astronomy

Tau Boötis

Tau 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 Tau Boötis rather than just read about it. In short: Tau Boötis, Latinised from τ Boötis and formally named Tepiamenit, is a wide binary star system in the northern constellation of Boötes. This system is visible to the naked eye at a point of light with a combined apparent visual magnitude of 4.50.

Key takeaways

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

Reference excerpt

Tau Boötis, Latinised from τ Boötis and formally named Tepiamenit, is a wide binary star system in the northern constellation of Boötes. This system is visible to the naked eye at a point of light with a combined apparent visual magnitude of 4.50. Based on parallax measurements, It is located at a distance of approximately 51 light-years (16 pc) from the Earth. This system is drifting closer to the Sun with a radial velocity of −16 km/s. The primary component is an ordinary F-type main-sequence star that is larger, brighter, and more massive than the Sun, while the secondary is a faint red dwarf. In 1999, an extrasolar planet was detected orbiting the primary star.

Nomenclature Tau Boötis is a Bayer designation that is Latinised from τ Boötis, and abbreviated Tau Boo or τ Boo. The name Tepiamenit, of ancient Egyptian origin, was adopted for the primary component Tau Boötis A, by the IAU Working Group on Star Names on 15 April 2026. Menit, the pole or mooring post, was an ancient Egyptian constellation appearing in the Ramesside star clocks; it marked the northern celestial and ecliptic poles in the 2nd millennium BCE. Tepiamenit, the predecessor of the pole, referred to an asterism in the area of Tau Boötis.

Naming controversy This star and its planet were one of the planetary systems selected by the International Astronomical Union as part of NameExoWorlds, their public process for giving proper names to exoplanets and their host star (where no proper name already exists). The process involved public nomination and voting for the new names, and the IAU announced the new names in mid-December 2015. However, the IAU annulled the vote for this system, as the winning names ("Shri Ram Matt" for the star and "Bhagavatidevi" for the planet) were judged not to conform with the IAU rules for naming exoplanets due to the political activities of the namesake people. The names garnered the majority of the votes cast for the system, and made up a significant proportion of all votes cast as part of the contest. The IAU later assigned the name Tepiamenit to the primary component Tau Boötis A on April 15th 2026.

Stellar components

The primary component is a yellow-white F-type main-sequence star with a stellar classification of F6V. It is 35 percent more massive and 42 percent larger than the Sun. The star is radiating three times the luminosity of the Sun from its photosphere at an effective temperature of 6,387 K. It is about 1.3 billion years old, making it younger than the Sun. Since it is more massive than the Sun, its lifespan is shorter—less than 6 billion years. This star is spinning with a projected rotational velocity of 14.3 km/s, completing a rotation every three days. The primary is the first star apart from the Sun to be observed changing the polarity of its magnetic field. It is listed as a suspected variable star. The magnetic activity cycle for this star shows a period of 122 days—much shorter than the solar cycle. The secondary companion is a dim, 11th magnitude red dwarf of spectral type M2. It only about half the mass and radius of the Sun. The stars orbit each other at a typical distance of about 220 AU (14 arcseconds) but come as close as about 28 AU during periapsis, giving its orbit a very high eccentricity of about 0.87. One orbit around the primary would take approximately 2,400 years to complete, although this period is poorly constrained.

Planetary system

In 1996 the exoplanet Tau Boötis b was discovered orbiting the primary star by a team of astronomers led by R. Paul Butler. It has six times the mass of Jupiter and is orbiting the star with a period of 3.3 days. Tau Boötis and its planet appear to be tidally locked to each other. In 2014, water vapor was discovered in the atmosphere of this hot Jupiter. There are indications of a second planet orbiting the star with a period of roughly 5,000 days; however, this could be due to an instrumental effect or a stellar magnetic activity cycle. Because this is a highly eccentric binary star system, the maximum exoplanetary orbit around the primary that is dynamically stable for long periods has a semimajor axis of 4.86 au.

See also List of exoplanets discovered before 2000 - Tau Boötis b

References

External links "VizieR: HR 5185". Centre de Données astronomiques de Strasbourg. Retrieved 2009-05-15. "VizieR: CCDM J13473+1727". Centre de Données astronomiques de Strasbourg. Retrieved 2009-05-15. "Aladin Previewer: Tau Boötis". Centre de Données astronomiques de Strasbourg. Retrieved 2009-05-15. Schirber, Michael (23 May 2005). "Role Reversal: Planet Controls a Star". SPACE.com. Retrieved 2008-06-25. "Notes for star Tau Boo". Extrasolar Planets Encyclopaedia. Archived from the original on September 29, 2007. Retrieved 2008-06-25. "Tau Boötis 2". SolStation. Archived from the original on November 22, 2001. Retrieved 2008-06-25. "Tau Bootis". The Planet Project. Archived from the original on 2008-05-17. Retrieved 2008-06-25.

Illustrations

Worked examples

Example 1 — a first encounter with Tau Boötis

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

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

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

Frequently asked questions

What is Tau Boötis in simple terms?

Why does Tau 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 Tau 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 Tau Boötis.