astronomy

IC 2391

IC 2391 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 2391 rather than just read about it. In short: IC 2391 (also known as the Omicron Velorum Cluster or Caldwell 85) is an open cluster in the constellation Vela consisting of hot, young, blueish stars, some of which are binaries and one of which is a quadruple. Persian astronomer Abd al-Rahman al-Sufi first described it as "a nebulous star" in c. 964.

Key takeaways

IC 2391 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 2391 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of IC 2391 from memory before moving on to harder problems.

Reference excerpt

IC 2391 (also known as the Omicron Velorum Cluster or Caldwell 85) is an open cluster in the constellation Vela consisting of hot, young, blueish stars, some of which are binaries and one of which is a quadruple. Persian astronomer Abd al-Rahman al-Sufi first described it as "a nebulous star" in c. 964. It was re-found by Abbe Lacaille and cataloged as Lac II 5.

Description IC 2391 is centred about 490 light-years away from Earth and can be seen with the naked eye. It contains about 30 stars with a total visual magnitude of 2.5, spread out across 50 arcminutes.

Member stars These are some of the prominent members of IC 2391:

The stars' era of formation is similar to open cluster IC 2602 in neighbouring Carina, and has a lithium depletion boundary age of about 50 million years. The latter group averages about the same distance, placed at about 485 light years away.

Argus Association The components formed at about the same time as a nearer group, known as the "Argus Association" which one motion model suggests began in their own nebula cloud. These are in a similar direction, roughly the Vela constellation, within the local galactic arm. The supposed association may chiefly comprise:

References

External links

Frommert, Harmut (29 March 1998). "Omicron Velorum (IC 2391)". SEDS Messier Database. Students for the Exploration and Development of Space.

IC 2391 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images "IC 2391". SIMBAD. Centre de données astronomiques de Strasbourg. "Open Cluster". An Atlas of The Universe.

Illustrations

Worked examples

Example 1 — a first encounter with IC 2391

Start with the simplest possible case. Write down what IC 2391 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 2391 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 2391 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 2391

In research: IC 2391 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 2391 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 2391 is common in secondary-school and first-year university syllabi. It links to neighbouring topics 10th century in science, Astronomical objects discovered in the Middle Ages, Caldwell objects, so understanding it makes those chapters shorter.
In everyday life: Look for IC 2391 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 2391 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what IC 2391 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 2391 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is IC 2391 in simple terms?

Why does IC 2391 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 2391?

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 2391.