astronomy

NGC 681

NGC 681 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 NGC 681 rather than just read about it. In short: NGC 681 is an intermediate spiral galaxy in the constellation of Cetus, located approximately 66.5 million light-years from Earth. NGC 681 is a member of the MCG -02-05-053 group (also known as LGG 33), which contains four galaxies, including NGC 701 and IC 1738.

Key takeaways

NGC 681 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect NGC 681 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 681 from memory before moving on to harder problems.

Reference excerpt

NGC 681 is an intermediate spiral galaxy in the constellation of Cetus, located approximately 66.5 million light-years from Earth. NGC 681 is a member of the MCG -02-05-053 group (also known as LGG 33), which contains four galaxies, including NGC 701 and IC 1738.

Observation history NGC 681 was discovered by the German-born British astronomer William Herschel on 28 November 1785 and was later also observed by William's son, John Herschel. John Louis Emil Dreyer, compiler of the first New General Catalogue of Nebulae and Clusters of Stars, described NGC 681 as being a "pretty faint, considerably large, round, small (faint) star 90 arcsec to [the] west" that becomes "gradually a little brighter [in the] middle".

Physical characteristics NGC 681 shares many structural similarities with the Sombrero Galaxy, M104, although it is smaller, less luminous, and less massive. Its thin, dusty disc is seen almost perfectly edge-on and features a small, very bright nucleus in the center of a very pronounced bulge. Distinctly unlike M104, NGC 681's disc contains many H II regions, where star formation is likely to be occurring. The galaxy has a mass of 1.9×1010 M☉, a mass-to-light ratio of 3.6 Υ ⊙ {\displaystyle \Upsilon \odot } , and a spiral pattern which is asymmetrical. The SIMBAD database lists NGC 681 as a Seyfert II Galaxy, i.e. it has a quasar-like nucleus with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, the host galaxy is clearly detectable.

Supernova One supernova has been observed in NGC 681.

SN 2024abup (Type Ic-BL, mag. 17.018) was discovered by ATLAS on 22 November 2024.

Image gallery

See also List of NGC objects (1–1000) Sombrero Galaxy Messier object List of spiral galaxies

References

External links Media related to NGC 681 at Wikimedia Commons

Illustrations

Worked examples

Example 1 — a first encounter with NGC 681

Start with the simplest possible case. Write down what NGC 681 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 NGC 681 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 NGC 681 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 NGC 681

In research: NGC 681 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 NGC 681 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: NGC 681 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cetus (constellation), Discoveries by William Herschel, Galaxies discovered in 1785, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 681 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 NGC 681 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 681 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 NGC 681 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 681 in simple terms?

Why does NGC 681 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 NGC 681?

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 NGC 681.