astronomy

Psi Persei

Psi 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 Psi Persei rather than just read about it. In short: Psi Persei (Psi Per, ψ Persei, ψ Per) is a single Be star in the northern constellation of Perseus. It has an apparent visual magnitude of about 4.2, so it is visible to the naked eye at night under suitably dark skies.

Key takeaways

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

Reference excerpt

Psi Persei (Psi Per, ψ Persei, ψ Per) is a single Be star in the northern constellation of Perseus. It has an apparent visual magnitude of about 4.2, so it is visible to the naked eye at night under suitably dark skies. Based on parallax measurements, it is located at a distance of roughly 580 light-years (180 parsecs) from the Earth.

Properties

This star has a stellar classification of B5Ve, which indicates it is a B-type main sequence star that is generating energy at its core through the nuclear fusion of hydrogen. It is a shell star with a circumstellar disc of gas surrounding the equator and extending out to about 11 times the radius of the star. As a result of this disc, the spectrum of this star shows emission lines (as indicated by the 'e' in the stellar class) and its magnitude varies over a period 1.021 days. The General Catalog of Variable Stars classifies Psi Persei as a gamma Cassiopeiae variable star, whose visual band brightness varies from magnitude 4.17 to 4.28. Psi Persei is rotating rapidly with a projected rotational velocity (v sin i) along the equator of 390 km/s or more. The axis of rotation is inclined about 75° ± 8° to the line of sight from the Earth, so this velocity is close to the actual azimuthal velocity along the star's equator. It is expelling mass at the rate of about 5.0 × 10−8 times the mass of the Sun per year, or the equivalent of the Sun's mass every 20 million years. The rapid rotation causes Psi Persei to be an oblate shape, with the equatorial radius being 7.3 R☉ and the polar radius to be 5.5 R☉. This star may be a member of the Alpha Persei Cluster, although its proper motion is high compared to other members. Membership probabilities of 26% and 50% have been published from GALAH plus APOGEE data and from Gaia Data Release 2 data respectively.

Name and etymology This star, together with δ Per, σ Per, α Per, γ Per and η Per, has been called the Segment of Perseus. In Chinese, 天船 (Tiān Chuán), meaning Celestial Boat, refers to an asterism consisting of ψ Persei, η Persei, α Persei, γ Persei, δ Persei, 48 Persei, μ Persei and HD 27084. Consequently, the Chinese name for ψ Persei itself is 天船四 (Tiān Chuán sì, English: the Fourth Star of Celestial Boat.)

References

Illustrations

Worked examples

Example 1 — a first encounter with Psi Persei

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

In research: Psi 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 Psi 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: Psi Persei is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alpha Persei Cluster, Bayer objects, Be stars, so understanding it makes those chapters shorter.
In everyday life: Look for Psi 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Psi Persei” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Psi Persei in 20 minutes

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

Frequently asked questions

What is Psi Persei in simple terms?

Why does Psi 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 Psi 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 Psi Persei.