astronomy

HD 82943

HD 82943 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 82943 rather than just read about it. In short: HD 82943 (164 G. Hydrae) is a star with a pair of orbiting exoplanets in the equatorial constellation of Hydra.

Key takeaways

HD 82943 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 82943 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 82943 from memory before moving on to harder problems.

Reference excerpt

HD 82943 (164 G. Hydrae) is a star with a pair of orbiting exoplanets in the equatorial constellation of Hydra. It has an apparent visual magnitude of 6.54, which is near the lower limit of visibility to the naked eye. Based on parallax measurements, the distance to this system is 90.3 light-years. It is drifting further away with a heliocentric radial velocity of 8.1 km/s. The star shows a high proper motion, traversing the celestial sphere at an angular rate of 0.194 arcsec yr−1. The spectrum of HD 82943 presents as an F-type main-sequence star with a stellar classification of F9 V Fe+0.5. The suffix notation indicates a mild strengthening of iron lines relative to a typical star of its type. Nonetheless, it is considered a metal-rich star, having a higher abundance of many elements with masses greater than helium as compared to the Sun. This star is around 3 billion years old and is spinning with a rotation period of 18 days. It is 14% more massive and has a 17% larger radius than the Sun. The star is radiating 154% of the luminosity of the Sun from its photosphere at an effective temperature of 5,944 K.

Planetary system The first exoplanet discovered (designated HD 82943 b) was announced in 2000 by a team of French astronomers led by Michel Mayor. The exoplanet orbits its parent star at a mean distance of 1.19 astronomical units (AU) and taking approximately 441 days to complete the orbit. Nearly a year later, a second exoplanet (designated HD 82943 c) was announced by the same discoverers of the previous planet. This exoplanet orbits closer than the other, at a mean distance of 0.746 AU and taking 219 days to complete its orbit. The two known exoplanet appear to have a 2:1 resonance with one another. Further radial velocity analysis hinted at either long-period stellar activity or presence of a third Jovian exoplanet with an orbital period of 1,075 days. Announced in 2001, HD 82943 was found to contain an unusually high abundance of lithium-6. Upon reaching a sufficient core temperature, young stars quickly burn through their initial allotment of lithium-6, whereas planets should retain their lithium-6. Thus the simplest and most convincing answer to explain this observation is that one or more planets, or at least planetary material, have fallen into the star sometime after it passed through its early evolutionary stage. A circumstellar debris disk was discovered in 2003, based on an infrared excess detected in the system. The inner edge of this disk orbits at a distance of 67 AU from the host star. The distance to the outer edge is poorly constrained.

Worked examples

Example 1 — a first encounter with HD 82943

Start with the simplest possible case. Write down what HD 82943 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 82943 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 82943 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 82943

In research: HD 82943 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 82943 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 82943 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Circumstellar disks, Durchmusterung objects, F-type main-sequence stars, so understanding it makes those chapters shorter.
In everyday life: Look for HD 82943 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 82943 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 82943 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 82943 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 82943 in simple terms?

HD 82943 (164 G. Hydrae) is a star with a pair of orbiting exoplanets in the equatorial constellation of Hydra.

Why does HD 82943 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 82943?

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 82943.