astronomy

HD 91312

HD 91312 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 91312 rather than just read about it. In short: HD 91312 is a multiple star system in the northern circumpolar constellation Ursa Major. Faintly visible to the naked eye, it is the brightest star of Ursa Major without Flamsteed designation with a combined apparent visual magnitude of 4.72.

Key takeaways

HD 91312 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 91312 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 91312 from memory before moving on to harder problems.

Reference excerpt

HD 91312 is a multiple star system in the northern circumpolar constellation Ursa Major. Faintly visible to the naked eye, it is the brightest star of Ursa Major without Flamsteed designation with a combined apparent visual magnitude of 4.72. The system is located at a distance of 109 light-years from the Sun based on parallax. The radial velocity is poorly constrained, but it appears to be drifting further away at a rate of ~9 km/s. This was identified as a visual binary by John Herschel in 1831. The pair have an angular separation of 23″, equivalent to a linear projected separation of ~796 AU. Variations in the radial velocity as well as direct imaging, indicate the presence of a low-mass stellar companion. This companion is an early-to-mid red dwarf, and orbits the primary on an edge-on orbit with a semi-major axis of 9.7 au. This is a young system with an age of around 200 million years. It display an infrared excess from a circumstellar disk of dusty debris. It has a mean temperature of 35 K and is orbiting 218.1 AU from the inner pair. This star is relatively bright, but it was rarely included in old catalogues. Catalogues and atlases it was not included in are, for example, those by Ptolemy and all its derivatives and translations (by as-Sufi, al-Biruni, Ulugh Beg, Copernicus, Clavius, etc.), Tycho Brahe, de Houtman, Bayer, Kepler, Schiller, Halley, Flamsteed (as well as published by Carolina Herschel in 1798 catalogue of stars, observed by Flamsteed, but not inserted in his British Catalogue) and Bradley. Catalogues and atlases it was included in are those by Hevelius (1690) (65th in Ursa Major, designated In Ungula sinistri Pedis poster. trium sequens) and Bode (1801) (number 157 of Ursa Major). Bode used extended Bayer designations for some stars, and HD 91312 also was assigned designation "w", whereas original Bayer designations for Ursa Major stars are all Greek letters and Latin letters from "A" to "h".

References

Illustrations

Worked examples

Example 1 — a first encounter with HD 91312

Start with the simplest possible case. Write down what HD 91312 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 91312 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 91312 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 91312

In research: HD 91312 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 91312 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 91312 is common in secondary-school and first-year university syllabi. It links to neighbouring topics A-type subgiants, Bright Star Catalogue objects, Circumstellar disks, so understanding it makes those chapters shorter.
In everyday life: Look for HD 91312 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 91312 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 91312 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 91312 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 91312 in simple terms?

Why does HD 91312 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 91312?

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 91312.