astronomy

HD 139357 b

HD 139357 b 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 b rather than just read about it. In short: HD 139357 b is a very massive extrasolar planet or brown dwarf located approximately 390 light years away, orbiting the 6th magnitude K-type giant star HD 139357 in the constellation of Draco. The detection occurred on March 20, 2009, which was the first day of spring.

Key takeaways

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

Reference excerpt

HD 139357 b is a very massive extrasolar planet or brown dwarf located approximately 390 light years away, orbiting the 6th magnitude K-type giant star HD 139357 in the constellation of Draco. The detection occurred on March 20, 2009, which was the first day of spring. The actual mass and radius of this body remain uncertain, but it has a minimum mass of nearly 10 times that of Jupiter and a radius of probably no more than 1.2 times Jupiter's. Most likely this is a brown dwarf rather than a planet. The reason why the object's true mass was initially unknown is due to the undetermined inclination of its orbital plane. Follow up observations via direct imaging may determine its radius and orbital inclination, thereby giving its density and surface gravity, which will allow a determination as to whether this object is a brown dwarf or a supermassive planet. 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. As it is typical for supermassive planets, this orbits further from its host star than Earth is from the Sun. The planet's year is over three Earth years. However, the orbital eccentricity of this object is much greater than Earth's: 0.1 vs. 0.017. Like most known extrasolar planets, it was detected by the wobble method, which detects planets through the circular wobbling motion of the star caused by the gravity of orbiting body.

Worked examples

Example 1 — a first encounter with HD 139357 b

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

In research: HD 139357 b 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 b 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 b is common in secondary-school and first-year university syllabi. It links to neighbouring topics Draco (constellation), Exoplanets detected by astrometry, Exoplanets detected by radial velocity, so understanding it makes those chapters shorter.
In everyday life: Look for HD 139357 b 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 b in 20 minutes

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

Frequently asked questions

What is HD 139357 b in simple terms?

Why does HD 139357 b 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 b?

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 b.