astronomy

S Crateris

S 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 S Crateris rather than just read about it. In short: S Crateris (also designated S Crt) is a semiregular variable star of subtype SRb located in the Crater constellation. It is an asymptotic giant branch (AGB) star with a spectral type of M6e-M7e.

Key takeaways

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

Reference excerpt

S Crateris (also designated S Crt) is a semiregular variable star of subtype SRb located in the Crater constellation. It is an asymptotic giant branch (AGB) star with a spectral type of M6e-M7e. The star was discovered to vary in brightness by Williamina Fleming in 1906.

Observation S Crateris is situated at right ascension 11h 52m 45.098s, declination −07° 35′ 48.08″ (J2000.0). Its apparent magnitude in the V band varies between approximately 8.64 and 9.51, giving an amplitude of about 0.87 mag. In the infrared, the star is considerably brighter: the 2MASS catalog lists magnitudes of J = 2.055, H = 1.127, and K = 0.786.

Variability S Crateris is classified as a semiregular variable of type SRb in both the General Catalogue of Variable Stars and the AAVSO Variable Star Index. Its pulsation period is 155 days. The optical light curve in the V band exhibits a variation of approximately 0.8 magnitudes. The reference epoch is HJD 2452284.2 (9 January 2002).

Distance The distance to S Crateris has been the subject of several independent measurements that yielded notably inconsistent results prior to modern VLBI observations. Early estimates based on the period-luminosity relation of Mira variables placed the star at distances of 285 and 420 pc. The original Hipparcos Catalogue measured a parallax of 2.04±1.31 mas, corresponding to a distance of approximately 490 pc, but with a large uncertainty. The revised Hipparcos reduction by van Leeuwen (2007) yielded a parallax of 1.26±0.92 mas, corresponding to a distance of roughly 794 pc.

Proper motion The absolute proper motion of S Crateris, derived from VERA observations after subtracting the internal motion of the reference maser spot, is (μα, μδ) = (−3.17±0.22, −5.41±0.22 mas/yr. This is consistent with the value reported in the revised Hipparcos catalog of (−3.37±1.00, −4.68±0.75) mas/yr. The SIMBAD database lists proper motion values of −3.520 and −5.084 mas/yr from the Gaia-based catalog. The heliocentric radial velocity is 43.55 km/s.

Water masers and circumstellar outflow S Crateris hosts a water maser source at 22 GHz. The stellar systemic LSR velocity is 37.85 km s−1. VERA observations conducted from October 2005 to May 2007 detected internal motions of 26 individual maser spots, with a typical transverse speed of 5.56 km s−1. Analysis of the three-dimensional velocity field revealed a bipolar outflow with its major axis oriented along the northeast–southwest direction, at a position angle of approximately 255°. The outflow axis is inclined at approximately 43° to the plane of the sky, with the southwestern lobe directed away from the observer. The projected maser distribution radius of 14.2 ± 3.5 mas corresponds to a linear radius of 8.96 AU at the adopted distance of 430 pc. The maser flux at 34.7 km s−1 underwent a radio flare beginning in February 2006, reaching a peak of 371 Jy on 31 March 2006, before declining to approximately 60 Jy by July 2006.

References

Worked examples

Example 1 — a first encounter with S Crateris

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

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

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

Frequently asked questions

What is S Crateris in simple terms?

S Crateris (also designated S Crt) is a semiregular variable star of subtype SRb located in the Crater constellation. It is an asymptotic giant branch (AGB) star with a spectral type of M6e-M7e.

Why does S 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 S 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 S Crateris.