astronomy

Phi Virginis

Phi Virginis 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 Phi Virginis rather than just read about it. In short: Phi Virginis (φ Virginis, abbreviated Phi Vir, φ Vir) is a binary star in the zodiac constellation of Virgo. It can be seen with the naked eye, having an apparent visual magnitude of +4.81.

Key takeaways

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

Reference excerpt

Phi Virginis (φ Virginis, abbreviated Phi Vir, φ Vir) is a binary star in the zodiac constellation of Virgo. It can be seen with the naked eye, having an apparent visual magnitude of +4.81. Based upon parallax measurements obtained during the Gaia mission, it is located roughly 121 light-years (37 parsecs) distant from the Sun. The two components are designated Phi Virginis A (officially named Elgafar , the traditional name for the system) and B.

Nomenclature φ Virginis (Latinised to Phi Virginis) is the binary's Bayer designation. The designations of the two components as Phi Virginis A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU). Ideler described an Arabic lunar mansion "El-ġafr" (Arabic الغفر al-ghafr) for the stars Phi, Iota and Kappa Virginis. In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name Elgafar for the component Phi Virginis A on 1 June 2018 and it is now so included in the List of IAU-approved Star Names. In Chinese, 亢宿 (Kàng Xiù), meaning Neck, refers to an asterism consisting of Phi Virginis, Kappa Virginis, Iota Virginis, and Lambda Virginis. Consequently, Phi Virginis itself is known as 亢宿三 (Wěi Xiù sān), "the Third Star of Neck".

Properties The primary component, Phi Virginis A, has a stellar classification of G2 IV, indicating that it is a G-type subgiant which is evolving away from the main sequence. It is slightly variable with an amplitude of 0m.06. The star has about 1.8 times the mass of the Sun, 4 times the Sun's radius, and shines with 12.6 times the luminosity of the Sun. It is around 1.5 billion years old and is spinning with a projected rotational velocity of 15.5 km/s. The effective temperature of the star's outer atmosphere is 5,534 K. The secondary, Phi Virginis B, is a magnitude 9.10 companion at an angular separation of 5.160 arcseconds. A second visual companion lies at an angular separation of 91.40 arcseconds along a position angle of 202°, as of 2000. The system is a source of X-ray emission with a luminosity of 2.158×1020 erg/s.

References

Illustrations

Worked examples

Example 1 — a first encounter with Phi Virginis

Start with the simplest possible case. Write down what Phi Virginis 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 Phi Virginis 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 Phi Virginis 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 Phi Virginis

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

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

Frequently asked questions

What is Phi Virginis in simple terms?

Phi Virginis (φ Virginis, abbreviated Phi Vir, φ Vir) is a binary star in the zodiac constellation of Virgo. It can be seen with the naked eye, having an apparent visual magnitude of +4.81.

Why does Phi Virginis 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 Phi Virginis?

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 Phi Virginis.