,
without any instruments at all. More details at
http://www.globestar.org/feat.htm Creamer also used zenith stars as his
principal means of navigation.

Geoffrey Kolbe


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