astronomy

Messier 92

Messier 92 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 92 rather than just read about it. In short: Messier 92 (also known as M92, M 92, or NGC 6341) is a globular cluster of stars in the northern constellation of Hercules. Discovery It was discovered by Johann Elert Bode on December 27, 1777, then published in the Berliner Astronomisches Jahrbuch during 1779.

Key takeaways

Messier 92 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 92 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Messier 92 from memory before moving on to harder problems.

Reference excerpt

Messier 92 (also known as M92, M 92, or NGC 6341) is a globular cluster of stars in the northern constellation of Hercules.

Discovery It was discovered by Johann Elert Bode on December 27, 1777, then published in the Berliner Astronomisches Jahrbuch during 1779. It was inadvertently rediscovered by Charles Messier on March 18, 1781, and added as the 92nd entry in his catalogue. William Herschel first resolved individual stars in 1783.

Visibility It is one of the brighter of its sort in apparent magnitude in the northern hemisphere and in its absolute magnitude in the galaxy, but it is often overlooked by amateur astronomers due to angular proximity to bright cluster Messier 13, about 20% closer. Though when compared to M13, M92 is only slightly less bright, but about 1/3 less extended. It is visible to the naked eye under very good viewing conditions. With a small telescope, M92 can be seen as a nebulous smudge even in a severely light-polluted sky, and can be further resolved in darker conditions.

Characteristics It is also one of the galaxy's oldest clusters. It is around 16×10^3 ly (4.9 kpc) above/below the galactic plane and 33×10^3 ly (10 kpc) from the Galactic Center. It is about 26,700 light-years away from the Solar System.The half-light radius, or radius containing the upper half of its light emission, is 1.09 arcminutes (′), while the tidal radius, the broadest standard measure, is 15.17′. It appears only slightly flattened: its minor axis is about 89% ± 3% of the major. Characteristic of other globulars, it has little of the elements other than hydrogen and helium; astronomers term this low metallicity. Specifically, relative to the Sun, its iron abundance is [Fe/H] = –2.32 dex, which is 0.5% of 1.0, on this logarithmic scale, the solar abundance. This puts the estimated age range for the cluster at 11 ± 1.5 billion years. Its true diameter is 108 ly, and may have a mass corresponding to 330,000 suns. The cluster is not yet in, nor guaranteed to undergo, core collapse and the core radius figures as about 2 arcseconds (″). It is an Oosterhoff type II (OoII) globular cluster, which means it belongs to the group of metal-poor clusters with longer period RR Lyrae variable stars. The 1997 Catalogue of Variable Stars in Globular Clusters listed 28 candidate variable stars in the cluster, although only 20 have been confirmed. As of 2001, there are 17 known RR Lyrae variables in Messier 92. 10 X-ray sources have been detected within the 1.02 arcminute half-mass radius of the cluster, of which half are candidate cataclysmic variable stars.

M92 is approaching us at 112 km/sec. Its coordinates indicate that the Earth's North Celestial Pole periodically passes less than one degree of this cluster during the precession of Earth's axis. Thus, M92 was a "Polarissima Borealis", or "North Cluster", about 12,000 years ago (10,000 BC), and it will again in about 14,000 years (16,000 AD). The multiple stellar populations in this cluster, revealing that it hosts at least two stellar generations of stars named 1G and 2G, as well as two distinct groups of 2G stars (2GA and 2GB). The helium abundances of 2GA and 2GB stars have higher mass fractions than that of the 1G stars by 0.01 and 0.04, respectively.

Gallery

Illustrations

Worked examples

Example 1 — a first encounter with Messier 92

Start with the simplest possible case. Write down what Messier 92 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 92 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 92 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 92

In research: Messier 92 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 92 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 92 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1777, Discoveries by Johann Elert Bode, Globular clusters, so understanding it makes those chapters shorter.
In everyday life: Look for Messier 92 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 92 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Messier 92 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 92 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Messier 92 in simple terms?

Messier 92 (also known as M92, M 92, or NGC 6341) is a globular cluster of stars in the northern constellation of Hercules. Discovery It was discovered by Johann Elert Bode on December 27, 1777, then published in the Berliner Astronomisches Jahrbuch during 1779.

Why does Messier 92 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 92?

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 92.