AMTG Virtual Cross Staff & Back Staff 2008 GC

Help to guide you to another cache. This is a depiction of a device that was used to guide those in the past to their "caches". I love it and want to share it with other cachers.

Large coin with lots of heft. 2 inches 4 mm thick antique bronze.  Available in other metal colors.  Unusual shape due to the unusual rim work. The front has very nice background texture and rim design. The 3-D work in the medallion is life like, bold and very detailed. It shows small details as well as having raised images. It shows early sailers using a back staf for navigation. The medallion has raised script that reads "Back Staff". The bottom of the medallion image has a copyright symbol and "ACP". The reverse continues the excellent 3-D work. The madilion shows a robed man using a cross staff pointed at the sun for navigaion.  It goes as far as showing a far off ship on the water. The raised script in the medallion reads "Cross Staff".  Excellent show coin.

Info on the coin: From mid-August 2008, CoinsAndPins released this special geocoin as part of a whole "Navigation Geocoin" series in a total edition of 1390 pieces and three editions Antique Silver, Antique Bronze and one LE Black Nickel. The 50 x 5 mm large and therefore quite heavy Geocoin shows detailed 3-D high-relief images of the use of navigation instruments for precise positioning on both sides.

As a very early navigation instrument, the cross staff, also known as Jacob's staff, was widely used by surveyors and astronomers. The name is derived from its cross shape. It was cumbersome to use because a user had to focus on the horizon and the star or sun at the same time.

John Davis invented a rear rod in 1595 and its improved design became known as the Davis Quadrant. Aptly named, its basic design is like a cross staff, but with some improvements. Daylight measurements were taken with their backs to the sun. In many cases, John Davis' invention replaced not only the cross staff, but also the astrolabe and the sailor's quadrant. The back staff was in use until the end of the 18th century, when the octant and the sextant became the new preferred navigation instruments.

Navigation: The Cross Staff and the Back Staff: The cross-staff consisted of a long staff with a perpendicular vane which slides back and forth upon it. The staff is marked with graduated measurements, calculated by trigonometry. The angles can then be measured by holding it so the ends of the vane are level with the points to be measured. Early in the sixteenth century it was already in use as a seaman's navigational instrument. Originally the staff had only one vane and was very long. Therefore, it was very difficult to manage on a rocking ship. The mariners added more vanes in order to reduce the length of the staff to about 2 1/2 feet. The long, medium and short vanes on the staff were about 15, 10 and 6 inches in length. The staff was then calibrated directly into degrees for use on board a ship. For the most part, the cross-staff was used to find the latitude by measuring the altitude of the Pole Star above the horizon. This, of course, was useless in cloudy weather. It could also be used to determine the altitude of the sun, but this required the observer to look directly into the blinding sun. In the early seventeenth century, the back-staff was developed to avoid this problem. It would not be practical to make a cross-staff because of its length and detail. However, the teacher might want to include the worksheet as a coloring page to be added to the pupils' notebooks. Early in the sixteenth century it was already in use as a seaman's navigational instrument. It was introduced into England in the mid-sixteenth century, where it was further developed to measure the angles between stars, and to measure the heights of buildings or topographical features such as mountains and hills. A very early navigational instrument, the cross staff was widely used among surveyors and astronomers. It was not until the 1500s after it was developed further that it started to be used at sea. It was with the invention of the back staff that these problems would be resolved. John Davis invented a back staff in 1595 and his improved design became known as the Davis Quadrant. It rendered the cross staff obsolete since the user only had to take a sight at one object and didn't have to look at the sun to take a reading. Appropriately named, its basic design is like a cross staff, but with some enhancements. Daylight readings were taken by having your back towards the sun. In many cases, John Davis's invention ended up replacing not only the cross staff, but also the mariner's astrolabe and quadrant. It was in the late 1700s when the octant and sextant became the new preferred tools over the back staff.

Go to www.compassrosegeocoin.com/crossbackstaff.php for information on how it works.

So many of my trackables have been muggled that I release new GCs as virtuals. If you do not approve, please leave it in the cache for a cacher who understands. Thanks. BL