astronomy

RS Persei

RS 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 RS Persei rather than just read about it. In short: RS Persei is a red supergiant variable star located in the Double Cluster in Perseus. The star's apparent magnitude varies from 7.82 to 10.0, meaning it is never visible to the naked eye.

Key takeaways

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

Reference excerpt

RS Persei is a red supergiant variable star located in the Double Cluster in Perseus. The star's apparent magnitude varies from 7.82 to 10.0, meaning it is never visible to the naked eye. It is a member of the cluster NGC 884, χ Persei, one half of the famous Double Cluster.

Variability

In March of 1904, Lidiya Tseraskaya discovered that the star, then referred to as BD+56°583, is a variable star. It was listed with its variable star designation, RS Persei, in Annie Jump Cannon's 1907 work Second Catalog of Variable Stars. RS Persei is classified as a semiregular variable star, with its brightness varying from magnitude 7.82 to 10.0 over 245 days, Detailed studies show that it also pulsates with a long secondary period of 4,200±1,500 days.

Properties RS Persei is a large cool star with a temperature of 3,500 K. Its size makes it luminous, although much of its radiation is emitted in the infrared. In 2005, RS Per was calculated to have a bolometric luminosity of 145,000 L☉ and a radius around 1,000 R☉. More recently, across all wavelengths gives the star a lower luminosity of 77,600+9,500−8,400 L☉, and a radius of 770±30 R☉ based on the distance and the measured angular diameter by the CHARA array. A 2023 paper gives an even smaller luminosity of 59,000 L☉. Estimates based on measured angular diameters and distances estimated by the Gaia DR2 and Gaia DR3 give radii of 547+9−7 R☉ and 775+110−85 R☉. RS Persei has sometimes been considered to be a highly evolved low mass Asymptotic Giant Branch (AGB) star, but calculations of its current mass suggest that it is a true red supergiant. NGC 244 is also too young to host AGB stars.

Illustrations

Worked examples

Example 1 — a first encounter with RS Persei

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

In research: RS 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 RS 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: RS Persei is common in secondary-school and first-year university syllabi. It links to neighbouring topics Durchmusterung objects, Henry Draper Catalogue objects, M-type supergiants, so understanding it makes those chapters shorter.
In everyday life: Look for RS 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 RS Persei in 20 minutes

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

Frequently asked questions

What is RS Persei in simple terms?

RS Persei is a red supergiant variable star located in the Double Cluster in Perseus. The star's apparent magnitude varies from 7.82 to 10.0, meaning it is never visible to the naked eye.

Why does RS 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 RS 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 RS Persei.