astronomy

Sh 2-185

Sh 2-185 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 Sh 2-185 rather than just read about it. In short: Sh 2-185 is an H II region centered on the massive star system Gamma Cassiopeiae (γ Cas) in the northern constellation of Cassiopeia. It was included in the second Catalogue of H II Regions, published in 1959 by Stewart Sharpless.

Key takeaways

Sh 2-185 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sh 2-185 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sh 2-185 from memory before moving on to harder problems.

Reference excerpt

Sh 2-185 is an H II region centered on the massive star system Gamma Cassiopeiae (γ Cas) in the northern constellation of Cassiopeia. It was included in the second Catalogue of H II Regions, published in 1959 by Stewart Sharpless. Sh 2-185 is located at a distance of approximately 10,500 ly (3.23 kpc) from the Sun. The region is surrounded by a dust shell, and displays several infrared point sources that are a characteristics of young stellar objects. This H II region includes the reflection and emission nebulae IC 59 and IC 63. Both nebulae have a cometary shape, with IC 63 being the brighter of the two. The difference in appearance between the two nebulae is a consequence of their physical distance from γ Cas. IC 63 displays a well-defined ionization front, while this is lacking in IC 59. The nebulae are the closest photodissociation regions to the Sun.

IC 59

This nebula was discovered by German astronomer Max Wolf on December 30, 1893, then added to J. L. E. Dreyer's Index Catalogue of Nebulae in 1895. It spans an angular size of 10′ and is visible with a small telescope. From the perspective of the Earth, IC 59 is positioned in front of γ Cas, and the closest tip to the star is located at a separation of 13.5 ly (4.15 pc). It is a photodissociation region that is being sculpted by γ Cas. Light from the star is being scattered from the nebula at an angle of 17° toward the Earth. Although the tip of the nebula has been considered the closest point to γ Cas, the western concave face is where the most intense UV radiation is being received. Hence the tip may actually be further away from the star than the rest of the cloud. The warmer component of this nebula has a mean temperature of 675±49 K, while the cooler component is 150±34 K.

IC 63

IC 63 is sometimes dubbed the Ghost Nebula, or the ghost of Cassiopeia. It was discovered by Max Wolf on the same night as IC 59, and has since been extensively studied. It spans an angular size of 10′ and is visible with a small telescope. From the perspective of the Earth, IC 63 is positioned behind γ Cas, and the closest tip to the star is located at a separation of 7.5 ly (2.3 pc). It is a photodissociation region that is being sculpted by γ Cas. Light from the star is being scattered from the nebula at an angle of 154° toward the Earth. There is no evidence of triggered star formation in this nebula. The warmer component of this nebula has a mean temperature of 740±47 K, while the cooler component is 207±30 K. The velocity distribution across the nebula varies with the distance from the star, and is consistent with it being driven by the radiation. The atomic hydrogen in the PDR structure has a clumpy organization, while the tip has a ring-like structure. The entire structure seems to be moving apart and it is likely that this nebula will completely disperse within a half million years.

References

Illustrations

Worked examples

Example 1 — a first encounter with Sh 2-185

Start with the simplest possible case. Write down what Sh 2-185 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 Sh 2-185 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 Sh 2-185 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 Sh 2-185

In research: Sh 2-185 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 Sh 2-185 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: Sh 2-185 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cassiopeia (constellation), Discoveries by Max Wolf, Emission nebulae, so understanding it makes those chapters shorter.
In everyday life: Look for Sh 2-185 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Sh 2-185 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sh 2-185 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 Sh 2-185 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sh 2-185 in simple terms?

Why does Sh 2-185 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 Sh 2-185?

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 Sh 2-185.