The showcase is a separate “ecosystem” filled with items too old, special or fragile to be handled by untrained hands. This page features the current collection and hopefully is up to date. Some of the items are merely placeholders of little value, but in general look nice and interesting. All the items below are ordered by shelf with a description and the describing text (Dutch texts can be found in the discussion section.)

The top shelf features globes, both old and new. The centerpiece of the shelf is the large lunar globe in the center. This is an incomplete lunar globe.

Dating from around 1960, this globe features the Moon from the side we all know it, but also parts of the side we don't. A large portion of the surface was filled in by the 1959 Russian “Luna 3” probe, which mapped parts of the far side of the Moon. All the newly discovered areas are shown with red letters, while the still unknown region remains empty. [(http://www.curatedobject.us/the_curated_object_/2013/11/exhibitions-chicago-mapping-the-moon-the-adler-planetarium-the-curated-object.html)] (Property of WLS)

The picture on the right shows the images sent back by the Luna 3 probe, upon which this globe is based.

The second shelf is mainly dedicated to navigational instruments such as sextants, clocks and almanacs. These are old instruments and not understood by most, so you can read up on the history and use here. For a short discriptive text about using sextants and quadrants, please look here.

This is a large nautical octant from the 18th century. This was among every seaman’s basic equipment. This octant is especially beautiful because of its ivory scales, something not at all unusual in those times. The arc is divided in 105 degrees and engraved with ‘F.W. Noor. Kjöbenhavn’, denoting the Danish manufacturers. Note the early form thumb screw stop, ivory vernier scale marked from 0 to 20 arc minutes, backsight, and triple sun shades indicative of manufactory soon after 1780. [(http://www.westsea.com/tsg3/octlocker/octcapchart10.html)]

This is a replica of a proper Kelvin & Hughes sextant, from 1917. Sextants like this were often used by seamen to determine their position. This was done by measuring the angle between the Sun and the horizon, and compare this to tabulated values in an almanac. Since this involved staring into the sun for long periods of time, this often blinded sailors!

The small sextant is a replica of a proper Kelvin & Hughes London sextant from 1917. It functions well and has a custom solar shade. It has no historical value, but looks nice. Sextants like this were often used by seamen to determine their position. This was done by measuring the angle between the Sun and the horizon, and compare this to tabulated values in an almanac. Since this involved staring into the sun for long periods of time, this often blinded sailors! [(http://www.auctiva.com/hostedimages/showimage.aspx?gid=1717350&image=706494803&images=706494803,706494801,706494795,706494800,706493454,706494797,706494799,706494804,683114559,706493450,706494978,706494806&formats=0,0,0,0,0,0,0,0,0,0,0,0&format=0)][(http://dispuutkaiser.nl/wiki/doku.php?id=telescopes:antique_sextant)](Property of Alex)

A planimeter is an old analogue device for measuring the areas of any arbitrary 2d shape. It relies on a well-known mathematical result known as Green’s theorem, which is a relationship between the surface of a 2d shape and the boundary of this shape.[(http://en.wikipedia.org/wiki/Planimeter)][(http://www.leinweb.com/snackbar/planimtr/wheatley/s10-2.htm)] This particular model is currently unidentified, but estimated to be from early 20th century.

A nautical almanac is a publication with tabulated values for the positions of a selection of celestial bodies. The almanac specifies for each whole hour of the year the position on the Earth’s surface (in declination and Greenwich hour angle) at which the Sun, Moon, planets and first point of Aries is directly overhead. The positions of 57 selected stars are specified relative to the first point of Aries.

To find the position of a ship or aircraft by celestial navigation, the navigator measures with a sextant the apparent height of a celestial body above the horizon, and notes the time from a marine chronometer. That height is compared with the height predicted for a trial position; the arcminutes of height difference is how many nautical miles the position line is from the trial position.[(http://en.wikipedia.org/wiki/Nautical_almanac)]

A photometer measures the amount of light that hits it. It is in fact a one pixel camera. By putting one in a telescope the luminoscity of various objects can be determined. The large black one was used by Jan Hendrik Oort, discoverer of the Oortcloud and director of the observatory from 1945 to 1970.

These photos were taken with the Astrograph, the telescope in the tower next to the gate. Taking pictures with this telescope could take many hours. The right picture shows the moon, the left shows multiple images of Jupiter and its moons. Jupiter and its moons have been imaged multiple times to study the movement of the moons.

The third shelf is not very thematic, it features everything that does not fit in the other shelves. Bones, meteorites and telescope parts.

[]These cards are punched cards. In the twentieth century they were widely used in the computer industry. They were used both to store data, as was the case at the Old Observatory, and to enter commands, as is the case with these cards. Each command had it's own specific combination of holes.

This mirror comes from a reflector. Reflectors are telescopes that use a lens and a mirror instead of a whole system of lenses. This allows astronomers to make better images with smaller telescopes. The principle was known as early as the 11th century, but a working model was only built in 1673.

Unknown how old this is, but it is a nice instrument that shows the temperature, humidity and barometric pressure. (Property of Alex)

Astrocompasses were used to detect the north. An astrocompass determines this based on the position of the stars rather than a magnetic field, like regular compasses. Because of this it is especially useful near the poles and in places with magnetic fields other than that of the earth, like the metal hulls of ships. It was also used to determine the accuracy of other compasses.

The bottom shelf has all kinds of old instruments which were used by people in the observatory. From calculators to a photon multiplier.

The large magnifying power of a telescope makes it hard to aim. Because of this telescopes have a guide scope. This is a much smaller telescope that magnifies less and is attached to the main telescope. If the guide scope is aimed correctly the main telescope will only need some small adjustments, making it much easier to get a good view of objects. Some telescopes even have multiple guide scopes with different magnifying powers.

Before compact and cheap calculators were introduced around 1980 slide rules like these were used frequently, not only by scientists and engineers but also by high school students. The middle part can be slid with respect to the other parts, which could be utilized to perform multiplications, divisions and even logarithmes. These calculations were inaccurate in comparison to electric calculators, but they were very fast.

This typewriter has cyrillic letters. It was owned by Hendrik van der Hulst when he was involved in international space research projects in the sixties. He presumably for his Russian correspondence. This model was produced from 1937 untill 1960.

This is the Monromatic 8N-213, an electric calculator from 1960. The electric calculator was invented in 1954 as the succesor to the mechanical calculator. It can add, subtract, multiply and divide. It even differentiates between positive and negative numbers. Each column on the keyboard represents a digit.

This Continental Standard is from 1938. It was one of the most popular machines of its time. After the Second World War, however, Continental went bankrupt and these models were no longer made. Typewriters were used between 1860 and 1980. Eventually they were replaced by computers.

The first calculator was built in 1623, but they weren’t sold commercially until 1887. This model comes from a company called Original Odhner and was produced from 1935 to 1945. It uses pinwheels and can add or subtract 10 digit numbers by setting the number and turning the handle. By repeatedly adding or subtracting the same number it can also be used to perform multiplications and divisions. (Property of Alex)