astronomy

HD 139357

HD 139357 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 139357 rather than just read about it. In short: HD 139357 is a 6th magnitude K-type giant star located approximately 370 light years from Earth, visible in the constellation Draco. Its mass is four thirds that of the Sun but its radius is 11.47 times larger.

Key takeaways

HD 139357 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 139357 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 139357 from memory before moving on to harder problems.

Reference excerpt

HD 139357 is a 6th magnitude K-type giant star located approximately 370 light years from Earth, visible in the constellation Draco. Its mass is four thirds that of the Sun but its radius is 11.47 times larger. However, despite being a giant star, it is only 3.07 billion years old, which is younger than the Sun. It hosts a substellar companion with a minimum mass of 9.76 MJ, discovered in 2009. A 2022 study estimated the true mass of HD 139357 b at about 16.38 MJ via astrometry, although this estimate is poorly constrained. If this is the true mass, the object would be a brown dwarf.

See also 42 Draconis Iota Draconis List of extrasolar planets

References

Worked examples

Example 1 — a first encounter with HD 139357

Start with the simplest possible case. Write down what HD 139357 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 139357 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 139357 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 139357

In research: HD 139357 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 139357 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 139357 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bright Star Catalogue objects, Draco (constellation), Durchmusterung objects, so understanding it makes those chapters shorter.
In everyday life: Look for HD 139357 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 139357 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 139357 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 139357 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 139357 in simple terms?

Why does HD 139357 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 139357?

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 139357.