astronomy

Tau Herculis

Tau Herculis 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 Tau Herculis rather than just read about it. In short: Tau Herculis, also named Asuusiha (Manchu: ᠠᠰᡠ ᡠᠰᡳᡥᠠ, Möllendorff: asu usiha), is a variable star in the northern constellation of Hercules. It has a blue-white hue and is visible to the naked eye at night with an apparent visual magnitude that fluctuates around 3.91.

Key takeaways

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

Reference excerpt

Tau Herculis, also named Asuusiha (Manchu: ᠠᠰᡠ ᡠᠰᡳᡥᠠ, Möllendorff: asu usiha), is a variable star in the northern constellation of Hercules. It has a blue-white hue and is visible to the naked eye at night with an apparent visual magnitude that fluctuates around 3.91. The star is located at a distance of approximately 307 light-years from the Sun based on parallax, but it is drifting closer with a radial velocity of −16 km/s.

Nomenclature Tau Herculis, Latinized from τ Herculis and abbreviated Tau Her or τ Her, is the star's Bayer designation. In Chinese astronomy, 七公 (Qī Gōng), meaning Seven Excellencies, refers to an asterism consisting of τ Herculis, 42 Herculis, φ Herculis, χ Herculis, ν1 Boötis, μ1 Boötis and δ Boötis. Consequently, the Chinese name for τ Herculis itself is 七公二 (Qī Gōng èr, English: the Second Star of Seven Excellencies). This star is also part of the Manchu constellation Asu Usiha (Manchu: ᠠᠰᡠ ᡠᠰᡳᡥᠠ, Möllendorff: asu usiha), representing a net used to hunt sables. The IAU Working Group on Star Names adopted the name Asuusiha for τ Herculis on 14 May 2026.

Properties

The stellar classification of Tau Herculis is B5 IV, and it serves as a standard spectrum in the modern Morgan–Keenan (MK) classification. It is estimated to be just 26 million years old with a relatively low projected rotational velocity of 32 km/s. Slowly rotating B-type stars are often chemically peculiar, so the mostly normal spectra of this star suggests we may be viewing it from near pole-on. The abundance of most heavier elements in this star are about 85% of those in the Sun. The star has four times the mass of the Sun and around 3.8 times the Sun's radius. On average, it is radiating 574 times the luminosity of the Sun from its photosphere at an effective temperature of 15,615 K. During the Hipparcos mission, Tau Herculis was discovered to be a variable star of the slowly pulsating B-type. These are mid-B main sequence stars that vary with a period of about a day; the brightness of Tau Herculis varies by 0.03 magnitude over a period of 1.24970±0.00008 days. The radial velocity of the star varies at a different rate than the photometric period, with the object showing both radial and non-radial pulsation modes.

Pole star

Tau Herculis is located within 1° of the precessional path traced across the celestial sphere by the Earth's North pole. It could have served the northern pole star around the year 7400 BCE, a phenomenon which is expected to reoccur in the year 18,400 due to precession.

References

Illustrations

Worked examples

Example 1 — a first encounter with Tau Herculis

Start with the simplest possible case. Write down what Tau Herculis 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 Tau Herculis 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 Tau Herculis 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 Tau Herculis

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

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

Frequently asked questions

What is Tau Herculis in simple terms?

Why does Tau Herculis 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 Tau Herculis?

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 Tau Herculis.