astronomy

NGC 4902

NGC 4902 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 NGC 4902 rather than just read about it. In short: NGC 4902 is a barred spiral galaxy in the constellation Virgo. The galaxy lies about 110 million light years away from Earth, which means, given its apparent dimensions, that NGC 4902 is approximately 100,000 light years across.

Key takeaways

NGC 4902 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect NGC 4902 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 4902 from memory before moving on to harder problems.

Reference excerpt

NGC 4902 is a barred spiral galaxy in the constellation Virgo. The galaxy lies about 110 million light years away from Earth, which means, given its apparent dimensions, that NGC 4902 is approximately 100,000 light years across. It was discovered by German-British astronomer William Herschel on February 8, 1785.

Characteristics NGC 4902 has a prominent bar. There is a brighter stellar feature visible on the southwest side of the bar, but it could also be superimposed. Two spiral arms emerge at the ends of the bar and overlap, forming an inner ring. There is a kink at the north side of the ring. Three spiral arms emanate from the ring, along with a fainter arm. The third arm appears semi-detacted from the inner ring. The arms are diffuse and feature many HII regions. The star formation rate of the galaxy is estimated to be 3.8 M☉ per year.

Supernovae Three supernovae have been observed in NGC 4902:

SN 1979E (type unknown) was discovered on a photographic plate exposed on 19 August 1979 by M. Wischnjewsky at an apparent magnitude of 16. SN 1991X was discovered by Robert Evans on 5 May 1991 at an estimated apparent magnitude of 13.5–14. It was located on the edge of the bar, near the inner ring. It was identified spectrographically as a Type Ia supernova near maximum light. SN 2011A was discovered on 4 January 2011 by the CHASE project using the 0.41-m 'PROMPT 4' telescope at Cerro Tololo Inter-American Observatory at an apparent magnitude of 16.9. It was initially classified spectrographically as a Type IIn supernova, however due to its low luminosity and low ejecta velocity has been suggested to be a supernova impostor.

Nearby galaxies NGC 4902 is the foremost galaxy of a galaxy group known as the NGC 4902 Group. Other members of the group include NGC 4887, NGC 4897, and NGC 4899. NGC 4899 lies 34 arcminutes north of NGC 4902 and NGC 4897 64 arcminutes north. The size of the group is similar to that of the Local Group. It belongs at the same galaxy cloud as NGC 5054, and is part of the Virgo Supercluster, located with in the Virgo II Groups or Virgo Southern Extension.

References

External links NGC 4902 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images NGC 4902 on SIMBAD

Illustrations

Worked examples

Example 1 — a first encounter with NGC 4902

Start with the simplest possible case. Write down what NGC 4902 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 NGC 4902 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 NGC 4902 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 NGC 4902

In research: NGC 4902 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 NGC 4902 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: NGC 4902 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1785, Barred spiral galaxies, Discoveries by William Herschel, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 4902 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 NGC 4902 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 4902 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 NGC 4902 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 4902 in simple terms?

Why does NGC 4902 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 NGC 4902?

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 NGC 4902.