astronomy

Messier 72

Messier 72 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 72 rather than just read about it. In short: Messier 72 (also known as M72 or NGC 6981) is a globular cluster in the south west of the southern constellation of Aquarius. Observational history M72 was discovered by astronomer Pierre Méchain on August 29 1780.

Key takeaways

Messier 72 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 72 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Messier 72 from memory before moving on to harder problems.

Reference excerpt

Messier 72 (also known as M72 or NGC 6981) is a globular cluster in the south west of the southern constellation of Aquarius.

Observational history M72 was discovered by astronomer Pierre Méchain on August 29 1780. His countryman Charles Messier looked for it 36 days later, and included it in his catalog. Both opted for the then-dominant of the competing terms for such objects, considering it a faint nebula rather than a cluster. With a larger instrument, astronomer John Herschel called it a bright "cluster of stars of a round figure". Astronomer Harlow Shapley noted a similarity to Messier 4 and 12. It is visible in a good night sky as a faint nebula in a telescope with a 6 cm (2.4 in) aperture.

Properties Based upon a 2011 census of variable stars, the cluster is 54,500 light-years (16,700 pc) away from the Sun. It has an estimated combined mass of 168,000 solar masses (M☉), and is around 9.5 billion years old. There are 43 identified variable stars in the cluster.

Illustrations

Worked examples

Example 1 — a first encounter with Messier 72

Start with the simplest possible case. Write down what Messier 72 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 72 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 72 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 72

In research: Messier 72 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 72 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 72 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aquarius (constellation), Astronomical objects discovered in 1780, Discoveries by Pierre Méchain, so understanding it makes those chapters shorter.
In everyday life: Look for Messier 72 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 72 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Messier 72 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 72 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Messier 72 in simple terms?

Messier 72 (also known as M72 or NGC 6981) is a globular cluster in the south west of the southern constellation of Aquarius. Observational history M72 was discovered by astronomer Pierre Méchain on August 29 1780.

Why does Messier 72 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 72?

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 72.