astronomy

HD 101581

HD 101581 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 101581 rather than just read about it. In short: HD 101581 (TOI-6276, Gliese 435) is a nearby K-type main-sequence star located in the constellation Centaurus, approximately 41.7 light-years (12.8 parsecs) away, based on a parallax of 78.227 mas. At an apparent magnitude of 7.8, it is too faint to be seen with the naked eye, although it can be viewed with a small telescope.

Key takeaways

HD 101581 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 101581 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 101581 from memory before moving on to harder problems.

Reference excerpt

HD 101581 (TOI-6276, Gliese 435) is a nearby K-type main-sequence star located in the constellation Centaurus, approximately 41.7 light-years (12.8 parsecs) away, based on a parallax of 78.227 mas. At an apparent magnitude of 7.8, it is too faint to be seen with the naked eye, although it can be viewed with a small telescope. HD 101581 has a spectral type of K5V, which classifies it as a main sequence star (similar to the Sun) having the core hydrogen converted into helium. It has 0.65 times the Solar mass and 0.63 times the Solar radius while its age is estimated to be about 6.9 billion years old. Its surface has an effective temperature of 4633 K giving it the typical orange hue of a K-type star. The metallicity index of it is −0.344±0.059, indicating an iron-to-hydrogen ratio 45% that of the Sun.

Planetary system In 2024, two validated Earth-size planets orbiting HD 101581 were discovered via the transit method by TESS. These planets have orbital periods of 4.5 and 6.2 days, respectively. A candidate third small transiting planet in a wider orbit was possibly detected. The host star is the brightest star (in visual magnitude) with multiple known transiting Earth-size exoplanets, which should enable the atmospheric study of its orbiting planets via transmission spectroscopy in the near-future.

See also K2-138, which has a similar architecture "peas-in-pod" of planetary system LTT 1445, another nearby star system with transiting Earth-size planets Gliese 436

References

Worked examples

Example 1 — a first encounter with HD 101581

Start with the simplest possible case. Write down what HD 101581 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 101581 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 101581 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 101581

In research: HD 101581 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 101581 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 101581 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Centaurus, Durchmusterung objects, Gliese and GJ objects, so understanding it makes those chapters shorter.
In everyday life: Look for HD 101581 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 101581 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 101581 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 101581 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 101581 in simple terms?

Why does HD 101581 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 101581?

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 101581.