Download astrolabe - English 381 - Professor Mueller

Little Lewis, my son, I
have prepared a
lesson on the
astrolabe for you,
because I see that you
are interested in
science. The reasons I
have prepared my own
treatise in English on
the subject are as
follows:
1. No one in our region of England thoroughly
understands the astrolabe;
2. I have found mistakes in other manuscripts
about the astrolabe;
3. Your Latin is not quite good enough to be
reading complex material in that language, and
lastly,
4. You are only ten years old, and a simpler treatise
written in plain English will help you
understand the astrolabe better.
My son Lewis, as a philisopher once said,
“he wrappeth him in his frend, that
condescendeth to the rightful preyers of
his frend,” or in other words, “a good
friend helps out his friend” which is what
I am trying to do by giving you this
treatise.
“Don’t be envious of my knowledge of science; all that I have written
here is not my own work, but compiled from other manuscripts. But
considere wel, that I ne usurpe nat to have founde this werk of my labour of olde
Astologiens, and have hit translated in myn English only for thy doctrine; and with
this swerd shal I sleen envye.
The treatise has 5 parts:
1. A general description of the astrolabe
2. How to use it
3. Charts concerning latitude and longitude
4. Charts concerning the movements of celestial bodies
5. A general introduction into the theory of astrology
So far, I have only the first two parts; I will give you the others in time.”
PART I
Here begins the description of your astrolabe:
1. The astrolabe has a hole in it, with which to put your thumb through, for
measuring height, or, as I will from now on call it, “altitude”.
2. The ring can also go through a chain, from which the astrolabe hangs down
from.
3. The astrolabe consists of plates piled on top of each other.
4. A line crosses the astrolabe: the upper part is called the south line or
meridionel, and the lower part is called the north line or the line of midnight.
5. There is also a line running down, creating a cross like
this:
6. The left side is west, and the right side is east.
7. The astrolabe is divided into 90 degrees. Numbers are
engraved in 5 degree increments. Each stroke of the
astrolabe represents a mile, and every degree represents
4 minutes of time. This figure shows the scale:
8. The astrolabe is divided into the
12 zodiac signs. These are divided
into 5 degree increments as well,
but are different than the numbers
on the border; each degree
represents 60 seconds rather than 4
minutes.
9. The astrolabe is also divided into
365 days.
12. Next to the A B C lines,
there is a scale made up of
two squares that is divided
into 12 points. The top part is
called the Umbra Versa and
the bottom part is the Umbra
Recta (or Extensa).
13.The alidade (see photo)
can be used to determine the
sun’s position during the day
or the stars’ positions at night.
14. A pin holds the rete and
plates to the mater. It acts
like the North Pole of the
Astrolabe.
15. The womb side of the Astrolabe into four
quarters by a cross, just like the other side.
16. The womb side is divided exactly the same
way as the other side (see number 7). Chaucer
makes it clear that he has said this twice “Now
have I told the twyes”
17. Under the rete, the plate is engraved with
three circles: Cancer, Aries/Libra, and Capricorn.
These three circles or events are important
because: Cancer is the summer solstice;
Aries/Libra are the equinoxes (where the division
between day and night are the same); and
Capricorn which is the winter solstice.
18. There are concentric circles engraved on
the astrolabe called almuncantars (on
diagram Altitude arcs). The zenith is the
center of the smallest circle and should be
the point directly
above your
head.
19. Azimuths make right angles with the zeniths. They can
be used to find the zenith of the sun or any other star.
20. Twelve divisions under the azimuths indicate planetary
hours.
21. The zodiac plays an important role in using the
astrolabe. Zodia is a Greek word meaning “beasts” in
Latin. Either the sun takes on the characteristics of the
beasts when it enters the signs, or the stars are arranged
like the beasts, or the planets take on the beastly
characteristics when they move through the signs. There
can be other effects felt as the planets move through the
signs (for example, if a hot planet moves through a hot sign
or a cold planet moves through cold sign). Each of the
twelve signs also governs parts of the body (Aries=head,
Taurus=throat, Gemini= arms and armpits, etc).