astronomy

Messier 28

Messier 28 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 28 rather than just read about it. In short: Messier 28 or M28, also known as NGC 6626, is a globular cluster of stars in the center-west of Sagittarius. It was discovered by French astronomer Charles Messier in 1764.

Key takeaways

Messier 28 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 28 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Messier 28 from memory before moving on to harder problems.

Reference excerpt

Messier 28 or M28, also known as NGC 6626, is a globular cluster of stars in the center-west of Sagittarius. It was discovered by French astronomer Charles Messier in 1764. He briefly described it as a "nebula containing no star... round, seen with difficulty in 31⁄2-foot telescope; Diam 2′."

Location In the sky it is less than a degree to the northwest of the 3rd magnitude star Kaus Borealis (Lambda Sgr). This cluster is faintly visible as a hazy patch with a pair of binoculars and can be readily found in a small telescope with an 8 cm (3.1 in) aperture, showing as a nebulous feature spanning 11.2 arcminutes. Using an aperture of 15 cm (5.9 in), the core becomes visible and a few distinct stars can be resolved, along the periphery. Larger telescopes will provide greater resolution, one of 25 cm (9.8 in) revealing a dense 2′ core, with more density within. It is about 18,300 light-years away from Earth. It is about 551000 M☉ and its metallicity (averaging −1.32 which means more than 10 times less than our own star), coherency and preponderence of older stellar evolution objects, support its dating to very roughly 12 billion years old. 18 RR Lyrae-type variable stars have been found within.

Discovery It bore the first discovery of a millisecond pulsar in a globular cluster – PSR B1821–24. This was using the Lovell Telescope at Jodrell Bank Observatory, England. A total of 11 further of these have since been detected in it with the telescope at Green Bank Observatory, West Virginia. As of 2011, these number the third-most in a cluster tied to the Milky Way, following Terzan 5 and 47 Tucanae.

Gallery

Illustrations

Worked examples

Example 1 — a first encounter with Messier 28

Start with the simplest possible case. Write down what Messier 28 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 28 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 28 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 28

In research: Messier 28 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 28 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 28 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1764, Discoveries by Charles Messier, Globular clusters, so understanding it makes those chapters shorter.
In everyday life: Look for Messier 28 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 28 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Messier 28 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 28 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Messier 28 in simple terms?

Messier 28 or M28, also known as NGC 6626, is a globular cluster of stars in the center-west of Sagittarius. It was discovered by French astronomer Charles Messier in 1764.

Why does Messier 28 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 28?

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 28.