astronomy

HD 128717

HD 128717 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 128717 rather than just read about it. In short: HD 128717 is a star in the constellation of Draco. With an apparent magnitude of +8.29, it is too faint to be seen with the naked eye.

Key takeaways

HD 128717 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 128717 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 128717 from memory before moving on to harder problems.

Reference excerpt

HD 128717 is a star in the constellation of Draco. With an apparent magnitude of +8.29, it is too faint to be seen with the naked eye. Parallax measurements by the Gaia spacecraft imply a distance of 240 light-years (73.7 parsecs). It is moving towards the Solar System at a velocity of 4.851 km/s.

Characteristics With a spectral class of F8, HD 128717 is a late-type F-type star. It is estimated to be 1.4 billion years old, has 1.21 times the mass of the Sun and 1.25 times the radius. It radiates 2.1 times the Sun's luminosity from its photosphere at an effective temperature of 6,210 K, giving it the typical yellowish-white hue of a late-type F-type star. The space velocity components of HD 128717 are U =−30, V=−10 and W=−4km/s. It is orbiting the Milky Way galaxy with an orbital eccentricity of 0.06. Its distance from the Galactic Center varies between 7.40 kiloparsecs (24.1 kilolight-years) and 8.38 kpc (27.3 kly). This orbit lies close to the galactic plane, and the star travels no more than 70 parsecs (230 light-years) above or below this plane.

Companion Astrometric data collected by the Gaia spacecraft on its third data release revealed that HD 128717 appears to wobble around an empty space, indicating that it has an object in orbit whose gravitational force is pulling it. The object was first noted by the Gaia team in 2022, and the paper by Sahlmann et al in 2024 identified HD 128717 "as a strong candidate for hosting a super-Jupiter". In the same year, Alessandro Sozzetti reported, in a conference, the confirmation of the object using radial velocity observations. The companion was independently confirmed by Pinamonti et al. (2025), which named it as Gaia-6b since it was the sixth planetary candidate detected by Gaia that has been later confirmed. HD 128717 b is a brown dwarf with 19.8 times the mass of Jupiter. It has an orbital period of 9.37 years and a highly-eccentric orbit: At apoastron, its orbital separation is 9.0 astronomical units, while at periastron it is 0.73 au. The reasons for such a high eccentricity remain unclear.

Notes

References

Worked examples

Example 1 — a first encounter with HD 128717

Start with the simplest possible case. Write down what HD 128717 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 128717 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 128717 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 128717

In research: HD 128717 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 128717 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 128717 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Brown dwarfs, Draco (constellation), Durchmusterung objects, so understanding it makes those chapters shorter.
In everyday life: Look for HD 128717 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 128717 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 128717 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 128717 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 128717 in simple terms?

HD 128717 is a star in the constellation of Draco. With an apparent magnitude of +8.29, it is too faint to be seen with the naked eye.

Why does HD 128717 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 128717?

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 128717.