astronomy

NGC 2139

NGC 2139 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 2139 rather than just read about it. In short: NGC 2139 is a barred spiral galaxy in the constellation of Lepus. It was discovered on November 17, 1784, by the German-English astronomer William Herschel.

Key takeaways

NGC 2139 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 2139 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 2139 from memory before moving on to harder problems.

Reference excerpt

NGC 2139 is a barred spiral galaxy in the constellation of Lepus. It was discovered on November 17, 1784, by the German-English astronomer William Herschel. The galaxy is located at a distance of 120.6 million light-years (36.98 Mpc) from the Sun and is receding with a radial velocity of 1,836 km/s. The overall form of this galaxy is irregular with spiral arms and the appearance of tidal features, suggesting a potential recent merger event. There is no central bulge of significance. The morphological classification is SAB(rs)cd, which indicates a barred spiral galaxy (SAB) with a transitional inner ring structure (rs) and loosely wound spiral arms (cd). It is a star forming galaxy with a formation rate of 3.8 M☉·yr−1. There is a plume extending to the south of the galaxy. A luminous filament runs through the center of the galaxy, which includes a small nuclear cluster. This cluster is only 4.1×107 years old with a mass of 8.3×105 M☉. It is offset at a distance of 320 pc from the center of the galaxy and may come to rest there on a time scale of around 100 million years. The cluster is a source of X-ray emission.

Supernovae Three supernovae have been observed in NGC 2139:

Robert Evans and associates discovered SN 1995ad (Type II, mag. 14) on 28 September 1995. It was positioned in one of the spiral arms, 25″ west and 5″ south of the NGC 2139 nucleus. The recession velocity was consistent with that of the host galaxy. SN 2022qhy (Type Ibn, mag. 15.889) was discovered by ATLAS on 1 August 2022. SN 2023zcu (Type II, mag. 19.054) was discovered by ATLAS on 8 December 2023.

References

Illustrations

Worked examples

Example 1 — a first encounter with NGC 2139

Start with the simplest possible case. Write down what NGC 2139 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 2139 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 2139 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 2139

In research: NGC 2139 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 2139 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 2139 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1784, Barred spiral galaxies, Discoveries by William Herschel, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 2139 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 2139 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 2139 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 2139 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 2139 in simple terms?

NGC 2139 is a barred spiral galaxy in the constellation of Lepus. It was discovered on November 17, 1784, by the German-English astronomer William Herschel.

Why does NGC 2139 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 2139?

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 2139.