astronomy

NGC 2403

NGC 2403 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 2403 rather than just read about it. In short: NGC 2403 is an intermediate spiral galaxy in the constellation Camelopardalis. Alternatively, it is known as Caldwell 7.

Key takeaways

NGC 2403 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 2403 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 2403 from memory before moving on to harder problems.

Reference excerpt

NGC 2403 is an intermediate spiral galaxy in the constellation Camelopardalis. Alternatively, it is known as Caldwell 7. It is an outlying member of the M81 Group of galaxies, and is approximately 9.7 million light-years distant.

Observation history The galaxy was discovered by German-British astronomer William Herschel on 1 November 1788. Edwin Hubble detected Cepheid variables in NGC 2403 using the Hale Telescope, making it the first galaxy beyond the Local Group within which a Cepheid was discovered. By 1963, 59 variables had been found in NGC 2403, of which 17 were eventually confirmed as Cepheids, with periods between 20 and 87 days. As late as 1950 Hubble was using a distance of just under 2 million light years for the galaxy's distance, but by 1968 the analysis of the Cepheids increased this by almost a factor of five, to within 0.2 magnitudes of the current value.

Characteristics

NGC 2403 bears a similarity to M33, containing numerous star-forming H II regions, but being a little bit larger at approximately 90,000 light-years in diameter compared to the 61,100 light-year diameter of M33. It is a flocculent spiral galaxy, with short, patchy arms. The northern spiral arm connects it to the star forming region NGC 2404. NGC 2403 can be observed using 10×50 binoculars. NGC 2404 is 940 light-years in diameter, making it one of the largest known H II regions. This H II region represents striking similarity with NGC 604 in M33, both in size and location in galaxy.

Supernovae and supernovae imposters There have been four reported astronomical transients in the galaxy:

SN 1954J was first noticed by Gustav Tammann and Allan Sandage as a "bright blue irregular variable" star, which they named V12. They noted it underwent a major outburst on 2/3 November 1954, which attained a magnitude of 16 at its brightest. In 1972, Fritz Zwicky classified this event as a Type V supernova. It was later determined to be a supernova imposter: a highly luminous, very massive eruptive star, surrounded by a dusty nebula, similar to the 1843 Great Eruption of η Carinae in the Milky Way. SN 2002kg was discovered by LOTOSS (Lick Observatory and Tenagra Observatory Supernova Searches) on 26 October 2002 and initially classified as a Type IIn, or possibly the outburst of a luminous blue variable. On 24 August 2021, it was reclassified as a Gap transient. SN 2004dj (Type II-P, mag. 11.2) was discovered by Kōichi Itagaki on 31 July 2004. At the time of its discovery, it was the nearest and brightest supernova observed in the 21st century, and is now listed as the brightest supernova of 2004. AT 2016ccd, initially designated as SNhunt225, is a luminous blue variable, first discovered by Catalina Real-time Transient Survey (CRTS) and Stan Howerton in December 2013. Outbursts from this star have been observed as recently as November 2021.

Companions NGC 2403 has two known companions. One is the relatively massive dwarf galaxy DDO 44. It is currently being disrupted by NGC 2403, as evidenced by a tidal stream extending 82 kly (25 kpc) on both sides of DDO 44. DDO 44 is approaching NGC 2403 at a distance much closer than typical for dwarf galaxy interactions. It currently has a V-band absolute magnitude of −12.9, but its progenitor was even more luminous. The other known companion is officially named MADCASH J074238+652501-dw, although it is nicknamed MADCASH-1. The name refers to the MADCASH (Magellanic Analog Dwarf Companions and Stellar Halos) project. MADCASH-1 is similar to typical dwarf spheroidal galaxies in the Local Group; it is quite faint, with an absolute V-band magnitude of −7.81, and has only an ancient, metal-poor population of red giant stars.

See also Triangulum Galaxy – looks very similar to NGC 2403. List of NGC objects (2001–3000)

References

External links

Spiral Galaxy NGC 2403 at the astro-photography site of Mr. Takayuki Yoshida NGC 2403 at ESA/Hubble

NGC 2403 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images NASA Astronomy Picture of the Day: NGC 2403 (19 February 2016) SEDS – NGC 2403

Illustrations

Worked examples

Example 1 — a first encounter with NGC 2403

Start with the simplest possible case. Write down what NGC 2403 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 2403 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 2403 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 2403

In research: NGC 2403 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 2403 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 2403 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1788, Caldwell objects, Camelopardalis, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 2403 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 2403 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 2403 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 2403 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 2403 in simple terms?

NGC 2403 is an intermediate spiral galaxy in the constellation Camelopardalis. Alternatively, it is known as Caldwell 7.

Why does NGC 2403 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 2403?

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 2403.