sundial
Definition
A sundial is a device that uses the sun's rays to tell the time of day. It is a simple and ancient instrument that has been used for centuries.
The basic principle of a sundial is that the sun's rays strike the Earth's surface at an angle that depends on the time of day. This angle can be used to determine the time by tracking the shadow of a gnomon, which is a vertical rod or pointer, cast on a calibrated surface.
Sundials can be made of a variety of materials, including stone, metal, and wood. They can be very simple or very complex, depending on their intended use.
Sundials are a popular decorative item, but they can also be used to teach about timekeeping and the solar system. They are also useful in places where there is no electricity or where clocks are not reliable.
How can the word be used?
The sundial was a gift from my grandfather.
Different forms of the word
Noun: sundial.
Etymology
The word "sundial" comes from the Old English words "sunne" (sun) and "dæl" (part). It was first used in English in the 14th century.
There are no other forms of the word "sundial".
The etymology of the word "sundial" is interesting because it shows how the word is related to its meaning. The word "sunne" literally means "sun", and "dæl" literally means "part", so a sundial is literally a "part of the sun".
Question
What is a sundial?
AQA Science Exam Question and Answer
Question:
Describe the science behind a sundial and how it functions as a timekeeping device. Explain the relationship between the Sun's position and the shadow cast by the sundial, and discuss its limitations in modern timekeeping.
Answer:
A sundial is a timekeeping device that relies on the position of the Sun to indicate the time of day. It consists of a flat plate with a rod called a gnomon protruding upward. As the Sun moves across the sky, the gnomon's shadow shifts, allowing observers to determine the time based on the shadow's position.
The relationship between the Sun's position and the shadow's direction is governed by Earth's rotation. When the Sun is directly overhead, the gnomon's shadow is shortest, indicating noon. As the Sun's angle changes, the shadow lengthens, corresponding to different times.
However, sundials have limitations. They are most accurate near the equator and vary in accuracy with location and season due to Earth's axial tilt and orbit. They are also impractical on cloudy or overcast days when the Sun's position is obscured.
In modern times, precise timekeeping relies on atomic clocks and digital devices. Nevertheless, sundials offer a simple and elegant way to understand the Earth-Sun relationship and the passage of time, reflecting the ingenious use of celestial mechanics by ancient civilizations to measure time before the advent of sophisticated timekeeping technologies.