The backstaff is a navigational instrument that was used to measure the altitude of a celestial body, in particular the Sun or Moon. When observing the Sun, users kept the Sun to their back (hence the name) and observed the shadow cast by the upper vane on a horizon vane.
What was a cross-staff and back staff?
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. The name is derived from its cross shape.
What is the back staff made of?
The backstaff is made from a lignum vitae frame with boxwood arcs and crossbar, and brass rivets. There is an inlaid boxwood plate on the main strut. The staff also has a boxwood horizon vane and shadow vane.
How do you use a cross-staff?
To use the cross-staff, start by sliding the cross-piece to about the middle of the yardstick. Sight the yardstick along the line halfway between the stars whose separation you want to measure, then place the two sliders on the cross-piece so that the slits are approximately where the stars are located.
Is the cross-staff still used?
The cross-staff was used into the 17th and 18th centuries. By 1750, the octant was the preferred tool for measuring altitude. Therefore, the cross-staff became less popular, and use of this tool eventually diminished.
What replaced the cross-staff?
A navigational instrument for measuring the altitude of the sun, introduced in the 16th century. It got its name because, unlike the cross-staff that it replaced, the user has the sun behind him when using the instrument.
What is a cross-staff on a boat?
: an instrument formerly used at sea for taking the altitude of a celestial body.
What do you use a sextant for?
Sextant, instrument for determining the angle between the horizon and a celestial body such as the Sun, the Moon, or a star, used in celestial navigation to determine latitude and longitude. The device consists of an arc of a circle, marked off in degrees, and a movable radial arm pivoted at the centre of the circle.
What is a Davis quadrant?
In the 17th and 18th centuries the principal instrument of the navigator at sea was the Davis quadrant, also known as English quadrant, a forerunner of the sextant. It was used to measure the altitude of the sun at noon, replacing the ancient and less accurate astrolabe in the determination of latitude.
How do you use quadrants in navigation?
Continuing to hold the plumb line between your thumb and forefinger, tilt the quadrant over and read the angle where the line crosses the scale at the edge of the quadrant radius. This is your latitude.
What is a quadrant in history?
of American History. Quadrants were used to measure altitudes of celestial objects and were especially useful for mapping the sky. They consisted of a sighting device mounted on a quarter circle, or quadrant, which was engraved with degree markings.
What is the synonym of backstop?
Phrases Synonymous with backstopping. bearing a hand, standing one in good stead.
When was the Davis quadrant invented?
The Davis Quadrant was the successor of the cross-staff and the predecessor of the octant. The instrument was based on a backstaff invented by Captain John Davis which he first described in his Seamen’s Secrets published in 1595.
What is the use of a cross-staff?
The cross-staff is an instrument used to measure angles and altitudes, consisting of a trigonometrically graduated staff and one or more perpendicular vanes moving over it.
Who invented Jacobs staff?
The original Jacob’s staff, or cross-staff, was a single pole device credited to Levi ben Gerson (1288-1344), who was one of the leading Jewish mathematicians of the 14th century.
How do you make a Jacob’s staff?
- Decide what length you would like the staff to be: 1.0 m or 1.5 m. …
- Cut the pipe to be 1 cm LESS than your desired length. …
- Place the PVC end caps on either end of the pipe. …
- Use the marker and tape measure to mark the pipe at 10 cm increments. …
- At alternate intervals on the staff, wrap electrical tape between the notches.
What is the height of cross-staff?
use in navigation. …than its 16th-century successor, the cross-staff, a simple device consisting of a staff about 3 feet (1 metre) long fitted with a sliding crosspiece (see photograph).
How was the cross-staff used with stars?
Astronomers used the cross-staff for measuring the angle between the directions of two stars. … Ships’ officers used it to measure the elevation angle of the noontime Sun above the horizon, which allowed them to estimate their latitude (see section on navigation).
What is Open cross-staff?
The Open cross-staff consists of a long staff with a perpendicular vane which slides to and fro upon it. These open frame tripods are comes with lemon yellow powder coated and silver anodized. Features: Used to measure the altitude of the sun. Used as a navigation instrument.
How do you read a Cross staff?
The staff reading is the reading on the staff at which the horizontal hair appears to cut the staff. A staff reading consists of 4 digits. The first digit represents the whole number of meters, the second digit represents decimeters, and the third, and fourth digits represent millimeters.
How many types of Cross staff are there?
10. How many types of cross staff are available? Explanation: The three types are open cross staff, French cross staff and adjustable cross staff. Open cross staff has two vertical, opposite slits.
What is adjustable Cross staff?
ADJUSTABLE CROSS STAFF: It consists of two cylinders of equal diameter placed one over each another and is used to set of any angle.