astronomy

Messier 108

Messier 108 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 108 rather than just read about it. In short: Messier 108 (also known as NGC 3556, nicknamed the Surfboard Galaxy) is a barred spiral galaxy about 46 million light-years away from Earth in the northern constellation Ursa Major. It was discovered by Pierre Méchain in 1781 or 1782.

Key takeaways

Messier 108 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 108 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Messier 108 from memory before moving on to harder problems.

Reference excerpt

Messier 108 (also known as NGC 3556, nicknamed the Surfboard Galaxy) is a barred spiral galaxy about 46 million light-years away from Earth in the northern constellation Ursa Major. It was discovered by Pierre Méchain in 1781 or 1782. From the Earth, this galaxy is seen almost edge-on. This galaxy is an isolated member of the Ursa Major Cloud of galaxies in the local supercluster. It has a morphological classification of type SBbc in the de Vaucouleurs system, which means it is a barred spiral galaxy with somewhat loosely wound arms. The maximum angular size of the galaxy in the optical band is 11′.1 × 4′.6, and it is inclined 75° to the line of sight. This galaxy has an estimated mass of 125 billion solar masses (M☉) and bears about 290 ± 80 globular clusters. Examination of the distribution of neutral hydrogen in this galaxy shows discrete shells of expanding gas extending for several kiloparsecs, known as H1 supershells. These may be driven by currents of dark matter, dust and gas contributing to large star formation, having caused supernovae explosions. Alternatively they may result from an infall from the intergalactic medium or arise from radio jets. Observations with the Chandra X-ray Observatory have identified 83 X-ray sources, including a source at the nucleus. The brightest of these is consistent with an intermediate-mass black hole accreting matter. The galaxy is also emitting a diffuse soft X-ray radiation within 2.6 arcminutes of the optical galaxy. The spectrum of the source at the core is consistent with an active galactic nucleus, but an examination with the Spitzer Space Telescope showed no indication of activity. The supermassive black hole at the core has an estimated mass of 24 million solar masses (M☉).

Supernovae Four supernovae have been observed in M108:

SN 1969B (type unknown, mag. 16) was discovered by Paul Wild on 6 February 1969, and independently by Balázs on 10 February 1969. It reached a brightness of mag. 13.9. SPIRITS 16tn was discovered by the Spitzer Space Telescope in August 2016. The supernova was only visible in infrared light, because it was heavily obscured by dust. Its extinction was estimated to be 8–9 mag, making it one of the most heavily obscured supernovae ever observed. SN 2023dbc (Type Ic, mag. 17) was discovered by the Zwicky Transient Facility on 13 March 2023. 2023dbc is likely a stripped-envelope supernova as there is no evidence for hydrogen in these spectra beyond narrow emission associated with the underlying HII region. It is among the nearest Type Ic supernovae discovered to date. SN 2025ahqr (Type Iax[02cx-like], mag. 20.0269) was discovered by the Zwicky Transient Facility on 23 November 2025. It is highly reddened, suggesting that it is strongly extincted by dust. At the time of discovery, it is the closest low luminosity Type Iax supernova known.

See also List of Messier objects NGC 2403 - a similar spiral galaxy NGC 4631 - a similar spiral galaxy NGC 7793 - a similar spiral galaxy

Notes

References

External links

SEDS: Spiral Galaxy M108

Messier 108 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

Illustrations

Worked examples

Example 1 — a first encounter with Messier 108

Start with the simplest possible case. Write down what Messier 108 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 108 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 108 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 108

In research: Messier 108 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 108 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 108 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1781, Barred spiral galaxies, Discoveries by Pierre Méchain, so understanding it makes those chapters shorter.
In everyday life: Look for Messier 108 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 108 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Messier 108 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 108 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Messier 108 in simple terms?

Why does Messier 108 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 108?

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 108.