From: m.driussi@genie.com
Subject: (urth) How big the Ship?
Date: Wed, 31 Mar 99 02:05:00 GMT

Today I finally found reason to try and calculate the size of the
ship "Tzadkiel" by way of answering the question: if the miracle
eclipse of the Sun by Apu Punchau was caused by the Ship's sails,
then how big would it have to be, and how close to Earth, to cause a
total eclipse?

=Angular Diameter=
The angular diameter of both Sun and Moon is around one-half a
degree. The formula

S = 57.3 x D/R

where D is diameter and R is distance from Earth.

Since the Ship is assumed to be in LEO (Low Earth Orbit), and LEO
ranges from 150 to 2000 km, I just plugged in values to see what
would happen.  I also converted the diameter into leagues, since the
league is the unit Severian uses for very big objects (wall of
Nessus, the cliff in the mountains, etc.).

ORBIT      SAIL DIAMETER       DIAMETER IN LEAGUES
 150 km     1.36 km             0.28
 300 km     2.71 km             0.56
 500 km     4.52 km             0.93
1000 km     9.04 km             1.87
2000 km    18.08 km             3.74

These sail diameters are all quite reasonable--in fact, by standards
of solar sails, they are very modest, since solar sail designs range
in diameter from 2 km to 400 km.

(FWIW, a sail diameter of 400 km can cause total eclipse at an orbit
of 44,235 km.)

=mantis=

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