astronomy

NGC 2721

NGC 2721 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 2721 rather than just read about it. In short: NGC 2721 is a barred spiral galaxy in the constellation of Hydra. Its velocity with respect to the cosmic microwave background is 4,028±22 km/s, which corresponds to a Hubble distance of 193.8 ± 13.6 Mly (59.41 ± 4.17 Mpc).

Key takeaways

NGC 2721 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 2721 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 2721 from memory before moving on to harder problems.

Reference excerpt

NGC 2721 is a barred spiral galaxy in the constellation of Hydra. Its velocity with respect to the cosmic microwave background is 4,028±22 km/s, which corresponds to a Hubble distance of 193.8 ± 13.6 Mly (59.41 ± 4.17 Mpc). Additionally, 13 non-redshift measurements give a similar mean distance of 190.90 ± 7.29 Mly (58.531 ± 2.235 Mpc). It was discovered by German-British astronomer William Herschel on 1 February 1786. NGC 2721 is 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 2721:

SN 2024xjl (Type Ib/c, mag. 17.605) was discovered by ATLAS on 5 October 2024.

See also List of NGC objects (2001–3000)

References

External links Media related to NGC 2721 at Wikimedia Commons NGC 2721 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

Illustrations

Worked examples

Example 1 — a first encounter with NGC 2721

Start with the simplest possible case. Write down what NGC 2721 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 2721 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 2721 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 2721

In research: NGC 2721 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 2721 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 2721 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1786, Barred spiral galaxies, Discoveries by William Herschel, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 2721 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 2721” →

Affiliate

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

How to study NGC 2721 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 2721 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 2721 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 2721 in simple terms?

Why does NGC 2721 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 2721?

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 2721.