astronomy

Messier 39

Messier 39 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 Messier 39 rather than just read about it. In short: Messier 39 or M39, also known as NGC 7092, is an open cluster of stars in the constellation of Cygnus, sometimes referred to as the Pyramid Cluster. It is positioned two degrees south of the star Pi Cygni and around 9° east-northeast of Deneb.

Key takeaways

Messier 39 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Messier 39 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Messier 39 from memory before moving on to harder problems.

Reference excerpt

Messier 39 or M39, also known as NGC 7092, is an open cluster of stars in the constellation of Cygnus, sometimes referred to as the Pyramid Cluster. It is positioned two degrees south of the star Pi Cygni and around 9° east-northeast of Deneb. The cluster was discovered by Guillaume Le Gentil in 1749, then Charles Messier added it to his catalogue in 1764. When observed in a small telescope at low power the cluster shows around two dozen members but is best observed with binoculars. It has a total integrated magnitude (brightness) of 4.6 and spans an angular diameter of 29 arcminutes – about the size of the full Moon. It is centered about 1,010 light-years (311 parsecs) away. This cluster has an estimated mass of 232 M☉ and a linear tidal radius of 8.6±1.8 pc. Of the 15 brightest components, six form binary star systems; one more is suspected. HD 205117 is a probable eclipsing binary system with a period of 113.2 days that varies by 0.051 in visual magnitude. Both members seem to be subgiants. Within are at least five chemically peculiar stars and ten suspected short-period variable stars.

Map

Illustrations

Worked examples

Example 1 — a first encounter with Messier 39

Start with the simplest possible case. Write down what Messier 39 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 Messier 39 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 Messier 39 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 Messier 39

In research: Messier 39 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 Messier 39 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: Messier 39 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1764, Cygnus (constellation), Messier objects, so understanding it makes those chapters shorter.
In everyday life: Look for Messier 39 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 Messier 39 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Messier 39 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 Messier 39 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Messier 39 in simple terms?

Why does Messier 39 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 Messier 39?

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 Messier 39.