astronomy

Messier 100

Messier 100 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 100 rather than just read about it. In short: Messier 100 (also known as NGC 4321 or the Mirror Galaxy) is a grand design intermediate spiral galaxy in the constellation of Coma Berenices. It is one of the brightest and largest galaxies in the Virgo Cluster and is approximately 55 million light-years from the Milky Way, about 166,000 light-years in diameter.

Key takeaways

Messier 100 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 100 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Messier 100 from memory before moving on to harder problems.

Reference excerpt

Messier 100 (also known as NGC 4321 or the Mirror Galaxy) is a grand design intermediate spiral galaxy in the constellation of Coma Berenices. It is one of the brightest and largest galaxies in the Virgo Cluster and is approximately 55 million light-years from the Milky Way, about 166,000 light-years in diameter. It was discovered by Pierre Méchain in 1781 and 29 days later seen again and entered by Charles Messier in his catalogue "of nebulae and star clusters". It was one of the first spiral galaxies to be discovered, and was listed as one of fourteen spiral nebulae by Lord William Parsons of Rosse in 1850. NGC 4323 and NGC 4328 are satellite galaxies of M100; the former is connected with it by a bridge of luminous matter.

Early observations

After the discovery of M100 by Méchain, Charles Messier made observations of the galaxy depicting it as a nebula without a star. He pointed out that it was difficult to recognize the nebula because of its faintness. William Herschel was able to identify a bright cluster of stars within the "nebula" during his observations. His son John expanded the findings in 1833. With the advent of better telescopes, John Herschel was able to see a round, brighter galaxy; however, he also mentioned that it was barely visible through clouds. William Henry Smyth extended the studies of M100, detailing it as a pearly white nebula and pointing out diffuse spots.

Star formation Messier 100 is considered a starburst galaxy with the strongest star formation activity concentrated in its center, within a ring – actually two tightly wound spiral arms attached to a small nuclear bar of radius: one thousand parsecs – where star formation has been taking place for at least 500 million years in separate bursts.

Supernovae

Seven supernovae have been identified in M100:

On 17 March 1901 Heber Curtis discovered SN 1901B (Type I, mag. 15.6), at 110"W and 4"N from the galaxy's nucleus. Heber Curtis discovered SN 1914A (type unknown, mag. 15.7) on 2 March 1914, at 24"E and 111"S from the galaxy's nucleus. Milton Humason, with observations from early to mid 1960, discovered SN 1959E (Type I, mag. 17.5), located 58"E and 21"S from the galaxy's nucleus. On 15 April 1979, amateur astronomer Gus Johnson discovered SN 1979C, the first Type II supernova found in the M100 galaxy. However, the star faded quickly, and later observations from x-ray to radio wavelengths revealed its remnant. SN 2006X (Type Ia, mag. 15.3) was discovered by Shoji Suzuki and Marco Migliardi on 7 February 2006, two weeks before fading to magnitude 17. Jaroslaw Grzegorzek discovered SN 2019ehk (Type Ib, mag. 16.5) on 29 April 2019. The supernova reached a peak magnitude of approximately 15.8. SN 2020oi (Type Ic, mag. 17.28) was discovered by Automatic Learning for the Rapid Classification of Events (ALeRCE) on 7 January 2020.

Illustrations

Worked examples

Example 1 — a first encounter with Messier 100

Start with the simplest possible case. Write down what Messier 100 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 100 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 100 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 100

In research: Messier 100 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 100 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 100 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1781, Coma Berenices, Discoveries by Pierre Méchain, so understanding it makes those chapters shorter.
In everyday life: Look for Messier 100 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 100 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Messier 100 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 100 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Messier 100 in simple terms?

Why does Messier 100 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 100?

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 100.