astronomy

NGC 4157

NGC 4157 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 4157 rather than just read about it. In short: NGC 4157 is a spiral galaxy in the constellation Ursa Major. The galaxy lies about 55 million light years away from Earth, which means, given its apparent dimensions, that NGC 4157 is approximately 125,000 light years across.

Key takeaways

NGC 4157 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 4157 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 4157 from memory before moving on to harder problems.

Reference excerpt

NGC 4157 is a spiral galaxy in the constellation Ursa Major. The galaxy lies about 55 million light years away from Earth, which means, given its apparent dimensions, that NGC 4157 is approximately 125,000 light years across. It was discovered by William Herschel on March 9, 1788.

Characteristics NGC 4157 seen nearly edge-on, with an inclination of 84° based on CO imaging. The total stellar mass of NGC 4157 is (2.92±0.04)×1010 M☉, while the dust mass is estimated to be 2.1×107 M☉. The hydrogen disk of NGC 4157 is symmetric and slightly wrapped, indicating no strong interaction with other galaxies, and extends to twice the size of the optical disk. The total HI mass in the galaxy is estimated to be 109.72 M☉. The star formation rate of the galaxy is 1.76±0.18 M☉ per year. A star formation area is visible beyond the end of the optical disk and is also visible in X-ray and ultraviolet imaging. It could probably be the result of a recent accretion. The galaxy has radio emission extending above and below the optical disk, indicating the presence of a radio halo. There is also radio emission extending southwards from the north-eastern end of the disk.

Supernovae Three supernovae have been observed in NGC 4157:

SN 1937A (type unknown, mag. 16.2) was discovered by Fritz Zwicky on 16 February 1937. SN 1955A (type unknown, mag. 16) was discovered by Fritz Zwicky on 14 April 1955. SN 2003J (Type II, mag. 16.7) was discovered by R. Kushida, Tim Puckett, and Jack Newton on 11 January 2003.

Nearby galaxies NGC 4157 is the foremost galaxy of the NGC 4157 Group. Other members of the group include NGC 4085, NGC 4088, UGC 6992, and UGC 7176. UGC 7176 is a companion of NGC 4157, lying 12 arcminutes away. The group is part of the Ursa Major Cluster, a large association of mostly spiral galaxies lying north of the Virgo Cluster, that is part of the Local Supercluster. NGC 4157 is one of the dominant galaxies in the cluster, along with NGC 3769, NGC 3877, NGC 3992, NGC 4111, NGC 4217 and NGC 4346.

References

External links

NGC 4157 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 4157

Start with the simplest possible case. Write down what NGC 4157 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 4157 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 4157 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 4157

In research: NGC 4157 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 4157 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 4157 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1788, Discoveries by William Herschel, IRAS catalogue objects, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 4157 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 4157 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 4157 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 4157 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 4157 in simple terms?

Why does NGC 4157 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 4157?

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 4157.