astronomy

NGC 684

NGC 684 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 684 rather than just read about it. In short: NGC 684 is a spiral galaxy approximately 135 million light-years away from Earth in the constellation of Triangulum. It was discovered by William Herschel on October 26, 1786.

Key takeaways

NGC 684 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 684 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 684 from memory before moving on to harder problems.

Reference excerpt

NGC 684 is a spiral galaxy approximately 135 million light-years away from Earth in the constellation of Triangulum. It was discovered by William Herschel on October 26, 1786. Edward Swift, Lewis's son, found this galaxy again on 18 Jan 1890 while "searching for Swift's Comet." and it was reported as a new object in list IX-6.

NGC 684 Group NGC 684 is the largest member of a group of galaxies named after it (also known as LGG 32), which includes the galaxies NGC 670 and IC 1731.

Supernovae Two supernovae have been observed in NGC 684:

SN 2021ass (Type II, mag. 18.1122) was discovered by the Zwicky Transient Facility on 18 January 2021. SN 2025aml (Type II, mag. 18.1168) was discovered by the Zwicky Transient Facility on 31 January 2025.

See also Spiral galaxy List of NGC objects (1–1000) Triangulum (constellation)

References

External links Media related to NGC 684 at Wikimedia Commons

NGC 684 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images SEDS

Illustrations

Worked examples

Example 1 — a first encounter with NGC 684

Start with the simplest possible case. Write down what NGC 684 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 684 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 684 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 684

In research: NGC 684 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 684 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 684 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1786, Discoveries by William Herschel, IC objects, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 684 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 684 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 684 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 684 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 684 in simple terms?

NGC 684 is a spiral galaxy approximately 135 million light-years away from Earth in the constellation of Triangulum. It was discovered by William Herschel on October 26, 1786.

Why does NGC 684 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 684?

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 684.