astronomy

Messier 71

Messier 71 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 71 rather than just read about it. In short: Messier 71 (also known as M71, NGC 6838, or the Angelfish Cluster) is a globular cluster in the small northern constellation Sagitta. It was discovered by Philippe Loys de Chéseaux in 1745 and included by Charles Messier in his catalog of non-comet-like objects in 1780.

Key takeaways

Messier 71 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 71 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Messier 71 from memory before moving on to harder problems.

Reference excerpt

Messier 71 (also known as M71, NGC 6838, or the Angelfish Cluster) is a globular cluster in the small northern constellation Sagitta. It was discovered by Philippe Loys de Chéseaux in 1745 and included by Charles Messier in his catalog of non-comet-like objects in 1780. It was also noted by Koehler at Dresden around 1775. Messier 71 is also known as NGC 6839, though this identification is very uncertain. This star cluster is about 13,000 light years away from Earth and spans 27 light-years (8 pc). The irregular variable star Z Sagittae is a member.

M71 was for many decades thought (until the 1970s) to be a densely packed open cluster and was classified as such by leading astronomers in the field of star cluster research due to its lacking a dense central compression, and to its stars having more "metals" than is usual for an ancient globular cluster; furthermore, it lacks the RR Lyrae "cluster" variable stars that are common in most globular clusters. However, modern photometric photometry has detected a short "horizontal branch" in the H–R diagram (chart of temperature versus luminosity) which is characteristic of a globular cluster. The shortness of the branch explains the lack of RR Lyrae variables and is due to the globular cluster's relatively young age of 9–10 billion years. Taking in many or only late series (Population I) stars explains relatively its stars. Hence today M71 is designated as a very loosely concentrated globular cluster, much like M68 in Hydra. M71 has a mass of about 53,000 M☉ and a luminosity of around 19,000 L☉.

See also List of Messier objects NGC 6366 NGC 6342

References

Gallery

External links

Messier 71 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images Messier71 @ SEDS Messier pages Messier 71, Galactic Globular Clusters Database page Messier 71, LRGB CCD image based on two hours total exposure Messier 71: an Unusual Globular Cluster, ESA\Hubble picture of the week. McCormac, James; Szymanek, Nik. "M71 – Globular Cluster". Deep Sky Videos. Brady Haran.

Illustrations

Worked examples

Example 1 — a first encounter with Messier 71

Start with the simplest possible case. Write down what Messier 71 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 71 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 71 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 71

In research: Messier 71 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 71 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 71 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1745, Globular clusters, Messier objects, so understanding it makes those chapters shorter.
In everyday life: Look for Messier 71 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Messier 71 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Messier 71 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 71 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Messier 71 in simple terms?

Why does Messier 71 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 71?

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 71.