SEXTANT Flashcards
What are adjustable errors
Perpendicularity
Side Error
Index Error
Picture of sextant, name the parts
What is sextant used for
A sextant is a navigational instrument used primarily for celestial navigation at sea. It is designed to measure the angle between two objects, typically the horizon and a celestial body such as the sun, moon, or stars
How would you use a sextant
Set Up: Ensure that the sextant is properly adjusted and calibrated.
Check that the mirrors are clean and aligned correctly. Set the sextant’s index arm or micrometer drum to zero.
Choose a Celestial Body: Select a celestial body to observe, such as the sun, moon, or a bright star. Consider factors like visibility, time of day, and the body’s position relative to the horizon.
Align with the Horizon: Hold the sextant steady and look through the horizon mirror or index mirror. Adjust the sextant’s frame or handle until the horizon appears aligned with the celestial body’s image reflected in the mirror.
Sight the Celestial Body: Use the sextant’s index arm or micrometer drum to bring the image of the celestial body into view through the index mirror. This may require fine adjustments to ensure the body is accurately sighted.
Read the Angle: Once the celestial body is aligned with the horizon, read the angle indicated on the sextant’s scale. This angle represents the altitude of the celestial body above the horizon.
Record Time: Record the time of the observation using an accurate timekeeping device, such as a chronometer or GPS receiver. The time is essential for calculating the celestial body’s position accurately.
Calculate Position: Use sight reduction tables, such as those found in nautical almanacs, to calculate the ship’s position based on the observed altitude of the celestial body, the time of observation, and other relevant factors.
Repeat Observations: Take multiple observations of celestial bodies over time to obtain a more accurate position fix and to account for factors such as the ship’s movement and changes in celestial body positions.
Apply Corrections: Apply corrections for factors such as atmospheric refraction, index error, and vessel motion to refine the calculated position fix.
Plot Position: Plot the calculated position fix on a nautical chart using latitude and longitude coordinates to determine the ship’s exact location.
How do you adjust errors
What do you do if reading is off the arc
What are fixed errors
Shown two slides of readings to take (some are on and off the arc)
Tell me about sextant
What is a sextant
Explain side errors & correction
Where would the arm be for a side error correction
What piece of sextant would you use to correct this
What is the name of the fixed error of the telescope
How do you use a sextant for position fixes and compass correction
