science

NGC 2158

NGC 2158 is a science 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 2158 rather than just read about it. In short: NGC 2158 is an open cluster of stars in the constellation of Gemini. Alternatively, it may be identified as OCL 468, Lund 206 or Melotte 40.

Key takeaways

NGC 2158 belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect NGC 2158 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 2158 from memory before moving on to harder problems.

Reference excerpt

NGC 2158 is an open cluster of stars in the constellation of Gemini. Alternatively, it may be identified as OCL 468, Lund 206 or Melotte 40. This cluster is located around 11,000 light years (3600 ±400 pc) from Earth. It is about 2 billion years old, making it an intermediate age cluster. The cluster is populous with stars, containing some 3000 ±69 stars within a radius of about 8 light years. It is, in angle, immediately southwest of open cluster Messier 35. The two clusters are unrelated, as the subject is around 9,000 light years further away.

History Once thought to be a globular cluster, it is now known to be a metal-poor open cluster that is a member of the old thin disk population. It was first classed as such by Trumpler, but later Shapley would classify it as an open cluster due to its diffuse core. NGC 2158 has been studied numerous times. A study from Arp & Cuffey (1962) was the first study of NGC 2158. It obtained photographic photometry for about 900 stars and determined the cluster to be an intermediate between regular star clusters and globular clusters. Later, the photometry of more than 2000 stars would be obtained by Karchenko, Andruk & Schilbach (1997).

Properties NGC 2158 has unusual properties for an open cluster (OC). Its rich stellar content and brightness initially makes it appear as a globular cluster (GC): only with suitable equipment can the diffuse nature of the cluster be seen. It also has a red giant population similar to GCs. However it is not a GC, but is rather an intermediate object between globular clusters and regular star clusters. The cluster has anomalously low amount of metals making it metal-poor. It has been estimated that NGC 2158 is around 2 billion years old. This would make the cluster of intermediate-age.

Contents NGC 2158 is a populous cluster with many low to intermediate mass stars. NGC 2158 has three mass regimes: high mass stars, low mass stars and very low mass stars. Data used from the third edition of the Gaia Data Release (DR3) revealed that there are 3067 ±69.84 stars totaling to a mass of 3216.4 ±59.50 solar masses. There is a red giant population. The cluster also has a M-dwarf discontinuity. It also contains a cataclysmic variable (CV) star (the fourth known to exist in an open cluster) and five Delta Scuti variables (δ Scuti). Due to the distance of NGC 2158, most binary systems that survived inside the dense environment are unable to be resolved. Instead, these systems appear as point-like sources with the exception of wide binary systems which can be resolved as two distinct sources.

Additional images

References

External links Media related to NGC 2158 at Wikimedia Commons NGC 2158 (SEDS)

NGC 2158 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images NASA Astronomy Picture of the Day: Open Star Clusters M35 and NGC 2158 (2003 December 15)

Illustrations

Worked examples

Example 1 — a first encounter with NGC 2158

Start with the simplest possible case. Write down what NGC 2158 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 2158 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 2158 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 2158

In research: NGC 2158 appears in science 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 2158 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 2158 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Gemini (constellation), NGC objects, Open clusters, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 2158 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 2158 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 2158 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 2158 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 2158 in simple terms?

NGC 2158 is an open cluster of stars in the constellation of Gemini. Alternatively, it may be identified as OCL 468, Lund 206 or Melotte 40.

Why does NGC 2158 matter?

Because it connects several science 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 2158?

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 2158.