astronomy

HD 117618

HD 117618 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 117618 rather than just read about it. In short: HD 117618, named Dofida by the IAU, is a single, yellow-hued star in the southern constellation of Centaurus. With an apparent visual magnitude of 7.17, it is too faint to be visible to the naked eyes of a typical observer.

Key takeaways

HD 117618 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 117618 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 117618 from memory before moving on to harder problems.

Reference excerpt

HD 117618, named Dofida by the IAU, is a single, yellow-hued star in the southern constellation of Centaurus. With an apparent visual magnitude of 7.17, it is too faint to be visible to the naked eyes of a typical observer. The distance to this star, as determined from its annual parallax shift of 26.54 mas as seen from Earth's orbit, is 123 light years. It is moving further away with a heliocentric radial velocity of around +1.6 km/s. This star is similar to the Sun, being a G-type main-sequence star with a stellar classification of G0 V. It is about 10% more massive and 17% larger than the Sun, with an estimated age of roughly four billion years and a projected rotational velocity of 3.67 km/s. The star is radiating 1.6 times the Sun's luminosity from its photosphere at an effective temperature of 6,019 K.

Name HD 117618, and its planet HD 117618b, were chosen as part of the 2019 NameExoWorlds campaign organised by the International Astronomical Union, which assigned each country a star and planet to be named. HD 117618 was assigned to Indonesia. The winning proposal named the star "Dofida" meaning our star in Nias language, and its planet "Noifasui" meaning revolve around in Nias language (derived from the word ifasui, meaning to revolve around, and no, indicating that the action occurred in the past and continued to the present time).

Planetary system In 2005, the Anglo-Australian Planet Search program announced the discovery of a low-mass planet in orbit around HD 117618. This object was found through measurements of radial velocity variation, which were larger than those produced by the intrinsic jitter of the host star. The best Keplerian fit to the data gave a periodicity of 25.8 days with an eccentricity of around 0.37 and a semimajor axis of 0.17 AU. The lower bound on the object's mass was estimated to be 0.16 MJ. These values were subsequently refined, as shown in the table below.

See also HD 117207 List of extrasolar planets

References

Worked examples

Example 1 — a first encounter with HD 117618

Start with the simplest possible case. Write down what HD 117618 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 117618 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 117618 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 117618

In research: HD 117618 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 117618 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 117618 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Centaurus, Durchmusterung objects, G-type main-sequence stars, so understanding it makes those chapters shorter.
In everyday life: Look for HD 117618 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 117618 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 117618 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 117618 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 117618 in simple terms?

Why does HD 117618 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 117618?

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 117618.