astronomy

NGC 931

NGC 931 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 931 rather than just read about it. In short: NGC 931 is a spiral galaxy located in the constellation Triangulum. It is located at a distance of circa 200 million light-years from Earth, which, given its apparent dimensions, means that NGC 931 is about 200,000 light years across.

Key takeaways

NGC 931 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 931 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 931 from memory before moving on to harder problems.

Reference excerpt

NGC 931 is a spiral galaxy located in the constellation Triangulum. It is located at a distance of circa 200 million light-years from Earth, which, given its apparent dimensions, means that NGC 931 is about 200,000 light years across. It was discovered by Heinrich d'Arrest on September 26, 1865. It is classified as a Seyfert galaxy.

Characteristics

The nucleus of NGC 931 has been found to be active and it has been categorised as a type I Seyfert galaxy due to its narrow H-beta emission line. The most accepted theory for the energy source of active galactic nuclei is the presence of an accretion disk around a supermassive black hole. The mass of the black hole in the centre of NGC 931 is estimated to be 107.64 ± 0.40 (17- 110 million) M☉ based on the stellar velocity dispersion. NGC 931 has been found to emit radiowaves, ultraviolet and X-rays. Observations by ASCA revealed the X-ray spectrum was composed of soft and hard emission. The hard element was identified as a strong and wide fluorescent FeKa line, which is created when X-rays meet an optically cold thick material. The soft element has been identified as warm absorbing material. The galaxy was further observed by XMM-Newton, where it was observed that there were significant fluctuations and time lags in the flux changes observed both in the soft and hard elements. A detail X-ray spectrum of NGC 931 was obtained by Chandra X-ray Observatory. It revealed the presence of many absorption lines from neon, magnesium, and silicon, with a variety of ionisation states. These lines were attributed to low ionisation gases surrounding the nuclear X-ray source. No significant outflowing gas was detected in the large scale.

Supernova One supernova has been observed in NGC 931. SN 2009lw was discovered by W. Li, S. B. Cenko, and A. V. Filippenko during the Lick Observatory Supernova Search on 24.24 November 2009, when it had an apparent magnitude of 18.8. It was identified as a Type-Ib or possibly a Type-IIb supernova a few months past maximum light.

Nearby galaxies NGC 931 has been identified as a member of the NGC 973 group, one of the largest galaxy groups of the Perseus–Pisces Supercluster, with at least 39 galaxies identified as its members. Other members of the group include NGC 917, NGC 940, NGC 969, NGC 973, NGC 974, NGC 978, NGC 987, NGC 983, NGC 1060, NGC 1066, NGC 1067, and UGC 2105. On the other hand, Garcia recognised NGC 931 as the largest galaxy in a galaxy group known as the NGC 931 group, which also included NGC 940. A smaller companion galaxy, PGC 212995, measuring 0.2 by 0.1 arcminutes, is superimposed on the galaxy, lying about 0.35 arcminutes towards the north.

See also NGC 1532 - a similar spiral galaxy

References

External links

NGC 931 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images NGC 931 on SIMBAD

Illustrations

Worked examples

Example 1 — a first encounter with NGC 931

Start with the simplest possible case. Write down what NGC 931 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 931 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 931 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 931

In research: NGC 931 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 931 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 931 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1865, Discoveries by Heinrich Louis d'Arrest, Markarian galaxies, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 931 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 931 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 931 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 931 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 931 in simple terms?

Why does NGC 931 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 931?

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 931.