astronomy

NGC 638

NGC 638 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 638 rather than just read about it. In short: NGC 638 is a barred spiral galaxy located in the constellation of Pisces. Its velocity speed to the cosmic microwave background is 2,864± 21 km/s, which corresponds to a Hubble's law of 42.2 ± 3.0 Mpc (~138 million light-year).

Key takeaways

NGC 638 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 638 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 638 from memory before moving on to harder problems.

Reference excerpt

NGC 638 is a barred spiral galaxy located in the constellation of Pisces. Its velocity speed to the cosmic microwave background is 2,864± 21 km/s, which corresponds to a Hubble's law of 42.2 ± 3.0 Mpc (~138 million light-year). NGC 638 was discovered by American astronomer Lewis A. Swift in 1886. NGC 638 has a broad Hydrogen line. NGC 638 is a galaxy whose nucleus shines in the ultraviolet domain. It is listed in the Markarian catalogue under the code Mrk 1003 (MK 1003). To date, two non-redshift measurements give a distance of 55.330 0 ± 1.273 Mpc (~180 million light-year), which is outside the Hubble distance values. Note that the NASA/IPAC database calculates the diameter of a galaxy using the average value of independent measurements, when available, and that consequently the diameter of NGC 638 could be about 11.1 kpc (~36,200 light-year) if the Hubble's law were used to calculate it.

NGC 645 Group NGC 638 is part of the NGC 645 group which includes at least five galaxies. The other three galaxies in this group are NGC 632, UGC 1137 and UGC 1172.

Illustrations

Worked examples

Example 1 — a first encounter with NGC 638

Start with the simplest possible case. Write down what NGC 638 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 638 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 638 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 638

In research: NGC 638 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 638 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 638 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1886, Barred spiral galaxies, Discoveries by Lewis Swift, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 638 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 638 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 638 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 638 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 638 in simple terms?

Why does NGC 638 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 638?

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 638.