astronomy

Sigma Boötis

Sigma Boötis 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 Boötis rather than just read about it. In short: Sigma Boötis, also named Genghe, is a single, yellow-hued star in the northern constellation of Boötes. This star is visible to the naked eye with an apparent visual magnitude of 4.46.

Key takeaways

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

Reference excerpt

Sigma Boötis, also named Genghe, is a single, yellow-hued star in the northern constellation of Boötes. This star is visible to the naked eye with an apparent visual magnitude of 4.46. Located to the southeast of Rho Boötis, the dwarf Sigma may at first appear as a naked-eye double, but the angular proximity with Rho is merely line-of-sight. Sigma Boötis is located at a distance of 51.4 light-years (16 pc) from the Sun based on parallax. The star has a relatively high proper motion and is traversing the sky at the rate of 0.230″ yr−1.

Nomenclature Sigma Boötis is a Bayer designation that is Latinized from σ Boötis, and abbreviated Sigma Boo or σ Boo. It is known by several other catalog designations, including 28 Boötis, BD+30°2536, GC 19659, GJ 557, HD 128167, HIP 71284, HR 5447, SAO 83416, and CCDM 14347+2945. In Chinese astronomy, 梗河 (Gěng Hé), meaning Celestial Lance, refers to an asterism consisting of σ Boötis, ε Boötis and ρ Boötis. Consequently, the Chinese name for σ Boötis itself is 梗河二 (Gěng Hé èr, English: the Second Star of Celestial Lance). The IAU Working Group on Star Names approved the name Genghe for this star on 15 April 2026, after the Chinese asterism.

Properties The stellar classification of Sigma Boötis is F4VkF2mF1. This notation is used for so-called "metal-weak" stars; Am stars with absorption lines of some metals weaker than expected in comparison with other spectral features. The 'F4V', indicating an F-type main-sequence star, is derived from the hydrogen spectral lines and the shape of the metallic lines, the 'kF2' means it has the Calcium K line strength of a hotter F2 star and 'mF1' showing it has the metallic line strength of an F1 star. It is around twice as luminous as a comparable zero age main sequence star, which may indicate it is near the end of its main sequence lifetime. Sigma Boötis is a solar-type star but is larger and more massive than the Sun. It has an estimated age of around two to three billion years and is spinning with a projected rotational velocity of 7 km/s. There is some evidence of variation in radial velocity as well as rotational modulation of active latitudes. Even though the outer convective zone of the star only occupies a few percent of the stellar radius, a surface magnetic field has been detected with a strength of 1.4±0.4 Gauss. This surface field forms a relatively simple dipole topology. The star is radiating 3.5 times the luminosity of the Sun from its photosphere at an effective temperature of 6,594 K. It appears to be a source for X-ray emission. Infrared surveys with the Spitzer and Herschel space telescopes failed to detect an infrared excess around this star at wavelengths up to 160 μm. However, the HOSTS Survey with the Large Binocular Telescope reported a detection of an excess in the far infrared, indicating the presence of exozodiacal dust near the habitable zone of the star.

References

External links HR 5447 CCDM J14347+2945 Image Sigma Boötis

Illustrations

Worked examples

Example 1 — a first encounter with Sigma Boötis

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

In research: Sigma Boötis 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 Boötis 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 Boötis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Am stars, Bayer objects, Boötes, so understanding it makes those chapters shorter.
In everyday life: Look for Sigma Boötis 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 Boötis in 20 minutes

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

Frequently asked questions

What is Sigma Boötis in simple terms?

Sigma Boötis, also named Genghe, is a single, yellow-hued star in the northern constellation of Boötes. This star is visible to the naked eye with an apparent visual magnitude of 4.46.

Why does Sigma Boötis 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 Boötis?

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 Boötis.