astronomy

HD 138867

HD 138867 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 138867 rather than just read about it. In short: HD 138867, also known as HR 5786, is a bluish-white hued star located in the southern circumpolar constellation Apus. It has an apparent magnitude of 5.94, making it faintly visible to the naked eye if viewed under ideal conditions.

Key takeaways

HD 138867 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 138867 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 138867 from memory before moving on to harder problems.

Reference excerpt

HD 138867, also known as HR 5786, is a bluish-white hued star located in the southern circumpolar constellation Apus. It has an apparent magnitude of 5.94, making it faintly visible to the naked eye if viewed under ideal conditions. Based on parallax measurements from the Gaia spacecraft, it is estimated to be 417 light years away from Earth. However, it is receding with a heliocentric radial velocity of 1.1 km/s. HD 138867 has a stellar classification of B9.5 V, indicating that it is a B-type main-sequence star just shy of being an A-type star. It has 2.81 times the mass of the Sun and is estimated to be 272 million years, having completed 67.4% of its main sequence lifetime. HD 138867 has an effective temperature of 10,375 K, which combined with a radius of 2.59 R☉, yields a luminosity over 50 times that of Sun. A solar metallicity has been calculated for HD 138867. It is currently spinning rapidly with a projected rotational velocity of 178 km/s. There has been disagreement in regards to HD 138867's muplicity. Chini et al. (2012) list it as a solitary star while Eggleton and Tokovinn (2008) found it to be an astrometric binary. The first one is more likely as the object has a constant radial velocity.

References

Worked examples

Example 1 — a first encounter with HD 138867

Start with the simplest possible case. Write down what HD 138867 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 138867 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 138867 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 138867

In research: HD 138867 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 138867 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 138867 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Apus, B-type main-sequence stars, Bright Star Catalogue objects, so understanding it makes those chapters shorter.
In everyday life: Look for HD 138867 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 138867 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 138867 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 138867 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 138867 in simple terms?

Why does HD 138867 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 138867?

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 138867.