What are the uses of spherical harmonics?

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SUMMARY

Spherical harmonics are functions defined on a sphere, specifically dependent on the angles θ and φ, and do not include the radial component r. They serve as eigenfunctions of the angular part of the Laplace operator, enabling the separation of angular and radial components in problems. Additionally, spherical harmonics are utilized for series expansion of functions defined on the surface of a sphere, such as analyzing cosmic microwave background (CMB) temperature variations.

PREREQUISITES
  • Understanding of spherical coordinates
  • Familiarity with the Laplace equation
  • Knowledge of eigenfunctions and operators
  • Basic concepts of series expansion in mathematical analysis
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  • Study the properties of spherical harmonics in mathematical physics
  • Learn about the separation of variables technique in solving partial differential equations
  • Explore applications of spherical harmonics in cosmology, particularly in CMB analysis
  • Investigate the relationship between spherical harmonics and Fourier series
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Mathematicians, physicists, and engineers interested in solving problems involving spherical coordinates, as well as researchers analyzing cosmic microwave background data.

member 428835
Hi PF!

When solving the Laplace equation in spherical coordinates, the spherical harmonics are functions of ##\phi,\theta## but not ##r##. Why don't they include the ##r## component?

Thanks!
 
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joshmccraney said:
Hi PF!

When solving the Laplace equation in spherical coordinates, the spherical harmonics are functions of ##\phi,\theta## but not ##r##. Why don't they include the ##r## component?

Thanks!
Because they are functions of ##\theta## and ##\phi## by definition. They are functions defined on a sphere and are the eigenfunctions of the angular part of the Laplace operator.

Of course, if you want to make an expansion of a function of ##r##, ##\theta##, and ##\phi## in terms of spherical harmonics, then the expansion coefficients will depend on ##r##. This is just separation of variabels and should be well described in any textbook on the subject.
 
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joshmccraney said:
Why don't they include the rr component?
Orodruin said:
Because they are functions of θ\theta and ϕ\phi by definition.

Right. They are useful because they allow you to separate out the angular and radial parts of the problem.
 
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Vanadium 50 said:
Right. They are useful because they allow you to separate out the angular and radial parts of the problem.
In this particular instance, yes. Generally they have other uses as well - such as series expanding any function defined on the surface of a sphere (eg, the CMB temperature variations).
 
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