astronomy

NGC 4138

NGC 4138 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 4138 rather than just read about it. In short: NGC 4138 is the New General Catalogue identifier for a lenticular galaxy in the northern constellation of Canes Venatici. Located around 52 million light years from Earth, it spans some 2.1 × 1.3 arc minutes and has an apparent visual magnitude of 11.3.

Key takeaways

NGC 4138 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 4138 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 4138 from memory before moving on to harder problems.

Reference excerpt

NGC 4138 is the New General Catalogue identifier for a lenticular galaxy in the northern constellation of Canes Venatici. Located around 52 million light years from Earth, it spans some 2.1 × 1.3 arc minutes and has an apparent visual magnitude of 11.3. The morphological classification of NGC 4138 is SA0+(r), indicating it lacks a bar formation and has tightly wound spiral arms with a ring-like structure around the nucleus. It has no nearby companion galaxies. This is a Seyfert 1.9 galaxy with an active galactic nucleus, having radio emissions detected in its nuclear region. Two radio sources have been detected, with the eastern component being the brighter at 1.0 mJy while the fainter source is emitting 0.75 mJy. This radiation is most likely coming from jets of energetic material being ejected by a central black hole. In 1996 it was revealed that this galaxy has a counter-rotating disk; around 20% of the stars in the galaxy are rotating in the opposite direction from the other 80%. The neutral and ionized gas in this galaxy are rotating in the same direction as the counter-rotating disk, and the stars in this group are generally younger than the main stellar population. This disk may have formed as the result of a merger with a gas-rich dwarf galaxy some four billion years ago. Simulations indicate that the counter-rotation of this disk is acting to suppress spiral arm features in the galaxy as a whole. The young, star-forming ring structure is likely the result of collisions between gas clouds rotating in the opposite directions. NGC 4138 is a member of the NGC 4111 Group, which is part of the Ursa Major Cloud and is the second largest group in the cloud after the NGC 3992 Group.

Gallery

References

External links Media related to NGC 4138 at Wikimedia Commons

Illustrations

Worked examples

Example 1 — a first encounter with NGC 4138

Start with the simplest possible case. Write down what NGC 4138 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 4138 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 4138 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 4138

In research: NGC 4138 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 4138 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 4138 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Canes Venatici, Lenticular galaxies, NGC 4111 Group, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 4138 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 4138 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 4138 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 4138 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 4138 in simple terms?

Why does NGC 4138 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 4138?

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 4138.