astronomy

HD 108874

HD 108874 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 108874 rather than just read about it. In short: HD 108874 is a star with a pair of orbiting exoplanets in the northern constellation of Coma Berenices. It is located 194.5 light years from the Sun based on parallax measurements, but is drifting closer with a radial velocity of −30 km/s.

Key takeaways

HD 108874 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 108874 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 108874 from memory before moving on to harder problems.

Reference excerpt

HD 108874 is a star with a pair of orbiting exoplanets in the northern constellation of Coma Berenices. It is located 194.5 light years from the Sun based on parallax measurements, but is drifting closer with a radial velocity of −30 km/s. The absolute magnitude of this star is 4.79, but at that distance the star has an apparent visual magnitude of 8.76, making it too faint to be visible to the naked eye. HD 108874 has a relatively large proper motion, traversing the celestial sphere at an angular rate of 0.157″ yr−1. The spectrum of HD 108874 presents as a G-type main-sequence star with a stellar classification of G5 V. (An alternate source gives a class of G9 V.) It is probably billions of years older than the Sun although the age is not well constrained. The level of magnetic activity in the chromosphere is lower than in the Sun and it is spinning with a low rotation period of 40 days. The star has about the same mass as the Sun, but the radius is 6% larger. The abundance of iron, an indicator of the star's metallicity, is 1.18 times that of the Sun. The star is radiating 1.19 times the luminosity of the Sun from its photosphere at an effective temperature of about 5600 K.

Planetary system In 2003, the jovian planet HD 108874 b was discovered by the US-based team led by Paul Butler, Geoffrey Marcy, Steven Vogt, and Debra Fischer. A total of 20 radial velocity observations, obtained at the W. M. Keck Observatory between 1999 and 2002, were used to make the discovery. In 2005, further observations revealed this star has another jovian planet orbiting further out, designated as HD 108874 c. The orbital parameters of both planets were updated in 2009 with additional observations. There is an additional radial velocity signal in the data at a period of 40 days however this likely caused by the stellar rotation period. Those two planets are near, and possibly in a 9:2 orbital resonance. This means if HD 108874 b orbits the star nine times, then HD 108874 c orbits twice, because the orbital period for planet c is four and a half times longer than planet b.

Illustrations

Worked examples

Example 1 — a first encounter with HD 108874

Start with the simplest possible case. Write down what HD 108874 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 108874 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 108874 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 108874

In research: HD 108874 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 108874 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 108874 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Coma Berenices, Durchmusterung objects, G-type main-sequence stars, so understanding it makes those chapters shorter.
In everyday life: Look for HD 108874 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 108874 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 108874 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 108874 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 108874 in simple terms?

Why does HD 108874 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 108874?

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 108874.