astronomy

Messier 61

Messier 61 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 61 rather than just read about it. In short: Messier 61 (also known as M61, NGC 4303, or the Swelling Spiral Galaxy) is an intermediate barred spiral galaxy in the Virgo Cluster of galaxies. It was first discovered by Barnaba Oriani on May 5, 1779, six days before Charles Messier discovered the same galaxy.

Key takeaways

Messier 61 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 61 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Messier 61 from memory before moving on to harder problems.

Reference excerpt

Messier 61 (also known as M61, NGC 4303, or the Swelling Spiral Galaxy) is an intermediate barred spiral galaxy in the Virgo Cluster of galaxies. It was first discovered by Barnaba Oriani on May 5, 1779, six days before Charles Messier discovered the same galaxy. Messier had observed it on the same night as Oriani but had mistaken it for a comet. Its distance has been estimated to be 45.61 million light years from the Milky Way Galaxy. It is a member of the M61 Group of galaxies, which is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster.

Properties M61 is one of the largest members of Virgo Cluster, and belongs to a smaller subgroup known as the S Cloud. The morphological classification of SAB(rs)bc indicates a weakly-barred spiral (SAB) with the suggestion of a ring structure (rs) and moderate to loosely wound spiral arms. It has an active galactic nucleus and is classified as a starburst galaxy containing a massive nuclear star cluster with an estimated mass of 1 million solar masses (M☉) and an age of 4 million years, as well as a central candidate supermassive black hole weighing around 5 million M☉. It cohabits with an older massive star cluster as well as a likely older starburst. Evidence of significant star formation and active bright nebulae appears across M61's disk. Unlike most late-type spiral galaxies within the Virgo Cluster, M61 shows an unusual abundance of neutral hydrogen (H I). In 2026, a stellar stream was discovered north of Messier 61 using the Vera C. Rubin Observatory.

Supernovae Eight supernovae have been observed in M61, making it one of the most prodigious galaxies for such cataclysmic events. These include:

SN 1926A (Type II, mag. 14) was discovered by Max Wolf and Karl Wilhelm Reinmuth on 9 May 1926. SN 1961I (Type II, mag. 13) was discovered by Milton Humason on 3 June 1961. SN 1964F (Type II, mag. 14) was discovered by Leonida Rosino on 30 June 1964. SN 1999gn (Type II, mag. 16) was discovered by Alessandro Dimai on 17 December 1999. SN 2006ov (Type II, mag. 14.9) was discovered by Kōichi Itagaki on 24 November 2006. SN 2008in (Type II, mag. 14.9) was discovered by Kōichi Itagaki on 26 December 2008. SN 2014dt (Type Ia-pec, mag. 13.6) was discovered by Kōichi Itagaki on 29 October 2014. SN 2020jfo (Type II, mag. 16.01) was discovered by the Zwicky Transient Facility on 6 May 2020.

Gallery

Illustrations

Worked examples

Example 1 — a first encounter with Messier 61

Start with the simplest possible case. Write down what Messier 61 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 61 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 61 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 61

In research: Messier 61 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 61 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 61 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1779, IRAS catalogue objects, Intermediate spiral galaxies, so understanding it makes those chapters shorter.
In everyday life: Look for Messier 61 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 61 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Messier 61 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 61 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Messier 61 in simple terms?

Why does Messier 61 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 61?

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 61.