astronomy

HD 156846

HD 156846 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 156846 rather than just read about it. In short: HD 156846 is a binary star system in the equatorial constellation of Ophiuchus, positioned a degree SSE of Messier 9. It has a yellow hue and is just barely bright enough to be visible to the naked eye with an apparent visual magnitude of 6.5.

Key takeaways

HD 156846 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 156846 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 156846 from memory before moving on to harder problems.

Reference excerpt

HD 156846 is a binary star system in the equatorial constellation of Ophiuchus, positioned a degree SSE of Messier 9. It has a yellow hue and is just barely bright enough to be visible to the naked eye with an apparent visual magnitude of 6.5. The system is located at a distance of 156 light years from the Sun based on parallax. It is drifting closer with a radial velocity of −68.5 km/s, and is predicted to come to within 85.0 light-years in about 476,000 years. The primary, component A, is a G-type star with a stellar classification of G1V. The absolute visual magnitude of this star is 1.13 magnitudes above the main sequence, indicating it has evolved slightly off the main sequence. It has 1.35 times the mass of the Sun and 2.12 times the Sun's radius. The star is an estimated 2.8 billion years old and is spinning with a projected rotational velocity of 5 km/s. It is radiating five times the luminosity of the Sun from its photosphere at an effective temperature of 5,969 K. The magnitude 14.1 secondary companion, component B, was discovered by the American astronomer R. G. Aitken in 1910. It lies at an angular separation of 5.1″ from the primary, corresponding to a projected separation of 250 AU. This is a red dwarf with a class of M4V and has an estimated 59% of the Sun's mass.

Planetary system On 26 October 2007, a planet HD 156846 b was found orbiting the primary star by Tamuz, using the radial velocity method. It has an orbital period of 0.98 years and a large eccentricity of 0.85. The estimated mass of this object is, at a minimum, 10.6 times the mass of Jupiter. If it were following the same orbit within the Solar System, it would have a perihelion within the orbit of Mercury and an aphelion outside the orbit of Mars.

See also HD 4113 List of extrasolar planets

References

Worked examples

Example 1 — a first encounter with HD 156846

Start with the simplest possible case. Write down what HD 156846 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 156846 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 156846 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 156846

In research: HD 156846 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 156846 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 156846 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Binary stars, Bright Star Catalogue objects, Durchmusterung objects, so understanding it makes those chapters shorter.
In everyday life: Look for HD 156846 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 156846 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 156846 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 156846 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 156846 in simple terms?

Why does HD 156846 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 156846?

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 156846.