astronomy

Local Sheet

Local Sheet 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 Local Sheet rather than just read about it. In short: The Local Sheet or the Coma–Sculptor Cloud is a nearby galaxy filament and an extragalactic region of space where the Milky Way, the members of the Local Group, and other galaxies share a similar peculiar velocity. This region lies within a diameter of about 10.4 megaparsecs (34 million light-years; 3.2×1020 kilometres), 465 kiloparsecs (1.52 million light-years; 1.43×1019 kilometres) thick, and galaxies beyond that…

Key takeaways

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

Reference excerpt

The Local Sheet or the Coma–Sculptor Cloud is a nearby galaxy filament and an extragalactic region of space where the Milky Way, the members of the Local Group, and other galaxies share a similar peculiar velocity. This region lies within a diameter of about 10.4 megaparsecs (34 million light-years; 3.2×1020 kilometres), 465 kiloparsecs (1.52 million light-years; 1.43×1019 kilometres) thick, and galaxies beyond that distance show markedly different velocities. The Local Group has only a relatively small peculiar velocity of 66 km⋅s−1 with respect to the Local Sheet. Typical velocity dispersion of galaxies is only 40 km⋅s−1 in the radial direction. Nearly all nearby bright galaxies belong to the Local Sheet. The Local Sheet is part of the Local Volume and is in the Virgo Supercluster (Local Supercluster). The Local Sheet forms a wall of galaxies delineating one boundary of the Local Void. A significant component of the mean velocity of the galaxies in the Local Sheet appears as the result of the gravitational attraction of the Virgo Cluster of galaxies, resulting in a peculiar motion ~185 km⋅s−1 toward the cluster. A second component is directed away from the center of the Local Void; an expanding region of space spanning an estimated 45 Mpc (150 Mly) that is only sparsely populated with galaxies. This component has a velocity of 259 km⋅s−1. The Local Sheet is inclined 8° from the Local Supercluster (Virgo Supercluster). The so-called Council of Giants is a ring of twelve large galaxies surrounding the Local Group in the Local Sheet, with a radius of 3.746 Mpc (12.22 Mly) and its center located at 810 kpc (2.6 Mly) away from the Sun. Ten of these are spirals, while the remaining two are ellipticals. The two ellipticals (Maffei 1 and Centaurus A) lie on opposite sides of the Local Group.

* The mass is given as the logarithm (base unspecified) of the mass in solar masses.

Location The Local Sheet is the co-moving part of the Coma-Sculptor Cloud, which was identified and described in 1987 by astronomer Brent Tully with colleague Richard Fisher in his book The Nearby Galaxies Atlas as Cloud 14. It is a huge 10 Mpc (33 Mly) prolate, filament and is mostly host to late-type galaxies, in contrast to the Virgo Cluster, in which more than half of the giant galaxies are early-type galaxies. Tully maintains that the Coma-Sculptor Cloud and the Local Sheet do not quite overlap, as the Local Sheet comprises only the co-moving part of the Coma-Sculptor Cloud. McCall considers the two terms synonymous, referring to one and the same region.

See also Supergalactic coordinate system, the coordinate system taking the Local Sheet, the Supergalactic Plane, as its X–Y bases

References

Illustrations

Worked examples

Example 1 — a first encounter with Local Sheet

Start with the simplest possible case. Write down what Local Sheet 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 Local Sheet 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 Local Sheet 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 Local Sheet

In research: Local Sheet 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 Local Sheet 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: Local Sheet is common in secondary-school and first-year university syllabi. It links to neighbouring topics Galaxy superclusters, Large-scale structure of the cosmos, Local Sheet, so understanding it makes those chapters shorter.
In everyday life: Look for Local Sheet 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 Local Sheet in 20 minutes

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

Frequently asked questions

What is Local Sheet in simple terms?

Why does Local Sheet 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 Local Sheet?

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 Local Sheet.