astronomy

R Crateris

R Crateris 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 R Crateris rather than just read about it. In short: R Crateris is a star about 700 light years from the Earth in the constellation Crater. It is a semiregular variable star, ranging in brightness from magnitude 8.1 to 9.5 over a period of about 160 days.

Key takeaways

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

Reference excerpt

R Crateris is a star about 700 light years from the Earth in the constellation Crater. It is a semiregular variable star, ranging in brightness from magnitude 8.1 to 9.5 over a period of about 160 days. It is not visible to the naked-eye, but can be seen with a small telescope, or binoculars. R Crateris is a double star; the variable star and its magnitude 9.9 F8V companion are separated by 65.4 arcseconds. Friedrich August Theodor Winnecke discovered that the star is variable in 1861. In 1907 it appeared with its variable star designation, R Crateris, in Annie Jump Cannon's Second Catalog of Variable Stars. Although the period for large brightness changes in R Crateris is listed as ~160 days, in 1982 Silvia Livi and Thaisa Bergmann reported small (~0.1 magnitude) variations on timescales of less than one hour. The rapid variations seem to be more regular when the star is near maximum brightness. R Crateris is an oxygen-rich asymptotic giant branch star, losing mass at a rate of 8×10−7 solar masses per year via a stellar wind. At large distances from the star, the wind is expanding into space at 11.7±0.3 km/s. Near-infrared radiation from R Crateris was detected in the first Two-Micron Sky Survey, published in 1969. It was detected in the far-infrared by the IRAS satellite, and that emission was resolved by IRAS, showing that the star is surrounded by a large circumstellar shell containing dust. High resolution far-infrared images of R Crateris taken by the Herschel Space Observatory show that the emitting region of the shell, roughly 280 arcseconds (0.94 light year) across, consists primarily of two non-concentric arcs well separated from the star itself. The arcs are probably bowshocks formed as the dusty stellar wind collides with the interstellar medium. The total mass of the shell, including both dust and gas, is estimated to be about (6.4±2)×10−2 solar masses. Infrared imaging of the innermost (sub-arcsecond) portion of the dust shell shows a bipolar structure. In the early 1970s, maser emission from OH and H2O was detected in R Crateris' circumstellar shell. SiO maser emission was detected in 1985. Thermal (non-maser) emission from CO was detected in 1986. With the high angular resolution provided by Very Long Baseline Interferometry, the H2O maser emission is seen to arise from small (milli-arcsecond) blobs, whose proper motions through the inner region of the circumstellar shell can be measured. These observations give additional evidence that R Crateris has developed a bipolar stellar wind.

References

Illustrations

Worked examples

Example 1 — a first encounter with R Crateris

Start with the simplest possible case. Write down what R Crateris 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 R Crateris 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 R Crateris 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 R Crateris

In research: R Crateris 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 R Crateris 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: R Crateris is common in secondary-school and first-year university syllabi. It links to neighbouring topics Asymptotic-giant-branch stars, Crater (constellation), Henry Draper Catalogue objects, so understanding it makes those chapters shorter.
In everyday life: Look for R Crateris 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 R Crateris in 20 minutes

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

Frequently asked questions

What is R Crateris in simple terms?

Why does R Crateris 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 R Crateris?

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 R Crateris.