astronomy

NGC 3998

NGC 3998 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 3998 rather than just read about it. In short: NGC 3998 is a lenticular galaxy located in the constellation Ursa Major. It was discovered on April 14, 1789, by German-British astronomer William Herschel.

Key takeaways

NGC 3998 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 3998 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 3998 from memory before moving on to harder problems.

Reference excerpt

NGC 3998 is a lenticular galaxy located in the constellation Ursa Major. It was discovered on April 14, 1789, by German-British astronomer William Herschel. At a distance of 45 million light-years (13.7 megaparsecs), it is located relatively nearby, making it a well-studied object. In Gérard de Vaucouleurs' atlas of galaxy morphological types, NGC 3998 has a classification of SA00(r):, meaning it is unbarred and has an internal ring. It is classified as a LINER-type galaxy. As an early-type galaxy, NGC 3998's stars are relatively old and reddish in color, but its nuclear region may still have signs of star formation with stars less than 10 million years old. The galaxy's shape is very round, and also oblate.

Structure NGC 3998 contains an active galactic nucleus, or AGN. These are supermassive black holes that are surrounded by accretion disks that emit large amounts of energy across the electromagnetic spectrum. The supermassive black hole has been modeled to be about 8.1+2.0−1.9×108 M☉ The AGN's power is relatively low, and like most other low-power radio galaxies, most of its emission is concentrated near its core. However, it also has some S-shaped lobes of emission, which are quite young and active, at only a few tens of millions of years old. NGC 3998 has a small disk of ionized Hα radiation that is about roughly 100 parsecs wide, along with a larger, warped disk of neutral hydrogen. It is thought that the gas disk has just started to align with the stellar distribution, which would also explain the warped shape of the radio emission.

NGC 3631 Group According to A.M. Garcia, NGC 3998 is part of the NGC 3631 group (also known as LGG 241). This group includes at least 10 galaxies, including NGC 3631, NGC 3657, NGC 3718, NGC 3729, NGC 3913, NGC 3972, UGC 6251, UGC 6446, and UGC 6816.

See also List of NGC objects (3001–4000)

References

External links Media related to NGC 3998 at Wikimedia Commons

Illustrations

Worked examples

Example 1 — a first encounter with NGC 3998

Start with the simplest possible case. Write down what NGC 3998 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 3998 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 3998 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 3998

In research: NGC 3998 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 3998 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 3998 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1789, Discoveries by William Herschel, IRAS catalogue objects, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 3998 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 3998 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 3998 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 3998 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 3998 in simple terms?

NGC 3998 is a lenticular galaxy located in the constellation Ursa Major. It was discovered on April 14, 1789, by German-British astronomer William Herschel.

Why does NGC 3998 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 3998?

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 3998.