astronomy

GJ 3998

GJ 3998 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 GJ 3998 rather than just read about it. In short: GJ 3998 is a red dwarf star located 59.3 light-years (18.2 parsecs) away in the constellation Ophiuchus. It has about half the mass and radius of the Sun, and only 4% of its luminosity.

Key takeaways

GJ 3998 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect GJ 3998 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of GJ 3998 from memory before moving on to harder problems.

Reference excerpt

GJ 3998 is a red dwarf star located 59.3 light-years (18.2 parsecs) away in the constellation Ophiuchus. It has about half the mass and radius of the Sun, and only 4% of its luminosity. Its rotation period is 30 days. GJ 3998 hosts a system of three known planets, all super-Earth-mass planets detected by the radial velocity method. The outermost planet, with a minimum mass about six times the mass of Earth, orbits within the optimistic habitable zone. The star rotates with an inclination of >30° to the plane of the sky; if the planetary orbits are coplanar with the star, their true masses are at most twice their minimum masses. The two inner planets were found in 2016, but were questioned by a 2022 study, which argued that the radial velocity signals may instead be due to intrinsic stellar activity. The third planet was found by a 2025 follow-up study by the original discovery team, who did a series of tests on stellar activity signals that they believe validate all three planets.

References

Worked examples

Example 1 — a first encounter with GJ 3998

Start with the simplest possible case. Write down what GJ 3998 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 GJ 3998 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 GJ 3998 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 GJ 3998

In research: GJ 3998 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 GJ 3998 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: GJ 3998 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Durchmusterung objects, Gliese and GJ objects, Hipparcos objects, so understanding it makes those chapters shorter.
In everyday life: Look for GJ 3998 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 GJ 3998 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what GJ 3998 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 GJ 3998 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is GJ 3998 in simple terms?

GJ 3998 is a red dwarf star located 59.3 light-years (18.2 parsecs) away in the constellation Ophiuchus. It has about half the mass and radius of the Sun, and only 4% of its luminosity.

Why does GJ 3998 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 GJ 3998?

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 GJ 3998.