astronomy

HD 90156

HD 90156 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 90156 rather than just read about it. In short: HD 90156 is a star with an orbiting exoplanet in the constellation Hydra. Based on parallax measurements, it is located at a distance of 71.6 light-years from the Sun.

Key takeaways

HD 90156 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 90156 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 90156 from memory before moving on to harder problems.

Reference excerpt

HD 90156 is a star with an orbiting exoplanet in the constellation Hydra. Based on parallax measurements, it is located at a distance of 71.6 light-years from the Sun. The system is drifting further away with a heliocentric radial velocity of 27 km/s. The apparent visual magnitude of this star is 6.92, which is places it near the lower limit of visibility to the naked eye. A survey in 2015 ruled out the existence of any stellar companions at projected distances above 5 AU. This star was designated as Gamma Antliae by Lacaille, and Gould intended to keep it in the Antlia constellation. However, the delineating of constellation boundaries in 1930 saw it transferred to Hydra. The spectrum of HD 90156 presents as a G-type main-sequence star with a stellar classification of G5 V It is rotating slowly with a projected rotational velocity of 0.817, and it only displays a low level of magnetic activity in its chromosphere. The metallicity of the star is lower than in the Sun, indicating a paucity of elements with mass greater than helium. The star has 84% of the mass of the Sun and 88% of the Sun's radius. It is radiating 74% of the Sun's luminosity from its photosphere at an effective temperature of 5,599 K.

Planetary system In 2011, an exoplanet was found in an eccentric orbit around the host star using Doppler spectroscopy. As the inclination of its orbital plane is unknown, only a lower bound on its mass can be determined. It has at least 18 times the mass of the Earth. The exoplanet is orbiting its host star with a separation of 0.25 AU and a period of 50 days.

Worked examples

Example 1 — a first encounter with HD 90156

Start with the simplest possible case. Write down what HD 90156 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 90156 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 90156 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 90156

In research: HD 90156 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 90156 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 90156 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bayer objects, Durchmusterung objects, G-type main-sequence stars, so understanding it makes those chapters shorter.
In everyday life: Look for HD 90156 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 90156 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 90156 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 90156 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 90156 in simple terms?

HD 90156 is a star with an orbiting exoplanet in the constellation Hydra. Based on parallax measurements, it is located at a distance of 71.6 light-years from the Sun.

Why does HD 90156 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 90156?

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 90156.