astronomy

NGC 1667

NGC 1667 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 1667 rather than just read about it. In short: NGC 1667, also catalogued as NGC 1689, is a spiral galaxy located in the constellation Eridanus. It is located at a distance of about 150 million light years from Earth based on redshift-independent methods, which, given its apparent dimensions, means that NGC 1667 is about 80,000 light years across.

Key takeaways

NGC 1667 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 1667 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 1667 from memory before moving on to harder problems.

Reference excerpt

NGC 1667, also catalogued as NGC 1689, is a spiral galaxy located in the constellation Eridanus. It is located at a distance of about 150 million light years from Earth based on redshift-independent methods, which, given its apparent dimensions, means that NGC 1667 is about 80,000 light years across. Based on its redshift, the galaxy sits roughly 200 million light years away from the Sun. It was discovered by Édouard Stephan on December 13, 1884, and independently by Lewis Swift on October 22, 1886.

Characteristics The galaxy has a small, bright nucleus with a weak bar. There is dust in the inner region of the galaxy, forming a nuclear spiral. Multiple spiral arms are visible near the nucleus, with are roughly symmetrical but the centre of symmetry is offset from the nucleus. The galaxy has an inner ring with many knots measuring 0.33 by 0.24 arcminutes. The ring is composed of many spiral fragments and young star clusters. Three spiral arms emerge from the ring. Many HII regions are visible across the arms and the inner ring. The star formation rate of the galaxy is estimated to be 6.91 M☉ per year.

Active nucleus The nucleus of the galaxy has been found to be active and it has been characterised as a type 2 Seyfert galaxy based on its emission lines. 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 1667 is estimated to be 107.8 (60 million) M☉. Although the nucleus emits ultraviolet, radio waves and H-alpha, it isn't a strong source when compared with the rest of the galaxy. The nucleus accounts for about 5% of the H-alpha emission of the galaxy. The nucleus is surrounded by extended HII regions, with signs of photoionization by hot OB stars, indicative of high star formation rate in central region of the galaxy. There are also large amounts of dust. The nucleus also emitted mostly soft X-rays at a low flux and with little short-term variability in 2004, but with a significant long-term drop in flux between 1977–78 and 2004. In the centre of the galaxy there are two peaks of CO(2-1) emission, two arcseconds across. The western peak lies at the kinematic centre of the galaxy. The inner two arcseconds of the galaxy are rotating at an angle of 150° with respect to the rest of the galaxy, indicating its core is counter-rotating, probably as a result of a merger or gas inflows. The spectrographic study of the nuclear region revealed a nuclear outflow and a gas disk which is twisted by the outflow in the inner arcsecond and gas inflowing from the spiral appear farther from the nucleus. The ionized gas mass outflow rate is estimated to be about 0.16 M☉ per year, while the gas inflow is about 2.8 M☉ per year about 800 parsec from the nucleus. However, most of the inflowing gas will probably not reach the nucleus and accumulate around it, leading to circumnuclear star formation.

Supernova One supernova has been observed in NGC 1667. SN 1986N was discovered on 11 December 1986, with an apparent magnitude of 15, by Carlton R. Pennypacker and others at the Leuschner Observatory. It was located 15" west and 7" south of the centre of the galaxy. Based on its spectrum it was categorised as a Type Ia supernova about 20 days post maximum light.

Nearby galaxies NGC 1667 is a member of the NGC 1667 Group, also known as LGG 118. Other members of the group includes the galaxies IC 387, NGC 1645, NGC 1659, MCG -1-13-12, IC 2101, and IC 2097. NGC 1667 forms a non-interacting pair with NGC 1666, which lies 15 arcminutes away.

Gallery

References

External links

NGC 1667 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images NGC 1667 on SIMBAD

Illustrations

Worked examples

Example 1 — a first encounter with NGC 1667

Start with the simplest possible case. Write down what NGC 1667 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 1667 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 1667 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 1667

In research: NGC 1667 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 1667 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 1667 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1884, Discoveries by Édouard Stephan, Eridanus (constellation), so understanding it makes those chapters shorter.
In everyday life: Look for NGC 1667 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 1667 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 1667 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 1667 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 1667 in simple terms?

Why does NGC 1667 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 1667?

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 1667.