astronomy

NGC 747

NGC 747 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 747 rather than just read about it. In short: NGC 747 is a spiral galaxy located in the constellation Cetus. Its speed relative to the cosmic microwave background is 5,100 ± 19 km/s, which corresponds to a Hubble distance of 75.2 ± 5.3 Mpc (~245 million ly).

Key takeaways

NGC 747 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 747 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 747 from memory before moving on to harder problems.

Reference excerpt

NGC 747 is a spiral galaxy located in the constellation Cetus. Its speed relative to the cosmic microwave background is 5,100 ± 19 km/s, which corresponds to a Hubble distance of 75.2 ± 5.3 Mpc (~245 million ly). NGC 747 was discovered by American astronomer Francis Leavenworth in 1886. The luminosity class of NGC 747 is II and it has a broad HI line. To date, four non-redshift measurements yield a distance of 83.900 ± 4.166 Mpc (~274 million ly), which is within the Hubble distance range. Note, however, that it is with the average value of independent measurements, when they exist, that the NASA/IPAC database calculates the diameter of a galaxy and that consequently the diameter of NGC 747 could be approximately 23 .9 kpc (~78,000 ly). In the same area of the sky there are, among other things: the galaxies NGC 713, NGC 731, NGC 755 and NGC 767.

See also List of NGC objects (1–1000) Lists of galaxies Galaxy cluster

References

External links NGC 747 at SEDS USA NGC 747 at SIMBAD

Illustrations

Worked examples

Example 1 — a first encounter with NGC 747

Start with the simplest possible case. Write down what NGC 747 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 747 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 747 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 747

In research: NGC 747 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 747 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 747 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1886, Cetus (constellation), Discoveries by Francis Leavenworth, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 747 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 747 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 747 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 747 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 747 in simple terms?

Why does NGC 747 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 747?

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 747.