Precision Sighting: Measuring Angles with a Sextant

6th Grade

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| By Thames

Thames

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| Attempts: 12 | Questions: 20 | Updated: Feb 25, 2026

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1. What is the primary purpose of a sextant in navigation?

To measure the depth of the ocean

To measure the angle between two objects, like a star and the horizon

To tell the temperature of the water

To speed up a sailing ship

To measure the weight of the cargo

If a sailor needs to find their location at sea, and if they can measure the height of the Sun above the water line, then they can use that angle to calculate their position.

Explanation

If a sailor needs to find their location at sea, and if they can measure the height of the Sun above the water line, then they can use that angle to calculate their position.

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About This Quiz

Precision Sighting: Measuring Angles With A Sextant - Quiz

You do not need a full 360 degree circle to master the horizon when you have the mathematical elegance of a sextant in your hands. This iconic tool uses a sixty degree arc to unlock the secrets of navigation and measuring angles with a sextant is the definitive skill of... see moreevery legendary explorer. By bringing the sun down to the horizon line, you turn a simple curve of brass into a powerful data point. Discover how a fraction of a circle provides all the leverage you need to map the entire world.
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2. Why is the tool named "sextant"?

It has six different mirrors

Its frame is an arc that is 1/6th of a full circle

It was invented by six different people

It only works for six hours a day

It can see six planets at once

If a full circle is 360 degrees, and if 360 is divided by 6, the result is 60 degrees. If the physical frame of the tool covers a 60-degree arc, then it is called a sextant.

Explanation

If a full circle is 360 degrees, and if 360 is divided by 6, the result is 60 degrees. If the physical frame of the tool covers a 60-degree arc, then it is called a sextant.

Submit

3. When measuring angles with a sextant, the navigator usually looks at the horizon and a celestial body at the same time.

True

False

If the tool uses mirrors to bring the image of a star down to the level of the horizon, then the observer must see both items in the same viewfinder to line them up.

Explanation

If the tool uses mirrors to bring the image of a star down to the level of the horizon, then the observer must see both items in the same viewfinder to line them up.

Submit

4. When measuring angles with a sextant, the angle is measured in units called ________.

If the sky is shaped like a giant dome or circle, and if we use standard geometric units to measure parts of a circle, then the measurement is recorded in degrees.

Explanation

If the sky is shaped like a giant dome or circle, and if we use standard geometric units to measure parts of a circle, then the measurement is recorded in degrees.

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5. Even though the sextant's arc is only 60 degrees, it can measure angles up to 120 degrees. Why?

Because it uses a magnifying glass

Because of the principle of double reflection in mirrors

Because the user moves twice as fast

It is just a magic trick

Because the Sun is very large

If light bounces off two mirrors (the index mirror and the horizon glass), then the angle of the reflected light is doubled; if the physical arc is 60 degrees, then the double reflection allows for a measurement of 120 degrees.

Explanation

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6. Which of the following are main parts used when measuring angles with a sextant?

Index Arm

Telescope

Horizon Glass

Anemometer

Micrometer Drum

If a sextant requires a way to move the mirror (index arm), see the object (telescope), see the water line (horizon glass), and make tiny adjustments (micrometer drum), then these are all essential parts. An anemometer measures wind, not angles.

Explanation

Submit

7. What is the "Horizon Glass" on a sextant?

A mirror that is completely solid

A mirror that is half-silvered (half clear, half mirror)

A lens that changes the color of the sky

A piece of wood that holds the tool

A battery compartment

If the user needs to see the horizon (through clear glass) and the reflected star (in a mirror) at the same time, then the horizon glass must be half-clear and half-reflective.

Explanation

If the user needs to see the horizon (through clear glass) and the reflected star (in a mirror) at the same time, then the horizon glass must be half-clear and half-reflective.

Submit

8. A sextant needs a computer and batteries to function.

True

False

If a sextant is a mechanical tool that uses mirrors, scales, and human eyesight to find angles, then it is an analog instrument that works without any electricity.

Explanation

If a sextant is a mechanical tool that uses mirrors, scales, and human eyesight to find angles, then it is an analog instrument that works without any electricity.

Submit

9. The moving part of the sextant that allows the user to adjust the angle is called the index ________.

If the user must slide a metal bar along the arc to move the top mirror, and if that bar points to the degree marks on the scale, then that part is the index arm.

Explanation

If the user must slide a metal bar along the arc to move the top mirror, and if that bar points to the degree marks on the scale, then that part is the index arm.

Submit

10. What must a navigator use when measuring angles with a sextant to look at the Sun safely?

Sunglasses

A magnifying glass

Dark shade filters

A piece of paper

Their bare eyes

If looking directly at the Sun causes eye damage, and if a sextant is used to "bring the Sun down" to the horizon, then the tool must have dark colored glass filters to block the harmful brightness.

Explanation

If looking directly at the Sun causes eye damage, and if a sextant is used to "bring the Sun down" to the horizon, then the tool must have dark colored glass filters to block the harmful brightness.

Submit

11. Why is measuring angles with a sextant still taught to modern sailors?

GPS systems can fail or lose power

It is a reliable backup method

It helps them understand how the Earth moves

It makes the ship faster

It is a tradition in the Navy

If electronics break or satellites are blocked, a sailor needs a way to navigate. If the stars are always available and the tool is durable, it remains a vital skill for safety and understanding.

Explanation

If electronics break or satellites are blocked, a sailor needs a way to navigate. If the stars are always available and the tool is durable, it remains a vital skill for safety and understanding.

Submit

12. To get an accurate reading, what should the navigator do while holding the sextant?

Run across the deck

Swing or "rock" the sextant slightly

Close both eyes

Stand on one leg

Jump as high as possible

If the navigator wants to find the exact vertical height, they must find the lowest point of the arc the star makes. If they rock the tool, they can see the star just touch the horizon at its lowest point, ensuring the angle is correct.

Explanation

Submit

13. Measuring angles with a sextant allows you to find your "Altitude," which is how high an object is above the horizon.

True

False

If "altitude" in astronomy means the angular distance from the ground up to the star, and if that is exactly what the sextant measures, then the statement is true.

Explanation

If "altitude" in astronomy means the angular distance from the ground up to the star, and if that is exactly what the sextant measures, then the statement is true.

Submit

14. If you are measuring angles with a sextant at the North Pole, the star ________ would be almost exactly 90 degrees above you.

If the Earth has a North Pole axis, and if there is a star located directly above that axis, then that star is Polaris (the North Star).

Explanation

If the Earth has a North Pole axis, and if there is a star located directly above that axis, then that star is Polaris (the North Star).

Submit

15. What is the "Micrometer Drum" used for on a sextant?

To measure the weight of the tool

To make very small, precise measurements of minutes and seconds

To count how many stars are in the sky

To turn the telescope on and off

To change the height of the sailor

If a single degree is a large jump on the scale, and if a navigator needs to be accurate to within a mile, then they need a knob that allows for tiny adjustments smaller than one degree.

Explanation

If a single degree is a large jump on the scale, and if a navigator needs to be accurate to within a mile, then they need a knob that allows for tiny adjustments smaller than one degree.

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16. Which of the following can interfere with measuring angles with a sextant?

A cloudy night

Fog blocking the horizon

High waves making the ship unstable

The color of the boat's paint

Total darkness where the horizon is invisible

If the navigator cannot see the star (clouds) or the horizon (fog/darkness), or cannot hold the tool steady (waves), then they cannot take a reliable measurement.

Explanation

If the navigator cannot see the star (clouds) or the horizon (fog/darkness), or cannot hold the tool steady (waves), then they cannot take a reliable measurement.

Submit

17. If you measure the Sun at its highest point in the day (noon), what are you finding?

The distance to the Moon

The time of year

Your latitude (how far North or South you are)

The speed of the wind

The depth of the water

If the Sun's height at noon changes depending on how far North or South you travel, then measuring that peak angle allows you to calculate your latitude.

Explanation

If the Sun's height at noon changes depending on how far North or South you travel, then measuring that peak angle allows you to calculate your latitude.

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18. The frame of a sextant is usually made of metal like brass or aluminum to keep it from changing shape in different temperatures.

True

False

If the accuracy of the tool depends on the scale being perfect, and if wood or plastic might warp in the heat or cold, then a strong metal frame is necessary to maintain the exact 60-degree shape.

Explanation

If the accuracy of the tool depends on the scale being perfect, and if wood or plastic might warp in the heat or cold, then a strong metal frame is necessary to maintain the exact 60-degree shape.

Submit

19. One degree on a sextant is divided into 60 smaller parts called ________.

If a degree is too big for precise navigation, and if circles are traditionally divided into 60 parts for better detail, then those smaller units are called minutes of arc.

Explanation

If a degree is too big for precise navigation, and if circles are traditionally divided into 60 parts for better detail, then those smaller units are called minutes of arc.

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20. What is the final step in the process of measuring angles with a sextant?

Throwing the tool in the water

Reading the angle from the scale on the arc

Cleaning the mirrors with salt water

Drawing a picture of the star

Asking the captain for the answer

If the index arm has been moved and the star is perfectly aligned with the horizon, then the navigator must look at the numbers on the arc to see the final measurement they have captured.

Explanation

If the index arm has been moved and the star is perfectly aligned with the horizon, then the navigator must look at the numbers on the arc to see the final measurement they have captured.

Submit