astronomy

HD 85945

HD 85945 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 85945 rather than just read about it. In short: HD 85945 (HR 3922) is a star in the constellation Ursa Major. It is a yellow giant star with a spectral type of G6III:Fe-0.5.

Key takeaways

HD 85945 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 85945 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 85945 from memory before moving on to harder problems.

Reference excerpt

HD 85945 (HR 3922) is a star in the constellation Ursa Major. It is a yellow giant star with a spectral type of G6III:Fe-0.5. Based on information from Gaia DR3, it is located 132.54 parsecs (432.3 ly) from Earth and is moving towards Earth at a velocity of 47 km/s. It has an apparent magnitude of 5.96, which makes it faintly visible to the naked eye.

Characteristics It is an evolved G-type giant star, based on its spectral type of G6III:Fe-0.5, which also indicates that it has a [Fe/H] metallicity of -0.5. HD 85945 is 2.5 times more massive than the Sun and has expanded to 10.28 times the Sun's size. It is emitting 78 times the solar luminosity from its photosphere at an effective temperature of 5,281 K. Currently, the star is located in the horizontal branch stage of evolution. The age of HD 85945 is estimated at 660 million years, and it rotates under its axis at a speed of 7.53 km/s. It is slightly metal-poor compared to the Sun, with an abundance of iron equivalent to 40% of the solar abundance. HD 85945 is located within the Ursa Major constellation. The distance to HD 85945 is of 132.54 parsecs (432.3 ly), based on spectra from Gaia DR3. The apparent magnitude of the star is of 5.96, which is brighter than the limiting magnitude for naked-eye vision (6.5m), making it faintly visible to the naked eye. The absolute magnitude, i.e. the brightness of the star if it was seen at a distance of 10 parsecs (32.6 ly), is 0.32. At the current distance, its brightness is diminished by 0.03 magnitudes due to interstellar extinction between Earth and the star. HD 85945 is moving away from Earth at a velocity of 46.55 km/s. It has a high proper motion in the sky.

Notes

References

Worked examples

Example 1 — a first encounter with HD 85945

Start with the simplest possible case. Write down what HD 85945 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 85945 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 85945 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 85945

In research: HD 85945 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 85945 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 85945 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bright Star Catalogue objects, G-type giants, Henry Draper Catalogue objects, so understanding it makes those chapters shorter.
In everyday life: Look for HD 85945 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 85945 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 85945 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 85945 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 85945 in simple terms?

HD 85945 (HR 3922) is a star in the constellation Ursa Major. It is a yellow giant star with a spectral type of G6III:Fe-0.5.

Why does HD 85945 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 85945?

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 85945.