astronomy

NGC 691

NGC 691 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 691 rather than just read about it. In short: NGC 691 is an unbarred spiral galaxy located in the constellation Aries. It is located at a distance of circa 120 million light years from Earth, which, given its apparent dimensions, means that NGC 691 is about 130,000 light years across.

Key takeaways

NGC 691 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 691 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 691 from memory before moving on to harder problems.

Reference excerpt

NGC 691 is an unbarred spiral galaxy located in the constellation Aries. It is located at a distance of circa 120 million light years from Earth, which, given its apparent dimensions, means that NGC 691 is about 130,000 light years across. It was discovered by William Herschel on November 13, 1786. NGC 691 features a multiple ring structure, with three rings recognised in the infrared, with diameters of 1.03, 1.67, and 2.79 arcminutes. When imaged in H-alpha, the galaxy appears patchy. The total star formation rate of the galaxy is estimated to be about 0.6 M☉ per year.

NGC 691 Group NGC 691 is the foremost member of a galaxy group known as the NGC 691 group. Other members of the group include IC 163, NGC 678, NGC 680, NGC 694, IC 167, and NGC 697.

Supernova One supernova has been observed in NGC 691. SN 2005W was discovered by Yoji Hirose in unfiltered CCD frames taken on Feb. 1.442 UT with a 0.35-m f/6.8 Schmidt-Cassegrain reflector. The supernova was located 56" east and 1" south of the center of NGC 691 and at the time of the discovery had an apparent magnitude of 15.2. Spectrographic observations indicated it was a Type Ia supernova about a week before maximum. The peak magnitude of the supernova was 14.3, on February 10.759.

Gallery

References

External links Media related to NGC 691 at Wikimedia Commons NGC 691 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images NGC 691 on SIMBAD

Illustrations

Worked examples

Example 1 — a first encounter with NGC 691

Start with the simplest possible case. Write down what NGC 691 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 691 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 691 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 691

In research: NGC 691 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 691 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 691 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aries (constellation), Astronomical objects discovered in 1786, Discoveries by William Herschel, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 691 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 691 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 691 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 691 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 691 in simple terms?

Why does NGC 691 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 691?

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 691.