astronomy

NGC 4665

NGC 4665 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 4665 rather than just read about it. In short: NGC 4665, also catalogued as NGC 4624 and NGC 4664, is a barred lenticular or spiral galaxy located in the constellation Virgo. It is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster.

Key takeaways

NGC 4665 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 4665 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 4665 from memory before moving on to harder problems.

Reference excerpt

NGC 4665, also catalogued as NGC 4624 and NGC 4664, is a barred lenticular or spiral galaxy located in the constellation Virgo. It is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster. It is located at a distance of circa 60 million light years from Earth, which, given its apparent dimensions, means that NGC 4665 is about 75,000 light years across. NGC 4665 lies 2 and 3/4 degrees east-south east of Delta Virginis and 50 arcminutes southwest of 35 Virginis. It can be viewed through a moderately sized telescope with 23x magnification, forming a pair with an 11th magnitude star 1.5 arcminutes southwest. It is part of the Herschel 400 Catalogue.

Observation history It was discovered by William Herschel on February 23, 1784, however, he noted a location 10 arcminutes off the galaxy, where there is no object. It was observed by William Herschel again on April 30, 1786, noting the correct coordinates, and he misidentified it as another nebula. The fact that they are the same object was noted by John Louis Emil Dreyer in 1912 in the corrections of the New General Catalogue. It was also recorded independently on April 9, 1828 by John Herschel.

Physical characteristics NGC 4665 has a luminous, slightly elliptical bulge and a prominent bar with high surface brightness. The isophotes appear boxy at the end of the bar. The total bar length is estimated to be near 3 kpc. The bar is slightly twisted, turning near 12 degrees along its axis. Two diffuse, faint arms emerge from each side of the bar and form a pseudoring. The surface brightness of the arms is higher near the bar. The southern arm appears a bit stronger. An arch feature is observed at the east side of the galaxy that could be a partial outer dusty ring. The outer isophotes are elliptical. The total mass of molecular gas is less than 107.3 M☉. NGC 4665 belongs to the NGC 4636 group. Other members of the group include NGC 4457, NGC 4586, NGC 4587, NGC 4600, NGC 4636, and NGC 4688. These galaxies, along with NGC 4753, Messier 61 and their groups form the southern boundary of the Virgo Cluster. It can be difficult to determine which galaxies belong to which group, especially around the southern edge of the Virgo cluster where there is a confusion of galaxies at different distances.

References

External links

NGC 4665 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images NGC 4665 on SIMBAD

Illustrations

Worked examples

Example 1 — a first encounter with NGC 4665

Start with the simplest possible case. Write down what NGC 4665 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 4665 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 4665 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 4665

In research: NGC 4665 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 4665 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 4665 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1784, Barred lenticular galaxies, Barred spiral galaxies, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 4665 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 4665 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 4665 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 4665 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 4665 in simple terms?

Why does NGC 4665 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 4665?

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 4665.