astronomy

Lambda Aquarii

Lambda Aquarii 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 Lambda Aquarii rather than just read about it. In short: Lambda Aquarii, Latinized from λ Aquarii and formally named Shatabhisha, is a variable star in the equatorial constellation of Aquarius. The apparent visual magnitude of this star ranges from 3.57 down to 3.80, which is bright enough to be visible with the naked eye.

Key takeaways

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

Reference excerpt

Lambda Aquarii, Latinized from λ Aquarii and formally named Shatabhisha, is a variable star in the equatorial constellation of Aquarius. The apparent visual magnitude of this star ranges from 3.57 down to 3.80, which is bright enough to be visible with the naked eye. The star is eclipsed by the sun from about 1-4 March; thus the star can be viewed the whole night, crossing the sky, in early September, in the current epoch. Lambda Aquarii is located at a distance of 365 light-years (112 pc) from the Sun based on parallax, but is drifting closer with a radial velocity of −10.5 km/s. This star lies just 0.39 degrees south of the ecliptic and so is subject to lunar and planetary occultations. On 16 April 2014, it was occulted by Venus as viewed from Australia, New Zealand and the West Pacific.

Naming The name Lambda Aquarii is Latinized from the Bayer designation λ Aquarii, and abbreviated Lambda Aqr or λ Aqr. This star has been called Hydor () from the ancient Greek Ὕδωρ "water", a name given by Proclus, according to Richard Hinckley Allen. Another Greek name for the star is Ekkhysis, from εκχυσις "outpouring". These names originally referred to a constellation of faint stars in the region of Aquarius and Cetus; they were associated with this star by Bayer's Uranometria (1603) and Allen's Star Names (1899). In Indian astronomy, this is the main star of the nakshatra Śatabhiṣa or Shatabhisha (spelled Catabhisaj by Allen), meaning "a hundred physicians". Some sources instead attribute this name to γ Aquarii (Sadachbia), which is likely a reading or writing error. λ Aquarii also has the Tibetan name Mondru. The IAU Working Group on Star Names approved the name Shatabhisha for λ Aquarii on 22 September 2025 and it is now so entered in the IAU Catalog of Star Names. The name Hydor was officially adopted for another star in the historical constellation, 2 Ceti. In Chinese astronomy, 壘壁陣 (Lěi Bì Zhèn), meaning Line of Ramparts, refers to an asterism consisting of λ Aquarii, κ Capricorni, ε Capricorni, γ Capricorni, δ Capricorni, ι Aquarii, σ Aquarii, φ Aquarii, 27 Piscium, 29 Piscium, 33 Piscium and 30 Piscium. Consequently, λ Aquarii itself is 壘壁陣七 (Lěi Bì Zhèn qī, English: the Seventh Star of Line of Ramparts).

Properties

The stellar classification of Lambda Aquarii is M2.5 IIIa Fe–1, indicating this is an aging red giant star with an underabundance of iron showing in its spectrum. This star is on the asymptotic giant branch and is generating energy through the nuclear fusion of hydrogen and helium along concentric shells surrounding an inert core of carbon and oxygen. With 3.6 times the mass of the Sun, it has expanded to 100 times the Sun's radius. Lambda Aquarii has a magnetic field with an effective strength measured at 220±60 Gauss. It is classified as slow irregular variable and pulsation periods of 24.5, 32.0, and 49.5 days have been identified. On average, it is radiating nearly 1,600 times the luminosity of the Sun from the photosphere at an effective temperature of 3,702 K. A faint companion star was detected by speckle interferometry during observations of a lunar occultation in 2016. It is likely an F-type main-sequence star that is gravitationally bound to Lambda Aquarii.

References

External links Image Lambda Aquarii Named Stars

Illustrations

Worked examples

Example 1 — a first encounter with Lambda Aquarii

Start with the simplest possible case. Write down what Lambda Aquarii 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 Lambda Aquarii 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 Lambda Aquarii 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 Lambda Aquarii

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

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

Frequently asked questions

What is Lambda Aquarii in simple terms?

Why does Lambda Aquarii 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 Lambda Aquarii?

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 Lambda Aquarii.