astronomy

Messier 37

Messier 37 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 37 rather than just read about it. In short: Messier 37 (also known as M37, NGC 2099, or the Salt and Pepper Cluster) is the brightest and richest open cluster in the constellation Auriga. It was discovered by the Italian astronomer Giovanni Battista Hodierna before 1654.

Key takeaways

Messier 37 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 37 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Messier 37 from memory before moving on to harder problems.

Reference excerpt

Messier 37 (also known as M37, NGC 2099, or the Salt and Pepper Cluster) is the brightest and richest open cluster in the constellation Auriga. It was discovered by the Italian astronomer Giovanni Battista Hodierna before 1654. M37 was missed by French astronomer Guillaume Le Gentil when he rediscovered M36 and M38 in 1749. French astronomer Charles Messier independently rediscovered M37 in September 1764 but all three of these clusters were recorded by Hodierna. It is classified as Trumpler type I,1,r or I,2,r. M37 exists in the antipodal direction, opposite from the Galactic Center as seen from Earth, so is in one of the nearby outer arms. Specifically it is still close enough to be in our own. Estimates of its age range from 347 million to 550 million years. It has 1,500 times the mass of the Sun (M☉) and contains over 500 identified stars, with roughly 150 stars brighter than magnitude 12.5. M37 has at least a dozen red giants and its hottest surviving main sequence star is of stellar classification B9 V. The abundance of elements other than hydrogen and helium, what astronomers term metallicity, is similar to, if not slightly higher than, the abundance in the Sun. As of 2022, it contains only the third known planetary nebula associated with an open cluster. At its estimated distance of around 4,500 light-years (1,400 parsecs) from Earth, the cluster's angular diameter of 24 arcminutes corresponds to a physical extent of about 20–25 ly (6.1–7.7 pc). The tidal radius of the cluster, where external gravitational perturbations begin to have a significant influence on the orbits of its member stars, is about 46–59 ly (14–18 pc). This cluster is following an orbit through the Milky Way with a period of 219.3 Ma and an eccentricity of 0.22. This will bring it as close as 19.6 kly (6.0 kpc) to, and as distant as 30.7 kly (9.4 kpc) from, the Galactic Center. It reaches a peak distance above the galactic plane of 0.29 kly (0.089 kpc) and will cross the plane with a period of 31.7 Ma.

Sky charts

Illustrations

Worked examples

Example 1 — a first encounter with Messier 37

Start with the simplest possible case. Write down what Messier 37 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 37 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 37 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 37

In research: Messier 37 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 37 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 37 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1654, Auriga, Messier objects, so understanding it makes those chapters shorter.
In everyday life: Look for Messier 37 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 37 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Messier 37 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 37 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Messier 37 in simple terms?

Why does Messier 37 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 37?

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 37.