astronomy

Sharpless catalog

Sharpless catalog 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 Sharpless catalog rather than just read about it. In short: The Sharpless catalog is a list of 313 H II regions (emission nebulae) intended to be comprehensive north of declination −27°. (It does include some nebulae south of that declination as well.) The first edition was published in 1953 with 142 objects (Sh1), and the second and final version was published by US astronomer Stewart Sharpless in 1959 with 312 objects.

Key takeaways

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

Reference excerpt

The Sharpless catalog is a list of 313 H II regions (emission nebulae) intended to be comprehensive north of declination −27°. (It does include some nebulae south of that declination as well.) The first edition was published in 1953 with 142 objects (Sh1), and the second and final version was published by US astronomer Stewart Sharpless in 1959 with 312 objects. Sharpless also includes some planetary nebulae and supernova remnants, in addition to H II regions. In 1953 Stewart Sharpless joined the staff of the United States Naval Observatory Flagstaff Station, where he surveyed and cataloged H II regions of the Milky Way using the images from the Palomar Sky Survey. From this work Sharpless published his catalog of H II regions in two editions: the first in 1953, with 142 nebulae; and the second and final edition in 1959, with 312 nebulae. Sharpless coordinates are based on the star catalogs Bonner Durchmusterung (BD) and Cordoba Durchmusterung (CD), but the second release was adjusted to the 1900 epoch. In the second release, some coordinates for southern hemisphere regions have an uncertainty over 1 minute of arc. This can make them difficult to find, so a revised catalog called BFS (Blitz, Fich and Stark) was released with 65 new regions and about 20 removals. Most of the removed items were the aforementioned nebula or remnants. The 312 items in Sharpless sometimes overlap with the 110 Messier objects (M), 7,840 objects in the New General Catalogue (NGC), the Caldwell catalogue (itself a "best of" from other catalogues, with 109 items), and the RCW catalog. Contemporary catalogs were Gum and RCW, but they mainly covered the southern hemisphere.

Table Table of second Sharpless (1958 version) catalog; click on image for image credit, most of which are either various amateur astronomers, the ESO, ESA, or NASA

List

See also Gum Catalog RCW Catalog List of star-forming regions in the Local Group

References

External links Original catalog Illustrated and annotated commentary SIMBAD Sh2 listing Sh2 images

Illustrations

Worked examples

Example 1 — a first encounter with Sharpless catalog

Start with the simplest possible case. Write down what Sharpless catalog 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 Sharpless catalog 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 Sharpless catalog 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 Sharpless catalog

In research: Sharpless catalog 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 Sharpless catalog 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: Sharpless catalog is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1953 documents, 1953 in science, Astronomical catalogues of nebulae, so understanding it makes those chapters shorter.
In everyday life: Look for Sharpless catalog 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 Sharpless catalog in 20 minutes

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

Frequently asked questions

What is Sharpless catalog in simple terms?

Why does Sharpless catalog 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 Sharpless catalog?

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 Sharpless catalog.