Instrument: 14th Century European Astrolabe
Plates: 40 – 45 degrees N
Plate replicated: 43 degrees N
To determine the time of day or night:
Begin by measuring the angle of a specific star (or the sun) using the alidade on the back. This piece has two small holes to look through as you hold the astrolabe from a ring attached to the top (if aiming at the sun do not look through the alidade but instead align it as such so that a beam of light passes through both holes onto a surface near you). Once our view is aligned read off the angle of the sun or star on the outer edge.
Flip over the astrolabe and position your star to the correct altitude by rotating the rete. (If measuring the suns angle you have to know the date according to the zodiac and use the eclipse on the rete.) Double check with a compass to determine which side of the projection your star should be. Once positioned you can use the rule to read off the time of day. On this particular astrolabe there are no times displayed but it is marked at 15 degree intervals that correspond to an hour of the day. E and W mark 6am/pm respectively.
For the sun you need to position the correct date on the eclipse with the angle of the sun determined and again use the rule to measure off the time of day.
To determine sunrise and sunset times:
Select your correct date according to the zodiac and line up the corresponding mark on the eclipse with the corresponding side of the horizon line. Left side being East therefore sunrise and the right side being West therefore sunset.