astronomy

Gliese 251

Gliese 251 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 Gliese 251 rather than just read about it. In short: Gliese 251, also known as HIP 33226 or HD 265866, is a star located 18.2 light-years away from the Solar System. Located in the constellation of Gemini, it is the nearest star in this constellation.

Key takeaways

Gliese 251 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Gliese 251 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Gliese 251 from memory before moving on to harder problems.

Reference excerpt

Gliese 251, also known as HIP 33226 or HD 265866, is a star located 18.2 light-years away from the Solar System. Located in the constellation of Gemini, it is the nearest star in this constellation. It is located near the boundary with Auriga, 49 arcminutes away from the bright star Theta Geminorum; due to its apparent magnitude of +9.89 it cannot be observed with the naked eye. The closest star to Gliese 251 is QY Aurigae, which is located 3.5 light years away. Gliese 251 is a red dwarf with a spectral type of M3V with an effective temperature of about 3300 K. Its mass has been measured to be around 0.36 solar masses and its radius is about 36% solar radii. Its metallicity is likely slightly less than that of the Sun. Observations at infrared wavelengths rule out the presence of a circumstellar disk around it.

Planetary system In 2019, two candidate planets were detected by the radial velocity method to orbit Gliese 251 at orbits of 1.74 and 607 days. However, a new study in 2020 using CARMENES data refuted both candidates, as they found that both signals were caused by stellar activity. Based on the CARMENES data, the team announced that Gliese 251 is orbited by one single super-Earth (Gliese 251 b) at an orbit of 14.238 days. In 2025, a second planet (c) was confirmed which is also a super-Earth and orbits within the circumstellar habitable zone. It may be possible to directly image planet c with next-generation telescopes such as the Thirty Meter Telescope.

See also List of exoplanets discovered in 2020 - Gliese 251 b

References

Notes

Worked examples

Example 1 — a first encounter with Gliese 251

Start with the simplest possible case. Write down what Gliese 251 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 Gliese 251 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 Gliese 251 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 Gliese 251

In research: Gliese 251 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 Gliese 251 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: Gliese 251 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Gemini (constellation), Gliese and GJ objects, Henry Draper Catalogue objects, so understanding it makes those chapters shorter.
In everyday life: Look for Gliese 251 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 Gliese 251 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Gliese 251 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 Gliese 251 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Gliese 251 in simple terms?

Gliese 251, also known as HIP 33226 or HD 265866, is a star located 18.2 light-years away from the Solar System. Located in the constellation of Gemini, it is the nearest star in this constellation.

Why does Gliese 251 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 Gliese 251?

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 Gliese 251.