astronomy

IC 4397

IC 4397 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 IC 4397 rather than just read about it. In short: IC 4397 is a spiral galaxy in the constellation of Boötes. Its velocity with respect to the cosmic microwave background is 4,627±16 km/s, which corresponds to a Hubble distance of 222.6 ± 15.6 Mly (68.25 ± 4.78 Mpc).

Key takeaways

IC 4397 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect IC 4397 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of IC 4397 from memory before moving on to harder problems.

Reference excerpt

IC 4397 is a spiral galaxy in the constellation of Boötes. Its velocity with respect to the cosmic microwave background is 4,627±16 km/s, which corresponds to a Hubble distance of 222.6 ± 15.6 Mly (68.25 ± 4.78 Mpc). It was discovered by French astronomer Guillaume Bigourdan on 23 June 1889. IC 4397 has an active galactic nucleus, i.e. it has a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars. It is a Seyfert II galaxy, i.e. it has a quasar-like nucleus with very high surface brightness, whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, the host galaxy is clearly detectable. The nucleus also shines brightly in the ultraviolet. IC 4397 is listed in the Markarian catalogue as Mrk 1510.

NGC 5653 group According to A. M. Garcia, IC 4397 is part of the NGC 5653 group (also known as LGG 383). This group of galaxies has at least 15 members, including NGC 5629, NGC 5635, NGC 5639, NGC 5641, NGC 5642, NGC 5653, NGC 5659, NGC 5657, NGC 5672, NGC 5703, NGC 5735, UGC 9253, UGC 9268, and UGC 9302.

Supernovae Three supernovae have been observed in IC 4397:

SN 2018dbg (Type Ib/Ic, mag. 18.43) was discovered by the Zwicky Transient Facility on 28 June 2018. SN 2019hyk (Type II, mag. 16.5) was discovered by ASAS-SN on 22 June 2019. SN 2025afdy (Type Ia, mag. 16.003) was discovered by ATLAS on 27 November 2025.

Illustrations

Worked examples

Example 1 — a first encounter with IC 4397

Start with the simplest possible case. Write down what IC 4397 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 IC 4397 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 IC 4397 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 IC 4397

In research: IC 4397 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 IC 4397 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: IC 4397 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1889, Boötes, Discoveries by Guillaume Bigourdan, so understanding it makes those chapters shorter.
In everyday life: Look for IC 4397 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 IC 4397 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what IC 4397 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 IC 4397 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is IC 4397 in simple terms?

Why does IC 4397 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 IC 4397?

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 IC 4397.