astronomy

HD 12139

HD 12139 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 HD 12139 rather than just read about it. In short: HD 12139 is an orange-hued star in the northern zodiac constellation of Aries. With an apparent visual magnitude of 5.89, it is a dim star that is just visible to the naked eye under good viewing conditions.

Key takeaways

HD 12139 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect HD 12139 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 12139 from memory before moving on to harder problems.

Reference excerpt

HD 12139 is an orange-hued star in the northern zodiac constellation of Aries. With an apparent visual magnitude of 5.89, it is a dim star that is just visible to the naked eye under good viewing conditions. It is located approximately 348 light-years (106.6 pc) distant from the Sun, based on parallax, but is drifting closer with a radial velocity of −2 km/s. With high probability, it is considered a member of the Hercules stream. This object is an aging red giant with a stellar classification of K0III-IV, meaning that it has used up its core hydrogen and is expanding. At present it has 11 times the girth of the Sun. The star is about two billion years old with 1.7 times the mass of the Sun. It is radiating 58 times the luminosity of the Sun from its photosphere at an effective temperature of 4,780 K. A magnitude 9.36 companion is located at an angular separation of 199.70″ from the primary along a position angle of 9°, as of 2015. It is unclear if the two are physically associated.

References

Worked examples

Example 1 — a first encounter with HD 12139

Start with the simplest possible case. Write down what HD 12139 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 HD 12139 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 HD 12139 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 HD 12139

In research: HD 12139 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 HD 12139 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: HD 12139 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aries (constellation), Bright Star Catalogue objects, Double stars, so understanding it makes those chapters shorter.
In everyday life: Look for HD 12139 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 HD 12139 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 12139 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 HD 12139 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 12139 in simple terms?

Why does HD 12139 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 HD 12139?

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 HD 12139.