astronomy

NGC 2420

NGC 2420 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 2420 rather than just read about it. In short: NGC 2420 is an open cluster of stars in the constellation of Gemini. It was discovered by German-British astronomer William Herschel on 19 November 1783.

Key takeaways

NGC 2420 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 2420 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 2420 from memory before moving on to harder problems.

Reference excerpt

NGC 2420 is an open cluster of stars in the constellation of Gemini. It was discovered by German-British astronomer William Herschel on 19 November 1783. The cluster is about two billion years old and it is located 10,000 light years away.

Observation

NGC 2420 lies about 6,5 degrees south-southeast of the star Pollux and a bit over two degrees east-northeast of the Eskimo Nebula. Through a small telescope at low magnification it appears as a uniform ghostly light that gets brighter to the centre, similar to a tail-less comet and at x33 magnification some individual stars can be glimpsed with averted vision. At higher magnification the cluster is resolved into a rich field of individual stars. It is included in the Herschel 400 Catalogue.

Characteristics The cluster is located at a greater distance from the galactic centre than the Sun, lying in the direction of the galactic anti-centre, and lies 19° above the galactic plane, which corresponds to a distance of 3,000 light years. It has a Trumpler classification of I1r, indicating a rich detached cluster with a central concentration made out of stars of similar apparent magnitude. Photographic photometry down to magnitude 19 indicates that the cluster has over 500 members, with the brightest being of 11th magnitude. The total number of members is estimated to be around 1,000 within a diameter of 30 light years. It is estimated that 41% of the stars of the cluster are binaries. The cluster has been found to contain two binary systems made out of two blue stragglers, while a third binary system is made out of a blue straggler and an extremely low mass white dwarf. These binary stars shine bright in far ultraviolet. Using data from the Hubble Space Telescope, von Hippel and Gilmore detected eight white dwarf candidates and estimated a cooling age of about 2 billion years. The metallicity of the cluster has been a subject of many studies and has been found to be a bit sub-solar, with a metallicity of -0.26 according to WEBDA. The cluster was found to be a bit metal poor, with a [Fe/H] of -0.7 to -0.6 from spectrographic studies performed in the 1980s while subsequent CCD photometry indicates of a higher metallicity of about -0.30. Pancino et al. indicated a [Fe/H]= -0.05 ± 0.03 according to Pancino et al., which is close to the trend of metallicity descreasing with increasing distance from the galactic centre. The red giants of the cluster have a mean metallicity of −0.16 ± 0.04. Based on spectrographic data of the Gaia-ESO survey, the stars around the turnoff point have sub-solar metallicities but they increase for stars of smaller mass. The stars of the cluster have homogenous CN and CH molecular band strengths. Similar low dispersion was observed in other elements.

See also Messier 67 - a similar old open cluster

References

External links

NGC 2420 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 2420

Start with the simplest possible case. Write down what NGC 2420 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 2420 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 2420 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 2420

In research: NGC 2420 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 2420 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 2420 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1783, Discoveries by William Herschel, Gemini (constellation), so understanding it makes those chapters shorter.
In everyday life: Look for NGC 2420 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 2420 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 2420 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 2420 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 2420 in simple terms?

NGC 2420 is an open cluster of stars in the constellation of Gemini. It was discovered by German-British astronomer William Herschel on 19 November 1783.

Why does NGC 2420 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 2420?

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 2420.