astronomy

Solar cycle 21

Solar cycle 21 is a astronomy 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 Solar cycle 21 rather than just read about it. In short: Solar cycle 21 was the 21st solar cycle since 1755, when extensive recording of solar sunspot activity began. The solar cycle lasted 10.5 years, beginning in March 1976 and ending in September 1986.

Key takeaways

Solar cycle 21 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Solar cycle 21 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Solar cycle 21 from memory before moving on to harder problems.

Reference excerpt

Solar cycle 21 was the 21st solar cycle since 1755, when extensive recording of solar sunspot activity began. The solar cycle lasted 10.5 years, beginning in March 1976 and ending in September 1986. The maximum smoothed sunspot number observed during the solar cycle was 232.9, in December 1979, and the starting minimum was 17.8. During the minimum transit from solar cycle 21 to 22, there were a total of 273 days with no sunspots. The largest solar flare of this cycle (X15) occurred on July 11, 1978. This solar cycle marked the beginning of systematic monitoring of the total solar irradiance from space.

See also Solar variation List of solar cycles

References

Illustrations

Worked examples

Example 1 — a first encounter with Solar cycle 21

Start with the simplest possible case. Write down what Solar cycle 21 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, 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 Solar cycle 21 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 Solar cycle 21 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 Solar cycle 21

In research: Solar cycle 21 appears in astronomy 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 Solar cycle 21 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: Solar cycle 21 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Solar cycles, Sun stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Solar cycle 21 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Solar cycle 21 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Solar cycle 21 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 Solar cycle 21 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Solar cycle 21 in simple terms?

Solar cycle 21 was the 21st solar cycle since 1755, when extensive recording of solar sunspot activity began. The solar cycle lasted 10.5 years, beginning in March 1976 and ending in September 1986.

Why does Solar cycle 21 matter?

Because it connects several astronomy 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 Solar cycle 21?

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 Solar cycle 21.