Glossary for The Starry Messenger

aether — The special, rarefied stuff of which the stars, sun, moon, and planets are composed and
which fills all the space between the stars, sun, moon, and planets. Aether is opposed
to the four elements (earth, water, air, and fire) of which all earthly objects are
composed. Usually spelled ether,
arc — A portion of the boundary of a circle. 360 degrees equal a full circle. 60 minutes equal 1

degree. 60 seconds equal 1 minute.
earth -- Where most of us are.
ecliptic — The apparent path that the sun follows through the fixed stars as it passes full circle

through the fixed stars.

fixed stars — All the visible stars (except the planets) form a massive constellation and seem to
be a spherical container of the sun, earth, moon, and planets. None of the fixed
stars change either their positions with relation to the other fixed stars or their
distances from the other fixed stars.
great circle — The largest circles on the surface of a sphere. For example, on the earth all

longitudinal circles are great circles, whereas no latitudinal circles (except the
equator) are great circles.
moon — See sun below.

opposition and conjunction — Spatial arrangements of the earth, sun, and a planet when all three

lie in a straight line. Opposition is planet then earth then sun (or
sun then earth then planet). Conjunction is earth then planet then
sun (or earth then sun then planet, or sun then planet then earth, or
planet then sun then earth). Where the earth is in relation to the
other two bodies is what is crucial. Earth in the middle (with
other two bodies on opposite sides) equals opposition. Earth at
the end (with other two bodies together on the same side or
conjoined) equals conjunction.

period -- The time it takes a planet to pass full circle through the fixed stars. The sun takes one
year. The moon takes about twenty-eight days. Jupiter takes twelve years. All the
planets appear to move hi an eastern direction through the fixed stars. By period,
Galileo also means the time it takes the "stars" (moons) of Jupiter to move full circle
around Jupiter.

planets — "Wandering stars," that is, stars that do not remain in fixed positions hi relation to the
other stars, but rather, move about in front of the backdrop of the fixed stars. Mercury,
Venus, Mars, Jupiter, Saturn as well as the moon count as planets for Galileo.
starlets -- Little stars.
sun — If you don't know by now, forget it.

zodiac — A band of fixed stars about 46 degrees wide that completely encircles the earth,
moon, sun, and planets. The sun, moon, and planets appear to move in an eastern
direction through this band and never deviate north or south of this band. All the
planets (but not the sun and moon) occasionally retrograde, that is, for a short tune they
move in a western direction in the zodiac before resuming again their eastern
movement. The line stretching through the center of this circular band is the ecliptic.