astronomy

Omicron Sagittarii

Omicron Sagittarii 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 Omicron Sagittarii rather than just read about it. In short: Omicron Sagittarii, also named Alqiladah, is a single star in the constellation Sagittarius. It is yellow in hue and visible to the naked eye with an apparent visual magnitude of +3.77.

Key takeaways

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

Reference excerpt

Omicron Sagittarii, also named Alqiladah, is a single star in the constellation Sagittarius. It is yellow in hue and visible to the naked eye with an apparent visual magnitude of +3.77. The distance to this star is approximately 142 light years based on parallax. It is drifting further away from the Sun with a radial velocity of +26 km/s, having come to within 86 ly around a million years ago.

Observation This object is positioned 0.86 degrees north of the ecliptic, so ο Sagittarii can be occulted by the Moon and very rarely by planets. The last occultation by a planet took place on 24 December 1937, when it was occulted by Mercury. It was almost eclipsed by the sun, which occupies a mean, rounded, half of one degree of the sky, on 5 January. Thus the star can be viewed the whole night, crossing the sky, in early July.

Nomenclature ο Sagittarii, Latinized as Omicron Sagittarii, is the star's Bayer designation. It is occasionally called by the name Manubrium, usually in an astrological context. This star is part of the Arabic asterism al-Qilāda (القِلادَة) "the necklace"; the IAU Working Group on Star Names adopted the name Alqiladah for this star on 13 August 2026. In Chinese astronomy, 建 (Jiàn), meaning Establishment, refers to an asterism consisting of ο Sagittarii ξ² Sagittarii, π Sagittarii, 43 Sagittarii, ρ¹ Sagittarii and υ Sagittarii. Consequently, the Chinese name for ο Sagittarii itself is 建二 (Jiàn èr, English: the Second Star of Establishment.)

Properties This is an aging giant star with a stellar classification of G9IIIb. It is classified as a red clump giant, suggesting it is on the horizontal branch undergoing core helium fusion. The star is 2.39 billion years old with 1.80 times the mass of the Sun. It has expanded to 12 times the radius of the Sun and is radiating 67 times the Sun's luminosity from its swollen photosphere at an effective temperature of 4,744 K. It has a faint, magnitude 13.8 companion, designated component B and positioned 38.4″ away along a position angle of 252°, as of 2010.

References

Illustrations

Worked examples

Example 1 — a first encounter with Omicron Sagittarii

Start with the simplest possible case. Write down what Omicron Sagittarii 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 Omicron Sagittarii 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 Omicron Sagittarii 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 Omicron Sagittarii

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

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

Frequently asked questions

What is Omicron Sagittarii in simple terms?

Omicron Sagittarii, also named Alqiladah, is a single star in the constellation Sagittarius. It is yellow in hue and visible to the naked eye with an apparent visual magnitude of +3.77.

Why does Omicron Sagittarii 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 Omicron Sagittarii?

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 Omicron Sagittarii.