astronomy

Sigma Aquilae

Sigma Aquilae 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 Aquilae rather than just read about it. In short: Sigma Aquilae, also named Hru, is an eclipsing binary star system in the equatorial constellation of Aquila. Its Bayer designation is Latinized from σ Aquilae, and abbreviated Sigma Aql or σ Aql.

Key takeaways

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

Reference excerpt

Sigma Aquilae, also named Hru, is an eclipsing binary star system in the equatorial constellation of Aquila. Its Bayer designation is Latinized from σ Aquilae, and abbreviated Sigma Aql or σ Aql. The baseline apparent visual magnitude of the pair is +5.17, which, according to the Bortle Dark-Sky Scale, is bright enough to be seen with the naked eye from suburban skies. Because of the Earth's orbit about the Sun, this system has an annual parallax shift of 4.16 mas. This provides a distance estimate of approximately 780 light-years (240 parsecs). The system is drifting closer to the Sun with a radial velocity of −5 km/s.

Sigma Aquilae is a double-lined spectroscopic binary system consisting of two intermediate-mass B-type main sequence stars; each has a stellar classification of B3 V. They are detached components, which means the two stars are sufficiently distant from each other that neither fills its Roche lobe. Their close, circular orbit has a period of 1.95 days with a semimajor axis of 14.3 times the radius of the Sun. Because the orbital plane lies close to the line of sight with the Earth, they form an eclipsing binary system. The two components are each distorted by the gravity of the other star, and their shapes mean that the magnitude of the star system varies constantly even outside of the eclipses, an arrangement known as a Beta Lyrae variable. The brightness of the pair decreases during each eclipse, which occurs with a frequency determined by their orbital period of 1.95028 days. During the eclipse of the primary component the magnitude decreases by 0.20 to a net of 5.37; the eclipse of the secondary component results in a magnitude decrease of 0.10 to a net of 5.27. The primary component has 5.8 times the mass of the Sun and 3.7 times the Sun's radius. It is radiating 1,862 times the luminosity of the Sun from its photosphere at an effective temperature of 18,493 K. The smaller secondary has 4.6 times the mass, 3.3 times the radius, and 524 times the luminosity of the Sun. Its outer atmosphere has an effective temperature of 15,848 K. This star has a high rate of spin, showing a projected rotational velocity of 120 km/s. In Bali (Indonesia), Ru or Hru refers to a constellation of an arrow, corresponding to Aquila; the term is derived from Sanskrit. The IAU Working Group on Star Names adopted the name Hru for this star on 18 June 2026.

References

External links Image ADS 12737 HR 7474 CCDM 19392+0524

Illustrations

Worked examples

Example 1 — a first encounter with Sigma Aquilae

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

In research: Sigma Aquilae 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 Aquilae 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 Aquilae is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aquila (constellation), B-type main-sequence stars, Bayer objects, so understanding it makes those chapters shorter.
In everyday life: Look for Sigma Aquilae 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 Aquilae in 20 minutes

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

Frequently asked questions

What is Sigma Aquilae in simple terms?

Sigma Aquilae, also named Hru, is an eclipsing binary star system in the equatorial constellation of Aquila. Its Bayer designation is Latinized from σ Aquilae, and abbreviated Sigma Aql or σ Aql.

Why does Sigma Aquilae 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 Aquilae?

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 Aquilae.