astronomy

Messier 66

Messier 66 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 66 rather than just read about it. In short: Messier 66 or M66, also known as NGC 3627, is an intermediate spiral galaxy located around 31 million light years from Earth in the equatorial half of the Leo constellation. This galaxy is a member of the Leo Triplet (M66 group), a small group of galaxies that includes M65 and NGC 3628.

Key takeaways

Messier 66 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 66 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Messier 66 from memory before moving on to harder problems.

Reference excerpt

Messier 66 or M66, also known as NGC 3627, is an intermediate spiral galaxy located around 31 million light years from Earth in the equatorial half of the Leo constellation. This galaxy is a member of the Leo Triplet (M66 group), a small group of galaxies that includes M65 and NGC 3628. M66 has a morphological classification of SABb, indicating that is has a spiral shape with a weak bar feature and loosely wound arms. It was discovered by French astronomer Charles Messier on 1 March 1780, who described it as "very long and very faint". Messier 65 and Messier 66 are a common object for amateur astronomic observation, being separated by only 20′.

Characteristics Messier 66 is an intermediate spiral galaxy. It has a weak bar and a loosely wounded spiral structure. It is about 95 thousand light-years across. The galaxy has striking dust lanes and bright star clusters along its spiral arms. It also has a well-developed central bulge. The isophotal axis ratio is 0.32, indicating that it is being viewed at an angle. The galaxy has a high rate of star formation occurring in the spiral arms. Its rate of star formation is about 0.05 solar masses per year. These young stars ionize their surrounding environment.

Interaction Gravitational interaction from its past encounter with neighboring NGC 3628 has resulted in an extremely high central mass concentration and a high molecular to atomic mass ratio. This also resulted in a resolved non-rotating clump of H I material apparently removed from one of the spiral arms. The latter feature shows up visually as an extremely prominent and unusual spiral arm and dust lane structures as originally noted in the Atlas of Peculiar Galaxies.

Supernovae Five supernovae have been observed in M66:

SN 1973R (Type II, mag. 14.5) was discovered by Leonida Rosino on 19 December 1973. SN 1989B (Type Ia, mag. 13) was discovered by Robert Evans on 30 January 1989. SN 1997bs (type uncertain, mag. 17) was discovered by the Lick Observatory Supernova Search (LOSS) on 15 April 1997. This event was initially classified as a Type IIn supernova, but later analysis suggests that it is instead either a luminous blue variable, a "gap" transient, or a luminous red nova. SN 2009hd (Type II, mag. 15.8) was discovered by Berto Monard on 2 July 2009. SN 2016cok (Type II-P, mag. 16.6) was discovered by the All Sky Automated Survey for Supernovae on 28 May 2016.

Gallery

Illustrations

Worked examples

Example 1 — a first encounter with Messier 66

Start with the simplest possible case. Write down what Messier 66 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 66 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 66 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 66

In research: Messier 66 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 66 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 66 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Arp objects, Astronomical objects discovered in 1780, Discoveries by Charles Messier, so understanding it makes those chapters shorter.
In everyday life: Look for Messier 66 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 66 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Messier 66 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 66 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Messier 66 in simple terms?

Why does Messier 66 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 66?

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 66.