In atmospheric and environmental physics, the instrument specifically designed to measure the degree of blueness of the sky or the ocean is known by which name?

Introduction / Context:
Many specialised instruments exist in physics, meteorology, and environmental science to measure different properties of the atmosphere and oceans. While common devices like thermometers and barometers are widely known, more specialised instruments are sometimes asked in general knowledge and competitive exams. This question focuses on the name of the instrument used to measure the blueness of the sky or the sea, which is related to how light scatters in the atmosphere or water.

Given Data / Assumptions:

• The instrument is used to measure the degree of blueness.
• The blueness can refer to the sky or the surface appearance of the ocean.
• The options list several different scientific instruments.

Concept / Approach:
The word root “cyano” comes from a Greek term meaning blue. A cyanometer is an instrument with a graded scale of blue colour samples that allows observers to compare and quantify how blue the sky appears. It was historically used to study atmospheric conditions, dust content, and humidity that influence sky colour. Other instruments in the options measure different physical properties, not colour or blueness, so recognising the meaning of the prefixes and common uses of these devices helps to identify the correct answer.

Step-by-Step Solution:
Step 1: Look for clues in the names of the instruments, such as prefixes that suggest their function. Step 2: Note that “cyano” is associated with the colour blue, suggesting a link to blueness. Step 3: Recall that a cyanometer is historically used to measure and compare sky blue intensity. Step 4: Confirm that other instruments listed are used for different purposes, and select cyanometer as the correct option.

Verification / Alternative check:
A quick context check for the other instruments helps verify the choice. A barometer measures atmospheric pressure, which is important for weather prediction but not directly for colour measurement. A bathymeter is associated with measuring depth, particularly in oceans. A ceraunograph is related to recording thunder or lightning. Only cyanometer fits the description of measuring blueness, confirming our selection.

Why Other Options Are Wrong:

• Bathymeter: This instrument is used to measure water depth, especially in oceans, and has no direct connection to measuring colour.
• Ceraunograph: This device is used to record lightning or thunder activity and is associated with storms, not sky colour.
• Barometer: This measures atmospheric pressure and is widely used in meteorology but does not quantify blueness of the sky or ocean.

Common Pitfalls:
Many learners are unfamiliar with rare instruments and may guess based on what they have heard most often, such as barometer. Another confusion arises from not recognising common prefixes like “cyano”. Developing the habit of breaking scientific terms into their roots can help deduce meanings even for unfamiliar words. For example, remembering that “baro” relates to pressure, “bathys” to depth, and “cyano” to blue gives a powerful tool for educated guessing.

Final Answer:
The instrument for measuring the blueness of the sky or ocean is called a cyanometer.