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======= Antique Sextant =======
{{ :telescopes:sextant.jpg?200|}} This is a cheap, but functional replica of an antique sextant. It has little to do with the history of the building, besides the fact that there used to be a marine instrument testing facility in the old observatory building when Kaiser first opened it. Here they built, tested and fixed many instruments used for naval purposes. And since most of those relied on navigation by sky, astronomy was not too weird of a combination.  

It is quite usable for tours and looks real enough to impress the tour group. As it is another fancy looking doohickey.  

The sextant can be found in the "KaiserHok". 
===== Short facts =====
  * Replica of a [[http://en.wikipedia.org/wiki/Kelvin_Hughes|Kelvin & Hughes]] London sextant from 1917
  * It is not an original

===== What does it do? ===== 
A sextant is an instrument used to measure the angle between any two visible objects. Its primary use is to determine the angle between a celestial object and the horizon which is known as the object's altitude. Using this measurement is known as sighting the object, shooting the object, or taking a sight and it is an essential part of celestial navigation. The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart. Common uses of the sextant include sighting the sun at solar noon and sighting Polaris at night (in the Northern Hemisphere), to find one's latitude. Sighting the height of a landmark can give a measure of distance off and, held horizontally, a sextant can measure angles between objects for a position on a chart. A sextant can also be used to measure the lunar distance between the moon and another celestial object (e.g., star, planet) in order to determine Greenwich time which is important because it can then be used to determine the longitude.

The scale of a sextant has a length of ⅙ of a turn (60°); hence the sextant's name (sextāns, -antis is the Latin word for "one sixth"). An octant is a similar device with a shorter scale (⅛ turn, or 45°), where as a quintant (⅕ turn, or 72°) and a quadrant (¼ turn, or 90°) have longer scales.

Sir Isaac Newton (1643–1727) invented the principle of the doubly reflecting navigation instrument (a reflecting quadrant—see Octant (instrument)), but never published it. Two men independently developed the octant around 1730: John Hadley (1682–1744), an English mathematician, and Thomas Godfrey (1704–1749), a glazier in Philadelphia. John Bird made the first sextant in 1757. The octant and later the sextant, replaced the Davis quadrant as the main instrument for navigation. From [(http://en.wikipedia.org/wiki/Sextant)].


===== Using a Sextant =====
As read above, a sextant can be used to measure the angle between various things. Most often this is the sun and the horizon, but it can also be other things like the moon and a star, etc. Various very detailed charts exist for these measurements, soon one will appear in the ostrw.

Here you can see how a basic measurement is made by aligning two objects. (In this case the horizon and the Sun.)
{{ :telescopes:using_sextant.gif |}}\\
Here you can see our sextant in action, measuring the angle between [[User:Alex|Alex']] desk lamp. Which turned out to be 50 degrees at the arbitrary distance from the lamp. **Remember:** These measurements only have meaning if you know the distance or assume that the objects are at the same distance. (like things in space.).)\\
So you look at your two reference points (light bulb and lamp foot), aim at the foot and move the sextant arm until you also see the bulb. The angle of the arm is then the angle between the two spots. 
{{:telescopes:sextant_image.jpg?200|}}{{:telescopes:sextant_measure.jpg?200|}}{{ :telescopes:sextant_lamp.jpg?200 |}}\\

{{gallery> telescopes}} 
In your scope this will look very much like the example animation, only a little less perfect.


==== Safety ====
{{ :telescopes:sextant_filters.jpg?200|}}It is very important to remember that this is a replica, so not really made to be used. This means that this sextant has __**not**__ been subjected to any safety test. 

This is not bad if you are looking at stars, planets or the moon. But keep in mind that the Sun is very bright and can permanently blind you. 

This said, it has been modded to be usable for the Sun by adding a special solar filter to the filter flaps. 
As can be seen in the picture, the sextant has 3 filters for the top mirror and 3 for the bottom one. When looking at the Sun, there are two options. Either use the outer two when it is cloudy or just the most inner one when it is bright. __**ALWAYS**__ use the first filter when looking at a unclouded Sun. This filter is made from special solar paper which is also used in eclipse glasses. Also always check if the tape/filter are still in place before using. 

You use the filter by flipping it down in front of your eyepiece. Always check on a lamp if it is in the right position.

If all this is heeded, then the sextant is a safe and fun toy.

=== Steps ===
Always follow these steps before use to look at Sun.
  * Check if square filters are still attached. (Don't touch them.)
  * Set the arm to 0 degrees and look at a light. It should be visible in both scopes (if you don't use the frontal filter).
  * Check if the eyepiece is not loose. It tends to fall out sometimes.
  * Stand in front of the Sun, aiming it at something directly below it. 
  * Check if correct filters are place. 
  * Start sliding the arm from 0 degrees to a higher angle until the Sun appears in the second view. (Don't go beyond this point, as some time later there is a secondary reflection off the surface of the filter which will not be filtered!
  * Note the sextant angle, and draw conclusions about position.