astronomy

HD 12661

HD 12661 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 HD 12661 rather than just read about it. In short: HD 12661 is a G-type main sequence star in the northern constellation of Aries. The star is slightly larger and more massive than the Sun, with an estimated age of seven billion years.

Key takeaways

HD 12661 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect HD 12661 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 12661 from memory before moving on to harder problems.

Reference excerpt

HD 12661 is a G-type main sequence star in the northern constellation of Aries. The star is slightly larger and more massive than the Sun, with an estimated age of seven billion years. It has two known extrasolar planets.

Properties The apparent visual magnitude of this star is 7.42, making it too faint to be viewed by the naked eye even under ideal viewing conditions. However, it can be readily observed using a small telescope with an aperture of 6 cm (2 in) or more. Parallax measurements of HD 12661 place it at a distance of about 123.3 light-years (37.8 parsecs) from the Earth, with a margin of error of ±0.1 light years. It has a stellar classification of G6 V, indicating that it is a main sequence star that is generating energy through the thermonuclear fusion of hydrogen at its core. The effective temperature of the star's outer envelope is about 5,754 K, giving it the characteristic yellow hue of a G-type star. Based on stellar models, estimates of the radius of this star range from 107% to 112% times Sun's radius, while the mass is likely in the range from 107% to 110% of the Sun's mass. As a star ages it slows its rotation and diminishes the amount of magnetic activity in its chromosphere. Hence the measured emission from the chromosphere can be used to estimate the age of a star, particularly for F and G-type dwarf stars with an age of less than two billion years. However, this technique becomes less accurate for ages beyond about 5.6 billion years. Based upon the chromosphere emission of HD 12661, it is older than the Sun with an estimated age of roughly seven billion years. It has a low projected rotational velocity of 1.20 km/s, consistent with it being an older star. The age of a star can also be estimated by the abundance of lithium, as this element is destroyed through thermonuclear fusion at the core. However, this is less accurate technique. For HD 12661, the lithium abundance gives an age estimate of 4.4 billion years. The abundance of elements other than hydrogen and helium, what astronomers term the metallicity, is unusually high in this star when compared to the Sun. High metallicity has been found to be statistically correlated with the presence of a multi-planet system around a star. It is possible that a planet in this system may have been scattered and ended up being accreted by the star, which may account for the large surface metallicity.

Planetary system The first planet was discovered in 2001 from the Lick and Keck observatories using precision measurements of the star's radial velocity variations. The periodicity in this variation allowed astronomers to extract information about the planet's orbit and minimum mass. A second planet was discovered by the same team two years later. Both planets are greater in mass than Jupiter. The inclination and true mass of planet c were measured using astrometry, and the results were published in 2025. The system is dynamically unstable. "Either this system is being observed during a relatively rare state, or additional planets are affecting the observed radial velocities and/or the system’s secular eccentricity evolution."

Illustrations

Worked examples

Example 1 — a first encounter with HD 12661

Start with the simplest possible case. Write down what HD 12661 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 HD 12661 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 HD 12661 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 HD 12661

In research: HD 12661 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 HD 12661 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: HD 12661 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aries (constellation), Durchmusterung objects, G-type main-sequence stars, so understanding it makes those chapters shorter.
In everyday life: Look for HD 12661 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 HD 12661 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 12661 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 HD 12661 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 12661 in simple terms?

HD 12661 is a G-type main sequence star in the northern constellation of Aries. The star is slightly larger and more massive than the Sun, with an estimated age of seven billion years.

Why does HD 12661 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 HD 12661?

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 HD 12661.