Astronomy: The Instruments that Made it Possible to Understand the Universe

Musée des arts et métiers

From Antiquity to the age of modern science, man has observed and analyzed the stars to measure and understand the universe. The Musée des Arts et Métiers preserves several tools in its collection of scientific instruments that have marked the history and practice of astronomy. Prestigious objects that are often exceptionally intricate, also bear witness to the fascinating adventure that unites man and the Heavens.
The Astrolabe
The astrolabe is a calculation and pedagogical tool of Greek origin (2nd century BC). It made it possible to solve astronomic problems without any calculations. It identified, for example, the time that the the sun or the stars would rise or set, and the sun's height at its highest point above the horizon, etc.

From the 9th century onward, the astrolabe was
commonly used by Arab-Persian astronomers,
mainly to accurately determine
the precise time to pray.

It was also an instrument that was favored
by astrologers throughout the Middle Ages.
The astrolabe's popularity only started to decline in the West
in the 17th century.

The astrolabe of Arsenius (1530-
1580) exhibited at the Musée des Arts et Métiers
is extraordinary due its
size.

The diameter of the element called the mater (the receptacle)
measures almost 12 inches in diameter.

Here the rete (the movable openwork part that
joins the stars and the sun) is
divided into months with the signs of
the zodiac and it has 43 stars.

An alidade with vanes (a movable ruler
for taking precise measurements)
sits atop the device. There was no doubt
that this instrument was
destined to be used in astronomy.

The Sundial
The sundial dates back to early antiquity when it was a particularly prestigious instrument. This instrument, which has constantly evolved over the centuries, both in its form, its precision and its uses, was mainly intended to indicate solar time. It can also give the dates of the solstices and equinoxes.

From the 17th century, it was used to regulate
the clocks, particularly
when it was simplified to only indicate
midday (the meridian).

During this period, several
varieties of luxury sundials
were developed, just like
this portable sundial made of
ivory.

The dial of Benjamin Scott (1688-
1751) dating from 1713, exhibited
at the Musée des Arts et Métiers, is
distinctive in that it combines two
sundials on a single
face.

One of the benefits of the double dial
was that it was easy to orientate
the device in the true North-
South direction, simply by
rotating it. It functions as a
sort of a compass.

The Sextant
Invented in the 18th century by John Hadley (1682-1744), this instrument makes it possible to measure, very precisely, the height of a star above the horizon, most notably the sun.

It is a 60° sector
equipped with a telescopic sight and
two mirrors. One of these mirrors is adjustable.

By taking at least two height measurements
and doing a calculation,
you can obtain geographical coordinates of your location
(longitude and latitude). Provided that
you have a correctly
set watch.

So in a way the sextant is therefore
an ancestor of the GPS. It was essential for
maritime navigation and it
still is to this day.

French navigators La Pérouse
(1741–1788) and Bougainville
(1729–1811) are among the
most renowned users of this
instrument.

Galileo's Telescope
The idea of combining lenses to lengthen man's viewpoint dates back to 1589. The telescope is undoubtedly an empirically developed Dutch invention. From 1608 it was sold at the Frankfurt Fair.

Galileo perfected the instrument
in the summer of 1609, even though
he didn't understand how
its optics worked.

The discoveries he made with his telescope at the end of that year were published in 1610 in the "Sidereus Nuncius." They turned the world of astronomy upside down.

The four moons orbiting the planet Jupiter were undoubtedly his greatest discovery

Galileo estimated that his telescope magnified 20 times. The magnification effect depends on the diameter of the lens. The largest preserved telescopes in France are in the observatories in Meudon (83 cm) and Nice (76 cm).

Borda's Repeating Circle
The repeating circle, invented by Borda (1733–1799), is a graduated circle supported on a base which can be pointed in any direction. It is an improved version of the theodolite (an instrument used for measuring angles).

It was used to measure an angle by taking repeated measurements and it was used initially for geodesic calculations then later in astronomy.

It is equipped with two telescopes with reticle eyepieces used to aim at the sides of the angle to be measured.

Most famously, Borda's repeating circle was used by the
astronomers Delambre and Méchain in the 18th century, when they were measuring the meridian of Paris to develop the standard measurement of a meter.

The Orrery
The first orreries were mechanical instruments used for demonstration purposes. They were common in England from the 18th century. They made it possible to show students and the public the revolution of the planets around the sun, taking into account the specific orbital period of each planet.

Very often they could also show the planets' rotation on their own axis as well as the rotation of their natural satellites. The earth-moon system was particularly well demonstrated.

Many orreries were equipped with a manually operated gear system although some were equipped with a clock system.

The collection of scientific instruments on show at the Musée des Arts et Métiers makes it possible to retrace certain major advances in astronomy research. Like the universe it seeks to study, astronomy offers infinite possibilities, from amateur practices to the advanced major technologies that define space exploration.
Credits: Story

Author: Denis Savoie, Scientific Advisor at the Musée des Arts et Métiers.

© Images:
Photo library of the Musée des Arts et Métiers
Conservatoire numérique des Arts et Métiers (CNUM)
LIFE magazine
Rijksmuseum
Museo Galileo

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
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