astronomy

NGC 404

NGC 404 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 404 rather than just read about it. In short: NGC 404 is a field galaxy located about 10 million light years away in the constellation Andromeda. It was discovered by William Herschel in 1784, and is visible through small telescopes.

Key takeaways

NGC 404 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 404 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 404 from memory before moving on to harder problems.

Reference excerpt

NGC 404 is a field galaxy located about 10 million light years away in the constellation Andromeda. It was discovered by William Herschel in 1784, and is visible through small telescopes. NGC 404 lies just beyond the Local Group and does not appear gravitationally bound to it. It is located within 7 arc-minutes of second magnitude star Mirach, making it a difficult target to observe or photograph and granting it the nickname "Mirach's Ghost".

Physical characteristics NGC 404 is a very isolated dwarf lenticular galaxy, a bit more luminous and smaller than the Small Magellanic Cloud. Unlike many other early-type galaxies, it is very rich in neutral hydrogen, most of it concentrated in a pair of large rings around it. It also has star formation both in its center and in its outermost regions, albeit at a low level. Both the outer gas disk and its star formation are assumed to have been triggered by one or several mergers with smaller galaxies roughly 1 billion years ago and it has been proposed NGC 404 is a former spiral galaxy that was transformed into a lenticular one by that event.

LINER emission NGC 404 contains a low-ionization nuclear emission-line region (LINER), a type of region that is characterized by spectral line emission from weakly ionized atoms. A nuclear star cluster is also present as well as (likely) a supermassive black hole, with a mass of several tens of thousands solar masses.

Distance measurements At least two techniques have been used to measure distances to NGC 404. The infrared surface brightness fluctuations distance measurement technique estimates distances to spiral galaxies based on the graininess of the appearance of their bulges. The distance measured to NGC 404 using this technique in 2003 is 9.9 ± 0.5 Mly (3.03 ± 0.15 Mpc). However, NGC 404 is close enough that red supergiants can be imaged as individual stars. The light from these stars and knowledge of how they should compare to nearby stars within the Milky Way galaxy allows for direct measurement of the distance to the galaxy. This method is referred to as the tip of the red giant branch (TRGB) method. The estimated distance to NGC 404 using this technique is 10.0 ± 1.2 Mly (3.1 ± 0.4 Mpc). Averaged together, these distance measurements give a distance estimate of 10.0 ± 0.7 Mly (3.07 ± 0.21 Mpc).[a]

Possible satellite In 2018 a possible satellite designated Donatiello I was identified. Donatiello I is a dwarf spheroidal galaxy with little recent star formation. Difficulty in establishing the exact distance to the galaxy leaves its status as a satellite unconfirmed.

Gallery

Notes

References

External links

Encyclopedia of Astrobiology, Astronomy & Spaceflight Entry Curdridge Observatory article NASA Astronomy Picture of the Day: NGC 404: Mirach's Ghost (29 October 2008)

NGC 404 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 404

Start with the simplest possible case. Write down what NGC 404 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 404 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 404 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 404

In research: NGC 404 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 404 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 404 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Andromeda (constellation), Astronomical objects discovered in 1784, Discoveries by William Herschel, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 404 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 404 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 404 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 404 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 404 in simple terms?

NGC 404 is a field galaxy located about 10 million light years away in the constellation Andromeda. It was discovered by William Herschel in 1784, and is visible through small telescopes.

Why does NGC 404 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 404?

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 404.