Largest stainless steel astrolabe is ready in India. It has 36 cm diameter, 10mm thickness and 8 kilograms weight.
Astrolabe is an ancient scienfic instrument used find the apparent positions of the Sun and
other important stars in the sky for any time of the day or night throughout the
year. It was used both to make observations and to carry out calculations and was the
most widely used scientific instrument in the middle ages and into the early modern
period. An astrolabe can be thought of as a form of computer; a multi function calculator. Its most
common usage were solving of Solving problems of geometry ,Converting between
timekeeping systems , Calculating trigonometric functions , Basic surveying , and
much more concerning astronomy and time keeping, but the full range of its capabilities
is much larger: Alchemists, astronomers, astrologers, and educated individuals were used
astrolabes.
Use of the astrolabe would have been taught in the course of advanced classes in the
natural Siences and mathematics, the way slide rules used to be, and high end calculators are
now.
Most of the surviving astrolabes are constructed of metal, preserved by their higher
value and duability. But there are also several surviving examples from the medieval
period of astrolabes constructed of both paper and wood (and sometimes paper
laminated to wood), so that we can assume that cheap versions where not uncommon.
Basics of Astrolabes
Understanding the various functions of the astrolabe is made easier if you have an
understanding of the concepts behind its design, how they are used in the astrolabe and how the
various parts work:
The Celestial Sphere .
The sky seems to be a hemisphere turned down on us and two hemispherers of day and night can
be imagined as a large sphere with the fixed stars attached to it, with the Earth, stationary
and nonrotating, at the center. The Sun, the Moon, and the planets all had their own
concentric spheres between the Earth and the stars. As the various spheres rotate about the
earth, different parts of the sky would become visible to a viewer standing in a given
spot. Like the Earth itself, this celestial sphere has many fixed landmarks allowing the
observer to find his or her way around:
The Celestial Poles and Equator
At due north, at the point about which the sphere appears to rotate, is Polaris, the
North Star, or Pole Star. This point marks celestial north. Opposite it, invisible to
viewers in the northern
hemisphere, is celestial south. Between these two extremes is a
circle marking the celestial equator. As these all lay directly above their earthbound equivalents,
you can think of these points the way you think of Earth’s north and south poles, and
equator; and just as you can define your position on the Earth using your latitude and
longitude, positions on the celestial sphere can be similarly defined.
The Ecliptic
The most obvious object in the sky is the Sun. As the Earth rotates (or as it would have been
explained in the days when the astrolabe was current technology, as the Sun rotates around
the Earth), the sun rises, moves across the sky from East to West and sets. Over
the course of the year the Sun seems to move across the fixed stars, oscillating from north to
south and back again. This set path in the sky that the sun moves along is known as the ecliptic
and is marked by the zodiac constellations.
The Tropics
As the Sun moves along the ecliptic, it moves toward the north as summer approaches, and back
south as winter comes. The circle marking the northernmost point of the sun's path is
known as the Tropic of Cancer and the southernmost the Tropic of Capricorn.
The Celestial Year
There are 4 fixed events in the year, defined by the sun’s motion along the ecliptic.
The Solstices
The solstices mark the longest and shortest days of the year, these are the dates when the sun is at
its most northerly and southerly limits.
The Equinoxes
The ecliptic intersects the equator, on two days of the year. These dates are the spring and fall
equinoxes. The spring equinox occurs when the sun moves from the southern hemisphere to
the northern; and the reverse is true for the fall equinox.
The Local Sky
In addition to the celestial sphere, the astrolabes function relies on knowledge of the local
sky from the point of view of the user’s location. When you look up at the sky you can see half of
the celestial sphere; the other half being blocked by the ground you are standing on. What part
of the sphere is visible depends on where you are and the time of day and the time of the
year.
The Horizon
The horizon is marked, rather obviously, by the line where the sky meets the ground. Of
course, your local terrain, mountains and such will alter what can actually be seen, but for the
purposes of this manual imagine it as a smooth line all the way round you.
The Zenith and Nadir
The point highest in your local sky (i.e. Directly overhead) is the Zenith; its
opposite point, directly under your feet, is called the Nadir. The horizon then
lies 90 degrees from both.
Almucantars
An almucantar is defined as a line of equal elevation above the horizon. For example:
Imagine a line that lays 15 degrees above your local horizon, all around the sky. That would be the
15degree almucantar.
The Meridian
The last major landmark we will concern ourselves with is the meridian . This is an imaginary line
in the sky, passing from the north celestial pole to the south celestial pole,
and
passing directly over your head (zenith). This line marks local noon, the sun's highest point
above the horizon for any given day. Picture it as a line in the sky running from due north to due
south directly overhead.
The Projections If you have done any work with maps, you will be familiar with the
concept of projections. The Earth is a sphere; so creating a flat map of the curved
surface involves projecting that Sphere onto a flat surface. This is why, on some maps, the
continents appear very distorte near the poles. The astrolabe is based on what is known as
the planispheric projection. In a planispheric projection, a spherical object is projected onto
a plane surface by placing the origin of the projection at one pole of the sphere and
projecting the points of the sphere onto a plane surface placed through its equator. The
astrolabe is based on what is known as the planispheric projection. In a planispheric projection, a
spherical object is projected onto a plane surface by placing the origin of the projection at one
pole of the sphere and projecting the points of the sphere onto a plane surface
placed through its equator. , With its projection of the local sky. The top half of the plate
contains the circular grid that is the projection of the local sky from the horizon (the bottom
most curve of the grid) to the zenith (the cross at the center of the smallest circle). Again,
the outermost circumference of the plate is the projection of the Tropic of Capricorn, and its
center marks the projection of the celestial pole. If you examine these projections, you will
notice that in both cases the projection is oriented the same, with the north celestial pole projecting
as a point in the exact center of the projection. This allows us to overlay the projections, the
celestial sphere over the local sky, and pivot it on the celestial pole By rotating the rete the user
can then display the local view of the sky for any combination of time and day of the year.
The Parts of the Astrolabe
The Mater
The Mater is the main fixed part of the astrolabe; all the other parts connect to it. Permanently fixed
to it are the Throne and the Limb.
The Throne
The Throne is attached to the top of the mater, and provides a means of suspending the
astrolabe to take sightings. In use, a ring or cord would be attached to the throne, allowing it
to hang freely and so allow measuring angles from the horizon accurately. Depending
on the time, place and use of the maker, the throne might be anything from a simple
Astrolabe is an ancient scienfic instrument used find the apparent positions of the Sun and
other important stars in the sky for any time of the day or night throughout the
year. It was used both to make observations and to carry out calculations and was the
most widely used scientific instrument in the middle ages and into the early modern
period. An astrolabe can be thought of as a form of computer; a multi function calculator. Its most
common usage were solving of Solving problems of geometry ,Converting between
timekeeping systems , Calculating trigonometric functions , Basic surveying , and
much more concerning astronomy and time keeping, but the full range of its capabilities
is much larger: Alchemists, astronomers, astrologers, and educated individuals were used
astrolabes.
Use of the astrolabe would have been taught in the course of advanced classes in the
natural Siences and mathematics, the way slide rules used to be, and high end calculators are
now.
Most of the surviving astrolabes are constructed of metal, preserved by their higher
value and duability. But there are also several surviving examples from the medieval
period of astrolabes constructed of both paper and wood (and sometimes paper
laminated to wood), so that we can assume that cheap versions where not uncommon.
Basics of Astrolabes
Understanding the various functions of the astrolabe is made easier if you have an
understanding of the concepts behind its design, how they are used in the astrolabe and how the
various parts work:
The Celestial Sphere .
The sky seems to be a hemisphere turned down on us and two hemispherers of day and night can
be imagined as a large sphere with the fixed stars attached to it, with the Earth, stationary
and nonrotating, at the center. The Sun, the Moon, and the planets all had their own
concentric spheres between the Earth and the stars. As the various spheres rotate about the
earth, different parts of the sky would become visible to a viewer standing in a given
spot. Like the Earth itself, this celestial sphere has many fixed landmarks allowing the
observer to find his or her way around:
The Celestial Poles and Equator
At due north, at the point about which the sphere appears to rotate, is Polaris, the
North Star, or Pole Star. This point marks celestial north. Opposite it, invisible to
viewers in the northern
hemisphere, is celestial south. Between these two extremes is a
circle marking the celestial equator. As these all lay directly above their earthbound equivalents,
you can think of these points the way you think of Earth’s north and south poles, and
equator; and just as you can define your position on the Earth using your latitude and
longitude, positions on the celestial sphere can be similarly defined.
The Ecliptic
The most obvious object in the sky is the Sun. As the Earth rotates (or as it would have been
explained in the days when the astrolabe was current technology, as the Sun rotates around
the Earth), the sun rises, moves across the sky from East to West and sets. Over
the course of the year the Sun seems to move across the fixed stars, oscillating from north to
south and back again. This set path in the sky that the sun moves along is known as the ecliptic
and is marked by the zodiac constellations.
The Tropics
As the Sun moves along the ecliptic, it moves toward the north as summer approaches, and back
south as winter comes. The circle marking the northernmost point of the sun's path is
known as the Tropic of Cancer and the southernmost the Tropic of Capricorn.
The Celestial Year
There are 4 fixed events in the year, defined by the sun’s motion along the ecliptic.
The Solstices
The solstices mark the longest and shortest days of the year, these are the dates when the sun is at
its most northerly and southerly limits.
The Equinoxes
The ecliptic intersects the equator, on two days of the year. These dates are the spring and fall
equinoxes. The spring equinox occurs when the sun moves from the southern hemisphere to
the northern; and the reverse is true for the fall equinox.
The Local Sky
In addition to the celestial sphere, the astrolabes function relies on knowledge of the local
sky from the point of view of the user’s location. When you look up at the sky you can see half of
the celestial sphere; the other half being blocked by the ground you are standing on. What part
of the sphere is visible depends on where you are and the time of day and the time of the
year.
The Horizon
The horizon is marked, rather obviously, by the line where the sky meets the ground. Of
course, your local terrain, mountains and such will alter what can actually be seen, but for the
purposes of this manual imagine it as a smooth line all the way round you.
The Zenith and Nadir
The point highest in your local sky (i.e. Directly overhead) is the Zenith; its
opposite point, directly under your feet, is called the Nadir. The horizon then
lies 90 degrees from both.
Almucantars
An almucantar is defined as a line of equal elevation above the horizon. For example:
Imagine a line that lays 15 degrees above your local horizon, all around the sky. That would be the
15degree almucantar.
The Meridian
The last major landmark we will concern ourselves with is the meridian . This is an imaginary line
in the sky, passing from the north celestial pole to the south celestial pole,
and
passing directly over your head (zenith). This line marks local noon, the sun's highest point
above the horizon for any given day. Picture it as a line in the sky running from due north to due
south directly overhead.
The Projections If you have done any work with maps, you will be familiar with the
concept of projections. The Earth is a sphere; so creating a flat map of the curved
surface involves projecting that Sphere onto a flat surface. This is why, on some maps, the
continents appear very distorte near the poles. The astrolabe is based on what is known as
the planispheric projection. In a planispheric projection, a spherical object is projected onto
a plane surface by placing the origin of the projection at one pole of the sphere and
projecting the points of the sphere onto a plane surface placed through its equator. The
astrolabe is based on what is known as the planispheric projection. In a planispheric projection, a
spherical object is projected onto a plane surface by placing the origin of the projection at one
pole of the sphere and projecting the points of the sphere onto a plane surface
placed through its equator. , With its projection of the local sky. The top half of the plate
contains the circular grid that is the projection of the local sky from the horizon (the bottom
most curve of the grid) to the zenith (the cross at the center of the smallest circle). Again,
the outermost circumference of the plate is the projection of the Tropic of Capricorn, and its
center marks the projection of the celestial pole. If you examine these projections, you will
notice that in both cases the projection is oriented the same, with the north celestial pole projecting
as a point in the exact center of the projection. This allows us to overlay the projections, the
celestial sphere over the local sky, and pivot it on the celestial pole By rotating the rete the user
can then display the local view of the sky for any combination of time and day of the year.
The Parts of the Astrolabe
The Mater
The Mater is the main fixed part of the astrolabe; all the other parts connect to it. Permanently fixed
to it are the Throne and the Limb.
The Throne
The Throne is attached to the top of the mater, and provides a means of suspending the
astrolabe to take sightings. In use, a ring or cord would be attached to the throne, allowing it
to hang freely and so allow measuring angles from the horizon accurately. Depending
on the time, place and use of the maker, the throne might be anything from a simple