astronomy

HD 102365

HD 102365 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 102365 rather than just read about it. In short: HD 102365 (66 G. Centauri) is a binary star system that is located in the northeastern part of the Centaurus constellation, at a distance of about 30.4 light-years (9.3 parsecs) from the Solar System.

Key takeaways

HD 102365 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 102365 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 102365 from memory before moving on to harder problems.

Reference excerpt

HD 102365 (66 G. Centauri) is a binary star system that is located in the northeastern part of the Centaurus constellation, at a distance of about 30.4 light-years (9.3 parsecs) from the Solar System. The larger member of the system is a G-type star that is smaller than the Sun but of similar mass. It has a common proper motion companion that was discovered by W. J. Luyten in 1960. This M-type star appears to be in a wide orbit around the primary at a current separation of about 211 astronomical units (AU), (or 211 times the separation of the Earth from the Sun). By comparison, Neptune orbits at an average distance of 30 AU.

Description The stellar classification for the primary star in this system is G2V; the same as the Sun. That of the red dwarf companion is M4V. The primary star has an estimated 84% the mass of the Sun, 99% of the Sun's radius, and 86% of the Sun's luminosity. It is a slow rotator, with a projected rotational velocity of 0.5 km/s. The system is believed to be ancient, with modern estimates of the age between 11.0 and 13.1 billion years, over double that of the Solar System. Compared to the Sun, it only has about 52% of the abundance of elements other than hydrogen and helium; what astronomers term the metallicity of a star. This star system has a relatively large proper motion. The HR 4523 system is presently located within the Epsilon Indi Moving Group, although it gives itself away as an interloper, since the star is older and has a different composition than the group members. It has space velocity components [U, V, W] = [−67, −40, +4] km/s.

Search for planets The primary star has been believed to be orbited by a Neptune-like planet with a minimum mass 9.3 times that of the Earth. The orbital period of this planet is 122.1 days. No other planets have been discovered orbiting this star. Initially detected in 2012 by Doppler spectroscopy (radial velocity method), a 2013 study was unable to confirm this planet, but it was detected again in a 2023 study. Evidence suggested the radial velocity variations are indeed caused from the orbital motion of a planet, and not from intrinsic processes arising from the star. However, it was again undetected in ESPRESSO observations taken by a 2025 study, which found evidence that the radial velocity variations instead arise from the star's magnetic field. Similarly, another 2025 paper also reported a non-detection. The NASA Exoplanet Archive demoted the planet to false positive status in April 2026. An examination of this system in the infrared did not reveal an excess emission that would otherwise suggest the presence of a circumstellar debris disk.

References

External links HR 4523 AB, SolStation, archived from the original on April 25, 2001, retrieved 2011-10-11

Illustrations

Worked examples

Example 1 — a first encounter with HD 102365

Start with the simplest possible case. Write down what HD 102365 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 102365 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 102365 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 102365

In research: HD 102365 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 102365 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 102365 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Binary stars, Bright Star Catalogue objects, Centaurus, so understanding it makes those chapters shorter.
In everyday life: Look for HD 102365 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “HD 102365” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study HD 102365 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 102365 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 102365 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 102365 in simple terms?

Why does HD 102365 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 102365?

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 102365.