astronomy

John Louis Emil Dreyer

John Louis Emil Dreyer 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 John Louis Emil Dreyer rather than just read about it. In short: John Louis Emil Dreyer (13 February 1852 – 14 September 1926), also Johan Ludvig Emil Dreyer, was a Danish astronomer who spent most of his career working in Ireland. He spent the last decade of his life in Oxford, England.

Key takeaways

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

Reference excerpt

John Louis Emil Dreyer (13 February 1852 – 14 September 1926), also Johan Ludvig Emil Dreyer, was a Danish astronomer who spent most of his career working in Ireland. He spent the last decade of his life in Oxford, England.

Life Dreyer was born in Copenhagen. His father, Lieutenant General John Christopher Dreyer, was the Danish Minister for War and the Navy. When he was 14 he became interested in astronomy and regularly visited Hans Schjellerup at the Copenhagen observatory. He was educated in Copenhagen, taking an MA in 1872. While the same university later awarded him a PhD, in 1874. But in 1874, at the age of 22, he went to Parsonstown, Ireland. There he worked as the assistant of Lord Rosse (the son and successor of the Lord Rosse who built the Leviathan of Parsonstown telescope). During 1878 he moved to Dunsink, the site of the Trinity College Observatory of Dublin University to work for Robert Stawell Ball. In 1882 he relocated again, this time to Armagh Observatory, where he served as Director until his retirement in 1916. In 1885 he became a British citizen. In 1916 he and his wife Kate moved to Oxford where Dreyer worked on editing the works of Tycho Brahe. He won the Gold Medal of the Royal Astronomical Society in 1916 and served as the society's president from 1923 until 1925. He died on 14 September 1926 in Oxford, where he is buried in Wolvercote Cemetery. A crater on the far side of the Moon is named after him.

Works Dreyer compiled the New General Catalogue of Nebulae and Clusters of Stars, basing it on William Herschel's Catalogue of Nebulae, as well as two supplementary Index Catalogues. The NGC and IC catalogue designations are still widely used. Dreyer was also a historian of astronomy. In 1890 he published a biography of Danish astronomer Tycho Brahe, and in his later years he edited Tycho's publications and unpublished correspondence. These were published in a 15-volume edition, Opera Omnia, the last volume of which was published after his death. His book History of the Planetary Systems from Thales to Kepler (1905), is currently printed with the title A History of Astronomy from Thales to Kepler. He co-edited the first official history of the Royal Astronomical Society along with Herbert Hall Turner, History of the Royal Astronomical Society 1820–1920 (1923, reprinted 1987).

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References

External links

Biography with picture

Illustrations

Worked examples

Example 1 — a first encounter with John Louis Emil Dreyer

Start with the simplest possible case. Write down what John Louis Emil Dreyer 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 John Louis Emil Dreyer 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 John Louis Emil Dreyer 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 John Louis Emil Dreyer

In research: John Louis Emil Dreyer 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 John Louis Emil Dreyer 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: John Louis Emil Dreyer is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1852 births, 1926 deaths, 19th-century British astronomers, so understanding it makes those chapters shorter.
In everyday life: Look for John Louis Emil Dreyer 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 John Louis Emil Dreyer in 20 minutes

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

Frequently asked questions

What is John Louis Emil Dreyer in simple terms?

Why does John Louis Emil Dreyer 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 John Louis Emil Dreyer?

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 John Louis Emil Dreyer.