astronomy

S Orionis

S 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 S Orionis rather than just read about it. In short: S Orionis is an asymptotic giant branch star in the constellation Orion, approximately 480 parsecs (1,600 ly) away. It varies regularly in brightness between extremes of magnitude 7.2 and 14 every 14 months.

Key takeaways

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

Reference excerpt

S Orionis is an asymptotic giant branch star in the constellation Orion, approximately 480 parsecs (1,600 ly) away. It varies regularly in brightness between extremes of magnitude 7.2 and 14 every 14 months.

Variability

S Orionis is a Mira variable that pulsates with an approximately 420‑day cycle, and varies in radius from 2.0 to 2.3 astronomical units. The pulsations have been observed using VLTI and VLBA observations which measured an angular diameter varying between 7.9 and 9.7 mas. The mean period of variation has been shown to change over time, from less than 410 days to over 440 days. The variations are approximately sinusoidal with a weak, not statistically-significant, trend towards longer period. The cycle of period changes is around 70 years within a total observation period of only about 100 years, so it is difficult to be certain about long-term behaviour. However, this behaviour is not expected to be the result of thermal pulses or evolutionary changes, and the cause is unknown.

Companion S Orionis is listed in the Washington Double Star Catalog as a double star with a tenth magnitude companion 47" away. The companion is G0 star HD 294176.

Circumstellar environment S Orionis is surrounded by masers and dust condensed from its cool stellar wind. The size of the dust shells varies as the star pulsates and changes temperature, from around 8 AU to 10 AU across. The positions of the masers have been measured very accurately using VLBI.

References

Illustrations

Worked examples

Example 1 — a first encounter with S Orionis

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

In research: S 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 S 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: S Orionis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Durchmusterung objects, Emission-line stars, Henry Draper Catalogue objects, so understanding it makes those chapters shorter.
In everyday life: Look for S 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.

Affiliate

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

How to study S Orionis in 20 minutes

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

Frequently asked questions

What is S Orionis in simple terms?

Why does S 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 S 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 S Orionis.