astronomy

NGC 251

NGC 251 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 251 rather than just read about it. In short: NGC 251 is a spiral galaxy in the constellation of Pisces. Its velocity with respect to the cosmic microwave background for is 4,224±23 km/s, which corresponds to a Hubble distance of 203.2 ± 14.3 Mly (62.30 ± 4.37 Mpc).

Key takeaways

NGC 251 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 251 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 251 from memory before moving on to harder problems.

Reference excerpt

NGC 251 is a spiral galaxy in the constellation of Pisces. Its velocity with respect to the cosmic microwave background for is 4,224±23 km/s, which corresponds to a Hubble distance of 203.2 ± 14.3 Mly (62.30 ± 4.37 Mpc). Additionally, six non redshift measurements give a distance of 205.32 ± 5.54 Mly (62.950 ± 1.699 Mpc). It was discovered on October 15, 1784, by German-British astronomer William Herschel. According to I.D. Karachentsev, NGC 251 forms an isolated galaxy pair with UGC 477. One supernova has been observed in NGC 251: SN 2023rky (Type II, mag. 18.6) was discovered by the Zwicky Transient Facility on 6 September 2023.

Notes

Illustrations

Worked examples

Example 1 — a first encounter with NGC 251

Start with the simplest possible case. Write down what NGC 251 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 251 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 251 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 251

In research: NGC 251 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 251 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 251 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1784, Discoveries by William Herschel, MCG objects, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 251 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “NGC 251” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study NGC 251 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 251 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 251 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 251 in simple terms?

Why does NGC 251 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 251?

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 251.