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astronomy

Solar cycle 20

Solar cycle 20 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 20 rather than just read about it. In short: Solar cycle 20 was the twentieth solar cycle since 1755, when extensive recording of solar sunspot activity began. The solar cycle lasted 11.4 years, beginning in October 1964 and ending in March 1976.

Solar cycle 20 — main illustration
Solar cycle 20 — illustration

Key takeaways

  • Solar cycle 20 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 20 to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Solar cycle 20 from memory before moving on to harder problems.

Reference excerpt

Solar cycle 20 was the twentieth solar cycle since 1755, when extensive recording of solar sunspot activity began. The solar cycle lasted 11.4 years, beginning in October 1964 and ending in March 1976. The maximum smoothed sunspot number observed during the solar cycle was 156.6 (November 1968), and the starting minimum was 14.3. During the minimum transit from solar cycle 20 to 21, there were a total of 272 days with no sunspots. Comparison with other cycles shows that geomagnetic activity during the declining phase of cycle 20 (1973–1975) was unusually high. Heavy solar activity was a factor in causing the earlier-than-expected atmospheric reentry of Skylab in 1979. Data from solar cycle 20 was used to build the K-1974 solar proton fluence model, used for planning space missions during solar cycle 21.

August 1972 solar storm

An extremely active active region, McMath 11976, produced a historic series of solar flares and coronal mass ejections (CMEs) in August 1972. One CME traveled to Earth in a record low of 14.6 hours and produced a strong geomagnetic storm that caused widespread electrical and communications grid disturbances and the accidental detonation of numerous U.S. Navy magnetic sea mines in North Vietnam.

See also List of solar cycles

References

Illustrations

Solar cycle 20 illustration
Solar cycle 20: One of the largest solar prominences ever recorded, from solar cycle 20 (19 December 1973).[1]
One of the largest solar prominences ever recorded, from solar cycle 20 (19 December 1973).[1]

Worked examples

Example 1 — a first encounter with Solar cycle 20

Start with the simplest possible case. Write down what Solar cycle 20 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 20 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 20 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 20

In research
Solar cycle 20 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 20 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 20 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 20 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 Solar cycle 20 in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Solar cycle 20 means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Solar cycle 20 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Solar cycle 20 in simple terms?

Solar cycle 20 was the twentieth solar cycle since 1755, when extensive recording of solar sunspot activity began. The solar cycle lasted 11.4 years, beginning in October 1964 and ending in March 1976.

Why does Solar cycle 20 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 20?

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 20.

Tags

  • Solar cycles
  • Sun stubs

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