astronomy

NU Orionis

NU Orionis 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 NU Orionis rather than just read about it. In short: NU Orionis (HD 37061) is a quadruple star system in the Orion constellation. It is located in the emission nebula Messier 43 and is the main star ionizing it.

Key takeaways

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

Reference excerpt

NU Orionis (HD 37061) is a quadruple star system in the Orion constellation. It is located in the emission nebula Messier 43 and is the main star ionizing it. The distance to the system is 1,360 light-years (420 parsecs), as determined by its stellar parallax.

Location NU Orionis is within Messier 43 (M43), an emission nebula and H II region that is inside the Orion Nebula. It is the main star ionizing M43, with its radiation sculpting the nebula. Due to its faint apparent magnitude of 6.8, NU Orionis cannot be seen with the unaided eye, requiring at least binoculars to be seen. Messier 43 itself is magnitude 9, and can be seen with a small telescope. It culminates and is best seen in January.

NU Orionis was identified to be responsible for photoevaporation of several protoplanetary disks around stars in M43. These objects are also called proplyds. Two proplyds were discovered with the Hubble Space Telescope and later one additional proplyd was discovered with the James Webb Space Telescope.

Variability

NU Orionis is classified as "INSA" in the General Catalogue of Variable Stars. This acronym means that it is an Orion variable – a hot star with irregular variation – surrounded in nebulosity. The apparent magnitude varies from 6.80 to 6.93. Such classification is typical of hot, very young stars in the early stages of evolution. The estimated age of NU Ori is 3 million years.

Star system

NU Orionis was believed to be a single star until 1991, when spectroscopic observations revealed it to be a close binary with an orbital period of about 19 days. Subsequently, the distant companion HD 37061 B was discovered in 1999, at a distance of 470 milliarcseconds (mas). In 2013, a candidate fourth member named HD 37061 C was announced, discovered using interferometry at a distance of 15 mas from the central pair. It was confirmed in 2018. The primary component, NU Orionis Aa, is a B-type main-sequence star with 16.4 times the mass of the Sun and 5.7 times the radius of the Sun, radiating 27,000 times the solar luminosity. Its companion, NU Orionis Ab, orbits with a period of 14.3027 days and is separated by 0.36 astronomical units; the orbit is nearly circular. The star has 4.4 times the mass and 2.5 times the radius of the Sun, radiating 350 times the radiation the Sun does. The tertiary NU Orionis C is a B-type main-sequence star with 8.1 times the mass, 3.6 times the radius, and radiates 2,800 times the Sun's luminosity. The star has a strong magnetic field. It orbits the Aa-Ab pair with an orbital period of 476 days (1.30 years) and is separated by 3.77 au. The outer companion B is an A or B-main sequence star with 3.8 times the mass, 2.3 times the radius and 190 times the Sun's luminosity. It has a projected separation of 195 au to the inner triple, an orbit too large to currently have its elements measurable. The components Aa, B and C are rapid rotators, spinning with projected rotational velocities of 190, 180 and 104 km/s respectively. Component C's rotation period has been measured at around 1.09 days.

See also Trapezium Cluster Young stellar object Star formation

References

Illustrations

Worked examples

Example 1 — a first encounter with NU Orionis

Start with the simplest possible case. Write down what NU Orionis 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 NU Orionis 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 NU Orionis 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 NU Orionis

In research: NU Orionis 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 NU Orionis 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: NU Orionis is common in secondary-school and first-year university syllabi. It links to neighbouring topics A-type main-sequence stars, B-type main-sequence stars, Durchmusterung objects, so understanding it makes those chapters shorter.
In everyday life: Look for NU Orionis 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “NU Orionis” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study NU Orionis in 20 minutes

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

Frequently asked questions

What is NU Orionis in simple terms?

NU Orionis (HD 37061) is a quadruple star system in the Orion constellation. It is located in the emission nebula Messier 43 and is the main star ionizing it.

Why does NU Orionis 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 NU Orionis?

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 NU Orionis.