astronomy

Gliese 809

Gliese 809 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 809 rather than just read about it. In short: Gliese 809 is a red dwarf star in the constellation Cepheus. A visual magnitude of 8.55 makes it too faint to see with the naked eye.

Key takeaways

Gliese 809 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 809 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Gliese 809 from memory before moving on to harder problems.

Reference excerpt

Gliese 809 is a red dwarf star in the constellation Cepheus. A visual magnitude of 8.55 makes it too faint to see with the naked eye. It is part of the Gliese Catalogue of Nearby Stars and is located about 23 light-years (ly) from the Solar System. Gliese 809 has about 70.5% the radius of the Sun and 61.4% of the Sun's mass. It has a metallicity of −0.06, which means that the abundance of elements other than hydrogen and helium is just 87.1% that of the Sun. This is a high proper motion star that moves about 0.77 arcseconds per year relative to background stars. In physical terms it is travelling with a space velocity of 31.1 km/s relative to the Solar System. The galactic orbit of this star carries it 21,300 ly from the Galactic Center at its perigee to 30,600 ly at its apogee. The orbital eccentricity is 17.8% with the semi-major axis of 25,956 ly and a semi-minor axis of 25,542 ly. Gliese 809 forms an optical double with the 9th magnitude star BD+61°2067, but this is an unrelated background star.

See also List of nearest stars and brown dwarfs

References

Worked examples

Example 1 — a first encounter with Gliese 809

Start with the simplest possible case. Write down what Gliese 809 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 809 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 809 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 809

In research: Gliese 809 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 809 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 809 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cepheus (constellation), Durchmusterung objects, Gliese and GJ objects, so understanding it makes those chapters shorter.
In everyday life: Look for Gliese 809 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 809 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Gliese 809 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 809 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Gliese 809 in simple terms?

Gliese 809 is a red dwarf star in the constellation Cepheus. A visual magnitude of 8.55 makes it too faint to see with the naked eye.

Why does Gliese 809 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 809?

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 809.