astronomy

Sigma Persei

Sigma Persei 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 Sigma Persei rather than just read about it. In short: Sigma Persei (Sigma Per, σ Persei, σ Per) is an orange K-type giant star with an apparent magnitude of +4.36. It is approximately 343 light-years from Earth.

Key takeaways

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

Reference excerpt

Sigma Persei (Sigma Per, σ Persei, σ Per) is an orange K-type giant star with an apparent magnitude of +4.36. It is approximately 343 light-years from Earth. Sigma Persei is moving through the Galaxy at a speed of 17.4 km/s relative to the Sun. Its projected Galactic orbit carries it between 24,400 and 43,600 light years from the center of the Galaxy. It came closest to the Sun 5.1 million years ago when it had brightened to magnitude 3.11 from a distance of 202 light years. In 2014 a planet was reported, Sigma Persei b, with a period of 580 days and a mass approximately 6.5 times that of Jupiter. However, a 2025 study found that the observed radial velocity variations are intrinsic to the star, and not caused by a planetary companion.

Name and etymology This star, together with δ Per, ψ Per, α Per, γ Per and η Per, has been called the Segment of Perseus.

References

Illustrations

Worked examples

Example 1 — a first encounter with Sigma Persei

Start with the simplest possible case. Write down what Sigma Persei 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 Sigma Persei 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 Sigma Persei 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 Sigma Persei

In research: Sigma Persei 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 Sigma Persei 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: Sigma Persei is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bayer objects, Bright Star Catalogue objects, Durchmusterung objects, so understanding it makes those chapters shorter.
In everyday life: Look for Sigma Persei 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 Sigma Persei in 20 minutes

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

Frequently asked questions

What is Sigma Persei in simple terms?

Sigma Persei (Sigma Per, σ Persei, σ Per) is an orange K-type giant star with an apparent magnitude of +4.36. It is approximately 343 light-years from Earth.

Why does Sigma Persei 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 Sigma Persei?

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 Sigma Persei.