astronomy

Mirach

Mirach 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 Mirach rather than just read about it. In short: Mirach is a prominent star in the northern constellation of Andromeda. It is pronounced and has the Bayer designation Beta Andromedae, which is Latinized from β Andromedae.

Key takeaways

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

Reference excerpt

Mirach is a prominent star in the northern constellation of Andromeda. It is pronounced and has the Bayer designation Beta Andromedae, which is Latinized from β Andromedae. This star is positioned northeast of the Great Square of Pegasus and is potentially visible to all observers north of latitude 54° S. It is commonly used by stargazers to find the Andromeda Galaxy. The galaxy NGC 404, also known as Mirach's Ghost, is seven arcminutes away from Mirach. This star has an apparent visual magnitude that varies between 2.01 and 2.10, which at times makes it the brightest star in the constellation. Based upon parallax measurements, it is roughly 197 light-years (60 parsecs) from the Solar System. Its apparent magnitude is reduced by 0.06 by extinction due to gas and dust along the line of sight. The star has a negligible radial velocity of 0.1 km/s, but with a relatively large proper motion, traversing the celestial sphere at an angular rate of 0.208″·yr−1.

Properties

Mirach is a single, aging red giant with a stellar classification of M0 III. It is currently on the asymptotic giant branch of its evolution. The star has an estimated 2.49 times the mass of the Sun. Having exhausted the supply of hydrogen at its core, the outer envelope of the star has expanded to around 86 times the size of the Sun. It is radiating 1,675 times the luminosity of the Sun at an effective temperature of 3,762 K. Mirach is suspected of being a semiregular variable star, with an apparent visual magnitude varies from +2.01 to +2.10. Since 1943 the spectrum of this star has been one of the stable anchor points by which other stars are classified.

Nomenclature Beta Andromedae is the star's Bayer designation. It had the traditional name of Mirach, and its variations, such as Mirac, Mirar, Mirath, Mirak, etc. (the name is spelled Merach in Burritt's The Geography of the Heavens), which come from the star's description in the Alfonsine Tables of 1521 as super mizar. Here, mirat is a corruption of the Arabic مئزر mīzar "girdle", which appeared in a Latin translation of the Almagest. This word refers to Mirach's position at the left hip of the princess Andromeda. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Mirach for this star. Mirach is listed in the Babylonian MUL.APIN as KA.MUSH.I.KU.E, meaning "the Deleter" (the alternative star is α Cas). Medieval astronomers writing in Arabic called Mirach Janb al-Musalsalah (English: The Side of the Chained (Lady)); it was part of the 28th manzil (Arabian lunar mansion) Baṭn al-Ḥūt, the Belly of the Fish, or Qalb al-Ḥūt, the Heart of the Fish. The star has also been called Cingulum and Ventrale. This al-Ḥūt was an indigenous Arabic constellation, not the Western "Northern Fish" part of the constellation Pisces. These names are not from the Arabic marāqq, loins, because it was never called al-Marāqq in Arabian astronomy. Al Rishā', the Cord (of the well-bucket), on al-Sūfī's star map. It is the origin of the proper name Alrescha for Alpha Piscium. In Chinese, 奎宿 (Kuí Sù), meaning Legs, refers to an asterism consisting of Mirach (β Andromedae), η Andromedae, 65 Piscium, ζ Andromedae, ε Andromedae, δ Andromedae, π Andromedae, ν Andromedae, μ Andromedae, σ Piscium, τ Piscium, 91 Piscium, υ Piscium, φ Piscium, χ Piscium and ψ1 Piscium. Consequently, the Chinese name for β Andromedae itself is 奎宿九 (Kuí Sù jiǔ, English: the Ninth Star of Legs). Mirach was considered the standard "black" star; black could mean "dark red" in this context, especially in comparison to Antares, the standard red star. The people of Micronesia named this star Kyyw, meaning "The Porpoise", and this was used as one of the names of the months in Micronesia.

Substellar companion A 2023 study detected radial velocity variations in Mirach (HD 6860), showing evidence of a substellar companion, likely a brown dwarf.

References

Further reading Davis Jr., G. A., (1971) Pronunciations, Derivations, and Meanings of a Selected List of Star Names, (rep.) Cambridge, Sky Publishing Corp. Kunitzsch, P., (1959) Arabische Sternnamen in Europa Kunitzsch. P., (ed.) (1990) Der Sternkatalog des Almagest, Band II

External links Kaler, James B., Mirach, retrieved 2021-05-28. Image MIRACH

Mirach on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

Illustrations

Worked examples

Example 1 — a first encounter with Mirach

Start with the simplest possible case. Write down what Mirach 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 Mirach 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 Mirach 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 Mirach

In research: Mirach 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 Mirach 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: Mirach is common in secondary-school and first-year university syllabi. It links to neighbouring topics Andromeda (constellation), Asymptotic-giant-branch stars, Bayer objects, so understanding it makes those chapters shorter.
In everyday life: Look for Mirach 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 Mirach in 20 minutes

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

Frequently asked questions

What is Mirach in simple terms?

Mirach is a prominent star in the northern constellation of Andromeda. It is pronounced and has the Bayer designation Beta Andromedae, which is Latinized from β Andromedae.

Why does Mirach 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 Mirach?

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 Mirach.