earth science

Sunshine duration

Sunshine duration is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sunshine duration rather than just read about it. In short: Sunshine duration or sunshine hours is a climatological indicator, measuring duration of sunshine in given period (usually, a day or a year) for a given location on Earth, typically expressed as an averaged value over several years. It is a general indicator of cloudiness of a location, and thus differs from insolation, which measures the total energy delivered by sunlight over a given period.

Key takeaways

Sunshine duration belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sunshine duration to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sunshine duration from memory before moving on to harder problems.

Reference excerpt

Sunshine duration or sunshine hours is a climatological indicator, measuring duration of sunshine in given period (usually, a day or a year) for a given location on Earth, typically expressed as an averaged value over several years. It is a general indicator of cloudiness of a location, and thus differs from insolation, which measures the total energy delivered by sunlight over a given period. Sunshine duration is usually expressed in hours per year, or in (average) hours per day. The first measure indicates the general sunniness of a location compared with other places, while the latter allows for comparison of sunshine in various seasons in the same location. Another often-used measure is percentage ratio of recorded bright sunshine duration to daylight duration in the observed period. An important use of sunshine duration data is to characterize the climate of sites, especially of health resorts. This also takes into account the psychological effect of strong solar light on human well-being. It is often used to promote tourist destinations.

Daytime duration

If the Sun were to be above the horizon 50% of the time for a standard year consisting of 8,760 hours, apparent maximal daytime duration would be 4,380 hours for any point on Earth. However, there are physical and astronomical effects that change that picture. Namely, atmospheric refraction allows the Sun to be still visible even when it physically sets below the horizon. For that reason, average daytime (disregarding cloud effects) is longest in polar areas, where the apparent Sun spends the most time around the horizon. Places on the Arctic Circle have the longest total annual daytime, 4,647 hours, while the North Pole receives 4,575. Because of elliptic nature of the Earth's orbit, the Southern Hemisphere is not symmetrical: the Antarctic Circle, with 4,530 hours of daylight, receives five days less of sunshine than its antipodes. The Equator has a total daytime of 4,422 hours per year.

Definition and measurement Given the theoretical maximum of daytime duration for a given location, there is also a practical consideration at which point the amount of daylight is sufficient to be treated as a "sunshine hour". "Bright" sunshine hours represent the total hours when the sunlight is stronger than a specified threshold, as opposed to just "visible" hours. "Visible" sunshine, for example, occurs around sunrise and sunset, but is not strong enough to excite a standardized sensor. Measurement is performed by instruments called sunshine recorders. For the specific purpose of sunshine duration recording, Campbell–Stokes recorders are used, which use a spherical glass lens to focus the sun rays on a specially designed tape. When the intensity exceeds a predetermined threshold, the tape burns. The total length of the burn trace is proportional to the number of bright hours. Another type of recorder is the Jordan sunshine recorder. Newer, electronic recorders have more stable sensitivity than that of the paper tape. In order to harmonize the data measured worldwide, in 1962 the World Meteorological Organization (WMO) defined a standardized design of the Campbell–Stokes recorder, called an Interim Reference Sunshine Recorder (IRSR). In 2003, the sunshine duration was finally defined as the period during which direct solar irradiance exceeds a threshold value of 120 W/m2.

Geographic distribution

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Sunshine duration

Start with the simplest possible case. Write down what Sunshine duration claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sunshine duration before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sunshine duration ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sunshine duration

In research: Sunshine duration appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sunshine duration in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sunshine duration is common in secondary-school and first-year university syllabi. It links to neighbouring topics Atmospheric radiation, Climate and weather statistics, so understanding it makes those chapters shorter.
In everyday life: Look for Sunshine duration outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sunshine duration in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sunshine duration means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sunshine duration out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sunshine duration in simple terms?

Why does Sunshine duration matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sunshine duration?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sunshine duration.